Removing characters from string efficiently

Removing characters from string efficiently - java

This may sound like a very simple question but how do you remove multiple different characters from a string without having to write a line for each, which is what I have laboriously done. I have written a string example below:
String word = "Hello, t-his is; an- (example) line."
word = word.replace(",", "");
word = word.replace(".", "");
word = word.replace(";", "");
word = word.replace("-", "");
word = word.replace("(", "");
word = word.replace(")", "");
System.out.println(word);
Which would produce "Hello this is an example line". A more efficient way is?

Use
word = word.replaceAll("[,.;\\-()]", "");
Note that special character - (hyphen) should be escaped by double backslashes, because otherwise it is considered to construct a range.

Although no more efficient than the original replace technique you could use
word = word.replaceAll("\\p{Punct}+", "");
to use a simple expression using replaceAll with a wider range of characters replaced

Without (ab)using regex, I would do that way:
String word = "Hello, t-his is; an- (example) line.";
String undesirable = ",.;-()";
int len1 = undesirable.length();
int len2 = word.length();
StringBuilder sb = new StringBuilder(len2);
outer: for (int j = 0; j < len2; j++) {
char c = word.charAt(j);
for (int i = 0; i < len; i++) {
if (c == undesirable.charAt(i)) continue outer;
}
sb.append(c);
}
System.out.println(sb.toString());
The advantage is performance. You don't need the overhead of creating and parsing a regular expression.
You could encapsulate that in a method:
public static String removeCharacters(String word, String undesirable) {
int len1 = undesirable.length();
int len2 = word.length();
StringBuilder sb = new StringBuilder(len2);
outer: for (int j = 0; j < len2; j++) {
char c = word.charAt(j);
for (int i = 0; i < len1; i++) {
if (c == undesirable.charAt(i)) continue outer;
}
sb.append(c);
}
return sb.toString();
}
public static String removeSpecialCharacters(String word) {
return removeCharacters(word, ",.;-()");
}
And then, you would use it this way:
public static void testMethod() {
String word = "Hello, t-his is; an- (example) line.";
System.out.println(removeSpecialCharacters(word));
}
Here is a performance test:
public class WordTest {
public static void main(String[] args) {
int iterations = 10000000;
long t1 = System.currentTimeMillis();
for (int i = 0; i < iterations; i++) {
testAsArray();
}
long t2 = System.currentTimeMillis();
for (int i = 0; i < iterations; i++) {
testRegex();
}
long t3 = System.currentTimeMillis();
for (int i = 0; i < iterations; i++) {
testAsString();
}
long t4 = System.currentTimeMillis();
System.out.println("Without regex, but using copied arrays: " + (t2 - t1));
System.out.println("With precompiled regex: " + (t3 - t2));
System.out.println("Without regex, but using string: " + (t4 - t3));
}
public static void testAsArray() {
String word = "Hello, t-his is; an- (example) line.";
char[] undesirable = ",.;-()".toCharArray();
StringBuilder sb = new StringBuilder(word.length());
outer: for (char c : word.toCharArray()) {
for (char h : undesirable) {
if (c == h) continue outer;
}
sb.append(c);
}
sb.toString();
}
public static void testAsString() {
String word = "Hello, t-his is; an- (example) line.";
String undesirable = ",.;-()";
int len1 = undesirable.length();
int len2 = word.length();
StringBuilder sb = new StringBuilder(len2);
outer: for (int j = 0; j < len2; j++) {
char c = word.charAt(j);
for (int i = 0; i < len1; i++) {
if (c == undesirable.charAt(i)) continue outer;
}
sb.append(c);
}
sb.toString();
}
private static final Pattern regex = Pattern.compile("[,\\.;\\-\\(\\)]");
public static void testRegex() {
String word = "Hello, t-his is; an- (example) line.";
String result = regex.matcher(word).replaceAll("");
}
}
The output on my machine:
Without regex, but using copied arrays: 5880
With precompiled regex: 11011
Without regex, but using string: 3844

Here is a solution to do this with minimal effort; the toRemove string contains all character you don't want to see in the output:
public static String removeChars(final String input, final String toRemove)
{
final StringBuilder sb = new StringBuilder(input.length());
final CharBuffer buf = CharBuffer.wrap(input);
char c;
while (buf.hasRemaining()) {
c = buf.get();
if (toRemove.indexOf(c) == -1)
sb.append(c);
}
return sb.toString();
}
If you use Java 8 you can even use this (unfortunately there's no CharStream so the casts are necessary...):
public static String removeChars(final String input, final String toRemove)
{
final StringBuilder sb = new StringBuilder(input.length());
input.chars().filter(c -> toRemove.indexOf((char) c) == -1)
.forEach(i -> sb.append((char) i));
return sb.toString();
}

You could try using a regular expression with Java's String.replaceAll method:
word = word.replaceAll(",|\.|;|-|\(|\)", "");
If you're not familiar with regular expressions, | means "or". So we are essentially saying , or . or ; or - or ( or ).
See more: Java documentation for String.replaceAll
Edit:
As mentioned, my previous version will not compile. Just for the sake of correctness (even though it has been pointed out that this is not the optimal solution), here is the corrected version of my regex:
word = word.replaceAll(",|\\.|;|-|\\(|\\)", "");

Related

Rewriting the String in Reverse [duplicate]

I have "Hello World" kept in a String variable named hi.
I need to print it, but reversed.
How can I do this? I understand there is some kind of a function already built-in into Java that does that.
Related: Reverse each individual word of “Hello World” string with Java

You can use this:
new StringBuilder(hi).reverse().toString()
StringBuilder was added in Java 5. For versions prior to Java 5, the StringBuffer class can be used instead — it has the same API.

For Online Judges problems that does not allow StringBuilder or StringBuffer, you can do it in place using char[] as following:
public static String reverse(String input){
char[] in = input.toCharArray();
int begin=0;
int end=in.length-1;
char temp;
while(end>begin){
temp = in[begin];
in[begin]=in[end];
in[end] = temp;
end--;
begin++;
}
return new String(in);
}

public static String reverseIt(String source) {
int i, len = source.length();
StringBuilder dest = new StringBuilder(len);
for (i = (len - 1); i >= 0; i--){
dest.append(source.charAt(i));
}
return dest.toString();
}
http://www.java2s.com/Code/Java/Language-Basics/ReverseStringTest.htm

String string="whatever";
String reverse = new StringBuffer(string).reverse().toString();
System.out.println(reverse);

I am doing this by using the following two ways:
Reverse string by CHARACTERS:
public static void main(String[] args) {
// Using traditional approach
String result="";
for(int i=string.length()-1; i>=0; i--) {
result = result + string.charAt(i);
}
System.out.println(result);
// Using StringBuffer class
StringBuffer buffer = new StringBuffer(string);
System.out.println(buffer.reverse());
}
Reverse string by WORDS:
public static void reverseStringByWords(String string) {
StringBuilder stringBuilder = new StringBuilder();
String[] words = string.split(" ");
for (int j = words.length-1; j >= 0; j--) {
stringBuilder.append(words[j]).append(' ');
}
System.out.println("Reverse words: " + stringBuilder);
}

Take a look at the Java 6 API under StringBuffer
String s = "sample";
String result = new StringBuffer(s).reverse().toString();

Here is an example using recursion:
public void reverseString() {
String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
String reverseAlphabet = reverse(alphabet, alphabet.length()-1);
}
String reverse(String stringToReverse, int index){
if(index == 0){
return stringToReverse.charAt(0) + "";
}
char letter = stringToReverse.charAt(index);
return letter + reverse(stringToReverse, index-1);
}

Here is a low level solution:
import java.util.Scanner;
public class class1 {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
String inpStr = in.nextLine();
System.out.println("Original String :" + inpStr);
char temp;
char[] arr = inpStr.toCharArray();
int len = arr.length;
for(int i=0; i<(inpStr.length())/2; i++,len--){
temp = arr[i];
arr[i] = arr[len-1];
arr[len-1] = temp;
}
System.out.println("Reverse String :" + String.valueOf(arr));
}
}

I tried, just for fun, by using a Stack. Here my code:
public String reverseString(String s) {
Stack<Character> stack = new Stack<>();
StringBuilder sb = new StringBuilder();
for (int i = 0; i < s.length(); i++) {
stack.push(s.charAt(i));
}
while (!stack.empty()) {
sb.append(stack.pop());
}
return sb.toString();
}

Since the below method (using XOR) to reverse a string is not listed, I am attaching this method to reverse a string.
The Algorithm is based on :
1.(A XOR B) XOR B = A
2.(A XOR B) XOR A = B
Code snippet:
public class ReverseUsingXOR {
public static void main(String[] args) {
String str = "prateek";
reverseUsingXOR(str.toCharArray());
}
/*Example:
* str= prateek;
* str[low]=p;
* str[high]=k;
* str[low]=p^k;
* str[high]=(p^k)^k =p;
* str[low]=(p^k)^p=k;
*
* */
public static void reverseUsingXOR(char[] str) {
int low = 0;
int high = str.length - 1;
while (low < high) {
str[low] = (char) (str[low] ^ str[high]);
str[high] = (char) (str[low] ^ str[high]);
str[low] = (char) (str[low] ^ str[high]);
low++;
high--;
}
//display reversed string
for (int i = 0; i < str.length; i++) {
System.out.print(str[i]);
}
}
}
Output:
keetarp

As others have pointed out the preferred way is to use:
new StringBuilder(hi).reverse().toString()
But if you want to implement this by yourself, I'm afraid that the rest of responses have flaws.
The reason is that String represents a list of Unicode points, encoded in a char[] array according to the variable-length encoding: UTF-16.
This means some code points use a single element of the array (one code unit) but others use two of them, so there might be pairs of characters that must be treated as a single unit (consecutive "high" and "low" surrogates).
public static String reverseString(String s) {
char[] chars = new char[s.length()];
boolean twoCharCodepoint = false;
for (int i = 0; i < s.length(); i++) {
chars[s.length() - 1 - i] = s.charAt(i);
if (twoCharCodepoint) {
swap(chars, s.length() - 1 - i, s.length() - i);
}
twoCharCodepoint = !Character.isBmpCodePoint(s.codePointAt(i));
}
return new String(chars);
}
private static void swap(char[] array, int i, int j) {
char temp = array[i];
array[i] = array[j];
array[j] = temp;
}
public static void main(String[] args) throws Exception {
FileOutputStream fos = new FileOutputStream("C:/temp/reverse-string.txt");
StringBuilder sb = new StringBuilder("Linear B Syllable B008 A: ");
sb.appendCodePoint(65536); //http://unicode-table.com/es/#10000
sb.append(".");
fos.write(sb.toString().getBytes("UTF-16"));
fos.write("\n".getBytes("UTF-16"));
fos.write(reverseString(sb.toString()).getBytes("UTF-16"));
}

Using charAt() method
String name = "gaurav";
String reversedString = "";
for(int i = name.length()-1; i>=0; i--){
reversedString = reversedString + name.charAt(i);
}
System.out.println(reversedString);
Using toCharArray() method
String name = "gaurav";
char [] stringCharArray = name.toCharArray();
String reversedString = "";
for(int i = stringCharArray.length-1; i>=0; i--) {
reversedString = reversedString + stringCharArray[i];
}
System.out.println(reversedString);
Using reverse() method of the Stringbuilder
String name = "gaurav";
String reversedString = new StringBuilder(name).reverse().toString();
System.out.println(reversedString);
Check https://coderolls.com/reverse-a-string-in-java/

It is very simple in minimum code of lines
public class ReverseString {
public static void main(String[] args) {
String s1 = "neelendra";
for(int i=s1.length()-1;i>=0;i--)
{
System.out.print(s1.charAt(i));
}
}
}

This did the trick for me
public static void main(String[] args) {
String text = "abcdefghijklmnopqrstuvwxyz";
for (int i = (text.length() - 1); i >= 0; i--) {
System.out.print(text.charAt(i));
}
}

1. Using Character Array:
public String reverseString(String inputString) {
char[] inputStringArray = inputString.toCharArray();
String reverseString = "";
for (int i = inputStringArray.length - 1; i >= 0; i--) {
reverseString += inputStringArray[i];
}
return reverseString;
}
2. Using StringBuilder:
public String reverseString(String inputString) {
StringBuilder stringBuilder = new StringBuilder(inputString);
stringBuilder = stringBuilder.reverse();
return stringBuilder.toString();
}
OR
return new StringBuilder(inputString).reverse().toString();

System.out.print("Please enter your name: ");
String name = keyboard.nextLine();
String reverse = new StringBuffer(name).reverse().toString();
String rev = reverse.toLowerCase();
System.out.println(rev);
I used this method to turn names backwards and into lower case.

One natural way to reverse a String is to use a StringTokenizer and a stack. Stack is a class that implements an easy-to-use last-in, first-out (LIFO) stack of objects.
String s = "Hello My name is Sufiyan";
Put it in the stack frontwards
Stack<String> myStack = new Stack<>();
StringTokenizer st = new StringTokenizer(s);
while (st.hasMoreTokens()) {
myStack.push(st.nextToken());
}
Print the stack backwards
System.out.print('"' + s + '"' + " backwards by word is:\n\t\"");
while (!myStack.empty()) {
System.out.print(myStack.pop());
System.out.print(' ');
}
System.out.println('"');

public String reverse(String s) {
String reversedString = "";
for(int i=s.length(); i>0; i--) {
reversedString += s.charAt(i-1);
}
return reversedString;
}

public class Test {
public static void main(String args[]) {
StringBuffer buffer = new StringBuffer("Game Plan");
buffer.reverse();
System.out.println(buffer);
}
}

All above solution is too good but here I am making reverse string using recursive programming.
This is helpful for who is looking recursive way of doing reverse string.
public class ReversString {
public static void main(String args[]) {
char s[] = "Dhiral Pandya".toCharArray();
String r = new String(reverse(0, s));
System.out.println(r);
}
public static char[] reverse(int i, char source[]) {
if (source.length / 2 == i) {
return source;
}
char t = source[i];
source[i] = source[source.length - 1 - i];
source[source.length - 1 - i] = t;
i++;
return reverse(i, source);
}
}

You can also try this:
public class StringReverse {
public static void main(String[] args) {
String str = "Dogs hates cats";
StringBuffer sb = new StringBuffer(str);
System.out.println(sb.reverse());
}
}

Procedure :
We can use split() to split the string .Then use reverse loop and add the characters.
Code snippet:
class test
{
public static void main(String args[])
{
String str = "world";
String[] split= str.split("");
String revers = "";
for (int i = split.length-1; i>=0; i--)
{
revers += split[i];
}
System.out.printf("%s", revers);
}
}
//output : dlrow

It gets the value you typed and returns it reversed ;)
public static String reverse (String a){
char[] rarray = a.toCharArray();
String finalvalue = "";
for (int i = 0; i < rarray.length; i++)
{
finalvalue += rarray[rarray.length - 1 - i];
}
return finalvalue;
}

public String reverseWords(String s) {
String reversedWords = "";
if(s.length()<=0) {
return reversedWords;
}else if(s.length() == 1){
if(s == " "){
return "";
}
return s;
}
char arr[] = s.toCharArray();
int j = arr.length-1;
while(j >= 0 ){
if( arr[j] == ' '){
reversedWords+=arr[j];
}else{
String temp="";
while(j>=0 && arr[j] != ' '){
temp+=arr[j];
j--;
}
j++;
temp = reverseWord(temp);
reversedWords+=temp;
}
j--;
}
String[] chk = reversedWords.split(" ");
if(chk == null || chk.length == 0){
return "";
}
return reversedWords;
}
public String reverseWord(String s){
char[] arr = s.toCharArray();
for(int i=0,j=arr.length-1;i<=j;i++,j--){
char tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
return String.valueOf(arr);
}

public static void main(String[] args) {
String str = "Prashant";
int len = str.length();
char[] c = new char[len];
for (int j = len - 1, i = 0; j >= 0; j--, i++) {
c[i] = str.charAt(j);
}
str = String.copyValueOf(c);
System.out.println(str);
}

public void reverString(){
System.out.println("Enter value");
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
try{
String str=br.readLine();
char[] charArray=str.toCharArray();
for(int i=charArray.length-1; i>=0; i--){
System.out.println(charArray[i]);
}
}
catch(IOException ex){
}

recursion:
public String stringReverse(String string) {
if (string == null || string.length() == 0) {
return string;
}
return stringReverse(string.substring(1)) + string.charAt(0);
}

Sequence of characters (or) StringString's Family:
String testString = "Yashwanth#777"; // ~1 1⁄4→D800₁₆«2²⁰
Using Java 8 Stream API
First we convert String into stream by using method CharSequence.chars(), then we use the method IntStream.range to generate a sequential stream of numbers. Then we map this sequence of stream into String.
public static String reverseString_Stream(String str) {
IntStream cahrStream = str.chars();
final int[] array = cahrStream.map( x -> x ).toArray();
int from = 0, upTo = array.length;
IntFunction<String> reverseMapper = (i) -> ( Character.toString((char) array[ (upTo - i) + (from - 1) ]) );
String reverseString = IntStream.range(from, upTo) // for (int i = from; i < upTo ; i++) { ... }
.mapToObj( reverseMapper ) // array[ lastElement ]
.collect(Collectors.joining()) // Joining stream of elements together into a String.
.toString(); // This object (which is already a string!) is itself returned.
System.out.println("Reverse Stream as String : "+ reverseString);
return reverseString;
}
Using a Traditional for Loop
If you want to reverse the string then we need to follow these steps.
Convert String into an Array of Characters.
Iterate over an array in reverse order, append each Character to temporary string variable until the last character.
public static String reverseString( String reverse ) {
if( reverse != null && reverse != "" && reverse.length() > 0 ) {
char[] arr = reverse.toCharArray();
String temp = "";
for( int i = arr.length-1; i >= 0; i-- ) {
temp += arr[i];
}
System.out.println("Reverse String : "+ temp);
}
return null;
}
Easy way to Use reverse method provided form StringBuffer or StringBuilder Classes
StringBuilder and StringBuffer are mutable sequence of characters. That means one can change the value of these object's.
StringBuffer buffer = new StringBuffer(str);
System.out.println("StringBuffer - reverse : "+ buffer.reverse() );
String builderString = (new StringBuilder(str)).reverse().toString;
System.out.println("StringBuilder generated reverse String : "+ builderString );
StringBuffer has the same methods as the StringBuilder, but each method in StringBuffer is synchronized so it is thread safe.

public static String revString(String str){
char[] revCharArr = str.toCharArray();
for (int i=0; i< str.length()/2; i++){
char f = revCharArr[i];
char l = revCharArr[str.length()-i-1];
revCharArr[i] = l;
revCharArr[str.length()-i-1] = f;
}
String revStr = new String(revCharArr);
return revStr;
}

Simple For loop in java
public void reverseString(char[] s) {
int length = s.length;
for (int i = 0; i < s.length / 2; i++) {
// swaping character
char temp = s[length - i - 1];
s[length - i - 1] = s[i];
s[i] = temp;
}
}

Replacing the number with the number of spaces

I have a String:
String example = "AA5DD2EE3MM";
I want to replace the number with the number of spaces. Example:
String example = "AA DD EE MM"
If the String would be
String anotherExample = "a3ee"
It should turn into:
String anotherExample = "a ee"
I want to do it for any string. Not only for the examples above.

Split your input at digit and non digit chars as a stream, map digits to the corsponding number of spaces using String.repeat, collect to string using Collectors.joining():
String input = "AA5DD2EE3MM";
String regex = "(?<=\\D)(?=\\d)|(?<=\\d)(?=\\D)";
String result = Pattern.compile(regex)
.splitAsStream(input)
.map(s -> s.matches("\\d+") ? " ".repeat(Integer.parseInt(s)) : s)
.collect(Collectors.joining());

You could also use this approach, which is simpler but also far less elegant:
String example = "a4aa";
String newString = "";
for (int i = 0; i < example.length(); i++) {
if (Character.isDigit(example.charAt(i))) {
for (int a = 0; a < Character.getNumericValue(example.charAt(i)); a++) {
newString += " ";
}
} else {
newString += example.charAt(i);
}
}
System.out.println(newString);

Using a pattern matcher approach:
String input = "AA5DD2EE3MM";
Pattern pattern = Pattern.compile("\\d+");
Matcher m = pattern.matcher(input);
StringBuffer buffer = new StringBuffer();
while (m.find()) {
m.appendReplacement(buffer,new String(new char[Integer.valueOf(m.group())]).replace("\0", " "));
}
m.appendTail(buffer);
System.out.println(buffer.toString()); // AA DD EE MM
The idea here is to iterate the string, pausing at each digit match. We replace each digit with space replicated the same number of times as the digit.

public static String replaceDigitsWithSpaces(String input) {
String result = "";
int len = input.length(), i =0;
while( i < len) {
if(Character.isLetter(input.charAt(i))) {
result += input.charAt(i);
}else if(Character.isDigit(input.charAt(i))) {
//generate number upto characters
int k = 0, j = i;
String temp = "";
while(j < len) {
if(Character.isDigit(input.charAt(j))) {
temp += input.charAt(j);
j++;
}else {
break;
}
}
k = Integer.parseInt(temp);
while(k != 0) {
result+= " ";
k--;
}
i = j;
continue;
}
i++;
}
return result;
}
input:: "AA23BB1C11C8"<br>
output:: AA BB C C .

StringBuilder is more efficient for concatenation:
public static String spaceIt(String s) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (Character.isDigit(c)) {
for (int j = 0; j < Character.digit(c, 10); j++) {
sb.append(' ');
}
} else {
sb.append(c);
}
}
return sb.toString();
}

Is reversing a string this way bad practice? [Java] [duplicate]

I have "Hello World" kept in a String variable named hi.
I need to print it, but reversed.
How can I do this? I understand there is some kind of a function already built-in into Java that does that.
Related: Reverse each individual word of “Hello World” string with Java

You can use this:
new StringBuilder(hi).reverse().toString()
StringBuilder was added in Java 5. For versions prior to Java 5, the StringBuffer class can be used instead — it has the same API.

For Online Judges problems that does not allow StringBuilder or StringBuffer, you can do it in place using char[] as following:
public static String reverse(String input){
char[] in = input.toCharArray();
int begin=0;
int end=in.length-1;
char temp;
while(end>begin){
temp = in[begin];
in[begin]=in[end];
in[end] = temp;
end--;
begin++;
}
return new String(in);
}

public static String reverseIt(String source) {
int i, len = source.length();
StringBuilder dest = new StringBuilder(len);
for (i = (len - 1); i >= 0; i--){
dest.append(source.charAt(i));
}
return dest.toString();
}
http://www.java2s.com/Code/Java/Language-Basics/ReverseStringTest.htm

String string="whatever";
String reverse = new StringBuffer(string).reverse().toString();
System.out.println(reverse);

I am doing this by using the following two ways:
Reverse string by CHARACTERS:
public static void main(String[] args) {
// Using traditional approach
String result="";
for(int i=string.length()-1; i>=0; i--) {
result = result + string.charAt(i);
}
System.out.println(result);
// Using StringBuffer class
StringBuffer buffer = new StringBuffer(string);
System.out.println(buffer.reverse());
}
Reverse string by WORDS:
public static void reverseStringByWords(String string) {
StringBuilder stringBuilder = new StringBuilder();
String[] words = string.split(" ");
for (int j = words.length-1; j >= 0; j--) {
stringBuilder.append(words[j]).append(' ');
}
System.out.println("Reverse words: " + stringBuilder);
}

Take a look at the Java 6 API under StringBuffer
String s = "sample";
String result = new StringBuffer(s).reverse().toString();

Here is an example using recursion:
public void reverseString() {
String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
String reverseAlphabet = reverse(alphabet, alphabet.length()-1);
}
String reverse(String stringToReverse, int index){
if(index == 0){
return stringToReverse.charAt(0) + "";
}
char letter = stringToReverse.charAt(index);
return letter + reverse(stringToReverse, index-1);
}

Here is a low level solution:
import java.util.Scanner;
public class class1 {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
String inpStr = in.nextLine();
System.out.println("Original String :" + inpStr);
char temp;
char[] arr = inpStr.toCharArray();
int len = arr.length;
for(int i=0; i<(inpStr.length())/2; i++,len--){
temp = arr[i];
arr[i] = arr[len-1];
arr[len-1] = temp;
}
System.out.println("Reverse String :" + String.valueOf(arr));
}
}

I tried, just for fun, by using a Stack. Here my code:
public String reverseString(String s) {
Stack<Character> stack = new Stack<>();
StringBuilder sb = new StringBuilder();
for (int i = 0; i < s.length(); i++) {
stack.push(s.charAt(i));
}
while (!stack.empty()) {
sb.append(stack.pop());
}
return sb.toString();
}

Since the below method (using XOR) to reverse a string is not listed, I am attaching this method to reverse a string.
The Algorithm is based on :
1.(A XOR B) XOR B = A
2.(A XOR B) XOR A = B
Code snippet:
public class ReverseUsingXOR {
public static void main(String[] args) {
String str = "prateek";
reverseUsingXOR(str.toCharArray());
}
/*Example:
* str= prateek;
* str[low]=p;
* str[high]=k;
* str[low]=p^k;
* str[high]=(p^k)^k =p;
* str[low]=(p^k)^p=k;
*
* */
public static void reverseUsingXOR(char[] str) {
int low = 0;
int high = str.length - 1;
while (low < high) {
str[low] = (char) (str[low] ^ str[high]);
str[high] = (char) (str[low] ^ str[high]);
str[low] = (char) (str[low] ^ str[high]);
low++;
high--;
}
//display reversed string
for (int i = 0; i < str.length; i++) {
System.out.print(str[i]);
}
}
}
Output:
keetarp

As others have pointed out the preferred way is to use:
new StringBuilder(hi).reverse().toString()
But if you want to implement this by yourself, I'm afraid that the rest of responses have flaws.
The reason is that String represents a list of Unicode points, encoded in a char[] array according to the variable-length encoding: UTF-16.
This means some code points use a single element of the array (one code unit) but others use two of them, so there might be pairs of characters that must be treated as a single unit (consecutive "high" and "low" surrogates).
public static String reverseString(String s) {
char[] chars = new char[s.length()];
boolean twoCharCodepoint = false;
for (int i = 0; i < s.length(); i++) {
chars[s.length() - 1 - i] = s.charAt(i);
if (twoCharCodepoint) {
swap(chars, s.length() - 1 - i, s.length() - i);
}
twoCharCodepoint = !Character.isBmpCodePoint(s.codePointAt(i));
}
return new String(chars);
}
private static void swap(char[] array, int i, int j) {
char temp = array[i];
array[i] = array[j];
array[j] = temp;
}
public static void main(String[] args) throws Exception {
FileOutputStream fos = new FileOutputStream("C:/temp/reverse-string.txt");
StringBuilder sb = new StringBuilder("Linear B Syllable B008 A: ");
sb.appendCodePoint(65536); //http://unicode-table.com/es/#10000
sb.append(".");
fos.write(sb.toString().getBytes("UTF-16"));
fos.write("\n".getBytes("UTF-16"));
fos.write(reverseString(sb.toString()).getBytes("UTF-16"));
}

Using charAt() method
String name = "gaurav";
String reversedString = "";
for(int i = name.length()-1; i>=0; i--){
reversedString = reversedString + name.charAt(i);
}
System.out.println(reversedString);
Using toCharArray() method
String name = "gaurav";
char [] stringCharArray = name.toCharArray();
String reversedString = "";
for(int i = stringCharArray.length-1; i>=0; i--) {
reversedString = reversedString + stringCharArray[i];
}
System.out.println(reversedString);
Using reverse() method of the Stringbuilder
String name = "gaurav";
String reversedString = new StringBuilder(name).reverse().toString();
System.out.println(reversedString);
Check https://coderolls.com/reverse-a-string-in-java/

It is very simple in minimum code of lines
public class ReverseString {
public static void main(String[] args) {
String s1 = "neelendra";
for(int i=s1.length()-1;i>=0;i--)
{
System.out.print(s1.charAt(i));
}
}
}

This did the trick for me
public static void main(String[] args) {
String text = "abcdefghijklmnopqrstuvwxyz";
for (int i = (text.length() - 1); i >= 0; i--) {
System.out.print(text.charAt(i));
}
}

1. Using Character Array:
public String reverseString(String inputString) {
char[] inputStringArray = inputString.toCharArray();
String reverseString = "";
for (int i = inputStringArray.length - 1; i >= 0; i--) {
reverseString += inputStringArray[i];
}
return reverseString;
}
2. Using StringBuilder:
public String reverseString(String inputString) {
StringBuilder stringBuilder = new StringBuilder(inputString);
stringBuilder = stringBuilder.reverse();
return stringBuilder.toString();
}
OR
return new StringBuilder(inputString).reverse().toString();

System.out.print("Please enter your name: ");
String name = keyboard.nextLine();
String reverse = new StringBuffer(name).reverse().toString();
String rev = reverse.toLowerCase();
System.out.println(rev);
I used this method to turn names backwards and into lower case.

One natural way to reverse a String is to use a StringTokenizer and a stack. Stack is a class that implements an easy-to-use last-in, first-out (LIFO) stack of objects.
String s = "Hello My name is Sufiyan";
Put it in the stack frontwards
Stack<String> myStack = new Stack<>();
StringTokenizer st = new StringTokenizer(s);
while (st.hasMoreTokens()) {
myStack.push(st.nextToken());
}
Print the stack backwards
System.out.print('"' + s + '"' + " backwards by word is:\n\t\"");
while (!myStack.empty()) {
System.out.print(myStack.pop());
System.out.print(' ');
}
System.out.println('"');

public String reverse(String s) {
String reversedString = "";
for(int i=s.length(); i>0; i--) {
reversedString += s.charAt(i-1);
}
return reversedString;
}

public class Test {
public static void main(String args[]) {
StringBuffer buffer = new StringBuffer("Game Plan");
buffer.reverse();
System.out.println(buffer);
}
}

All above solution is too good but here I am making reverse string using recursive programming.
This is helpful for who is looking recursive way of doing reverse string.
public class ReversString {
public static void main(String args[]) {
char s[] = "Dhiral Pandya".toCharArray();
String r = new String(reverse(0, s));
System.out.println(r);
}
public static char[] reverse(int i, char source[]) {
if (source.length / 2 == i) {
return source;
}
char t = source[i];
source[i] = source[source.length - 1 - i];
source[source.length - 1 - i] = t;
i++;
return reverse(i, source);
}
}

You can also try this:
public class StringReverse {
public static void main(String[] args) {
String str = "Dogs hates cats";
StringBuffer sb = new StringBuffer(str);
System.out.println(sb.reverse());
}
}

Procedure :
We can use split() to split the string .Then use reverse loop and add the characters.
Code snippet:
class test
{
public static void main(String args[])
{
String str = "world";
String[] split= str.split("");
String revers = "";
for (int i = split.length-1; i>=0; i--)
{
revers += split[i];
}
System.out.printf("%s", revers);
}
}
//output : dlrow

It gets the value you typed and returns it reversed ;)
public static String reverse (String a){
char[] rarray = a.toCharArray();
String finalvalue = "";
for (int i = 0; i < rarray.length; i++)
{
finalvalue += rarray[rarray.length - 1 - i];
}
return finalvalue;
}

public String reverseWords(String s) {
String reversedWords = "";
if(s.length()<=0) {
return reversedWords;
}else if(s.length() == 1){
if(s == " "){
return "";
}
return s;
}
char arr[] = s.toCharArray();
int j = arr.length-1;
while(j >= 0 ){
if( arr[j] == ' '){
reversedWords+=arr[j];
}else{
String temp="";
while(j>=0 && arr[j] != ' '){
temp+=arr[j];
j--;
}
j++;
temp = reverseWord(temp);
reversedWords+=temp;
}
j--;
}
String[] chk = reversedWords.split(" ");
if(chk == null || chk.length == 0){
return "";
}
return reversedWords;
}
public String reverseWord(String s){
char[] arr = s.toCharArray();
for(int i=0,j=arr.length-1;i<=j;i++,j--){
char tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
return String.valueOf(arr);
}

public static void main(String[] args) {
String str = "Prashant";
int len = str.length();
char[] c = new char[len];
for (int j = len - 1, i = 0; j >= 0; j--, i++) {
c[i] = str.charAt(j);
}
str = String.copyValueOf(c);
System.out.println(str);
}

public void reverString(){
System.out.println("Enter value");
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
try{
String str=br.readLine();
char[] charArray=str.toCharArray();
for(int i=charArray.length-1; i>=0; i--){
System.out.println(charArray[i]);
}
}
catch(IOException ex){
}

recursion:
public String stringReverse(String string) {
if (string == null || string.length() == 0) {
return string;
}
return stringReverse(string.substring(1)) + string.charAt(0);
}

Sequence of characters (or) StringString's Family:
String testString = "Yashwanth#777"; // ~1 1⁄4→D800₁₆«2²⁰
Using Java 8 Stream API
First we convert String into stream by using method CharSequence.chars(), then we use the method IntStream.range to generate a sequential stream of numbers. Then we map this sequence of stream into String.
public static String reverseString_Stream(String str) {
IntStream cahrStream = str.chars();
final int[] array = cahrStream.map( x -> x ).toArray();
int from = 0, upTo = array.length;
IntFunction<String> reverseMapper = (i) -> ( Character.toString((char) array[ (upTo - i) + (from - 1) ]) );
String reverseString = IntStream.range(from, upTo) // for (int i = from; i < upTo ; i++) { ... }
.mapToObj( reverseMapper ) // array[ lastElement ]
.collect(Collectors.joining()) // Joining stream of elements together into a String.
.toString(); // This object (which is already a string!) is itself returned.
System.out.println("Reverse Stream as String : "+ reverseString);
return reverseString;
}
Using a Traditional for Loop
If you want to reverse the string then we need to follow these steps.
Convert String into an Array of Characters.
Iterate over an array in reverse order, append each Character to temporary string variable until the last character.
public static String reverseString( String reverse ) {
if( reverse != null && reverse != "" && reverse.length() > 0 ) {
char[] arr = reverse.toCharArray();
String temp = "";
for( int i = arr.length-1; i >= 0; i-- ) {
temp += arr[i];
}
System.out.println("Reverse String : "+ temp);
}
return null;
}
Easy way to Use reverse method provided form StringBuffer or StringBuilder Classes
StringBuilder and StringBuffer are mutable sequence of characters. That means one can change the value of these object's.
StringBuffer buffer = new StringBuffer(str);
System.out.println("StringBuffer - reverse : "+ buffer.reverse() );
String builderString = (new StringBuilder(str)).reverse().toString;
System.out.println("StringBuilder generated reverse String : "+ builderString );
StringBuffer has the same methods as the StringBuilder, but each method in StringBuffer is synchronized so it is thread safe.

public static String revString(String str){
char[] revCharArr = str.toCharArray();
for (int i=0; i< str.length()/2; i++){
char f = revCharArr[i];
char l = revCharArr[str.length()-i-1];
revCharArr[i] = l;
revCharArr[str.length()-i-1] = f;
}
String revStr = new String(revCharArr);
return revStr;
}

Simple For loop in java
public void reverseString(char[] s) {
int length = s.length;
for (int i = 0; i < s.length / 2; i++) {
// swaping character
char temp = s[length - i - 1];
s[length - i - 1] = s[i];
s[i] = temp;
}
}

Reverseing a string in java [duplicate]

I have "Hello World" kept in a String variable named hi.
I need to print it, but reversed.
How can I do this? I understand there is some kind of a function already built-in into Java that does that.
Related: Reverse each individual word of “Hello World” string with Java

You can use this:
new StringBuilder(hi).reverse().toString()
StringBuilder was added in Java 5. For versions prior to Java 5, the StringBuffer class can be used instead — it has the same API.

For Online Judges problems that does not allow StringBuilder or StringBuffer, you can do it in place using char[] as following:
public static String reverse(String input){
char[] in = input.toCharArray();
int begin=0;
int end=in.length-1;
char temp;
while(end>begin){
temp = in[begin];
in[begin]=in[end];
in[end] = temp;
end--;
begin++;
}
return new String(in);
}

public static String reverseIt(String source) {
int i, len = source.length();
StringBuilder dest = new StringBuilder(len);
for (i = (len - 1); i >= 0; i--){
dest.append(source.charAt(i));
}
return dest.toString();
}
http://www.java2s.com/Code/Java/Language-Basics/ReverseStringTest.htm

String string="whatever";
String reverse = new StringBuffer(string).reverse().toString();
System.out.println(reverse);

I am doing this by using the following two ways:
Reverse string by CHARACTERS:
public static void main(String[] args) {
// Using traditional approach
String result="";
for(int i=string.length()-1; i>=0; i--) {
result = result + string.charAt(i);
}
System.out.println(result);
// Using StringBuffer class
StringBuffer buffer = new StringBuffer(string);
System.out.println(buffer.reverse());
}
Reverse string by WORDS:
public static void reverseStringByWords(String string) {
StringBuilder stringBuilder = new StringBuilder();
String[] words = string.split(" ");
for (int j = words.length-1; j >= 0; j--) {
stringBuilder.append(words[j]).append(' ');
}
System.out.println("Reverse words: " + stringBuilder);
}

Take a look at the Java 6 API under StringBuffer
String s = "sample";
String result = new StringBuffer(s).reverse().toString();

Here is an example using recursion:
public void reverseString() {
String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
String reverseAlphabet = reverse(alphabet, alphabet.length()-1);
}
String reverse(String stringToReverse, int index){
if(index == 0){
return stringToReverse.charAt(0) + "";
}
char letter = stringToReverse.charAt(index);
return letter + reverse(stringToReverse, index-1);
}

Here is a low level solution:
import java.util.Scanner;
public class class1 {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
String inpStr = in.nextLine();
System.out.println("Original String :" + inpStr);
char temp;
char[] arr = inpStr.toCharArray();
int len = arr.length;
for(int i=0; i<(inpStr.length())/2; i++,len--){
temp = arr[i];
arr[i] = arr[len-1];
arr[len-1] = temp;
}
System.out.println("Reverse String :" + String.valueOf(arr));
}
}

I tried, just for fun, by using a Stack. Here my code:
public String reverseString(String s) {
Stack<Character> stack = new Stack<>();
StringBuilder sb = new StringBuilder();
for (int i = 0; i < s.length(); i++) {
stack.push(s.charAt(i));
}
while (!stack.empty()) {
sb.append(stack.pop());
}
return sb.toString();
}

Since the below method (using XOR) to reverse a string is not listed, I am attaching this method to reverse a string.
The Algorithm is based on :
1.(A XOR B) XOR B = A
2.(A XOR B) XOR A = B
Code snippet:
public class ReverseUsingXOR {
public static void main(String[] args) {
String str = "prateek";
reverseUsingXOR(str.toCharArray());
}
/*Example:
* str= prateek;
* str[low]=p;
* str[high]=k;
* str[low]=p^k;
* str[high]=(p^k)^k =p;
* str[low]=(p^k)^p=k;
*
* */
public static void reverseUsingXOR(char[] str) {
int low = 0;
int high = str.length - 1;
while (low < high) {
str[low] = (char) (str[low] ^ str[high]);
str[high] = (char) (str[low] ^ str[high]);
str[low] = (char) (str[low] ^ str[high]);
low++;
high--;
}
//display reversed string
for (int i = 0; i < str.length; i++) {
System.out.print(str[i]);
}
}
}
Output:
keetarp

As others have pointed out the preferred way is to use:
new StringBuilder(hi).reverse().toString()
But if you want to implement this by yourself, I'm afraid that the rest of responses have flaws.
The reason is that String represents a list of Unicode points, encoded in a char[] array according to the variable-length encoding: UTF-16.
This means some code points use a single element of the array (one code unit) but others use two of them, so there might be pairs of characters that must be treated as a single unit (consecutive "high" and "low" surrogates).
public static String reverseString(String s) {
char[] chars = new char[s.length()];
boolean twoCharCodepoint = false;
for (int i = 0; i < s.length(); i++) {
chars[s.length() - 1 - i] = s.charAt(i);
if (twoCharCodepoint) {
swap(chars, s.length() - 1 - i, s.length() - i);
}
twoCharCodepoint = !Character.isBmpCodePoint(s.codePointAt(i));
}
return new String(chars);
}
private static void swap(char[] array, int i, int j) {
char temp = array[i];
array[i] = array[j];
array[j] = temp;
}
public static void main(String[] args) throws Exception {
FileOutputStream fos = new FileOutputStream("C:/temp/reverse-string.txt");
StringBuilder sb = new StringBuilder("Linear B Syllable B008 A: ");
sb.appendCodePoint(65536); //http://unicode-table.com/es/#10000
sb.append(".");
fos.write(sb.toString().getBytes("UTF-16"));
fos.write("\n".getBytes("UTF-16"));
fos.write(reverseString(sb.toString()).getBytes("UTF-16"));
}

Using charAt() method
String name = "gaurav";
String reversedString = "";
for(int i = name.length()-1; i>=0; i--){
reversedString = reversedString + name.charAt(i);
}
System.out.println(reversedString);
Using toCharArray() method
String name = "gaurav";
char [] stringCharArray = name.toCharArray();
String reversedString = "";
for(int i = stringCharArray.length-1; i>=0; i--) {
reversedString = reversedString + stringCharArray[i];
}
System.out.println(reversedString);
Using reverse() method of the Stringbuilder
String name = "gaurav";
String reversedString = new StringBuilder(name).reverse().toString();
System.out.println(reversedString);
Check https://coderolls.com/reverse-a-string-in-java/

It is very simple in minimum code of lines
public class ReverseString {
public static void main(String[] args) {
String s1 = "neelendra";
for(int i=s1.length()-1;i>=0;i--)
{
System.out.print(s1.charAt(i));
}
}
}

This did the trick for me
public static void main(String[] args) {
String text = "abcdefghijklmnopqrstuvwxyz";
for (int i = (text.length() - 1); i >= 0; i--) {
System.out.print(text.charAt(i));
}
}

1. Using Character Array:
public String reverseString(String inputString) {
char[] inputStringArray = inputString.toCharArray();
String reverseString = "";
for (int i = inputStringArray.length - 1; i >= 0; i--) {
reverseString += inputStringArray[i];
}
return reverseString;
}
2. Using StringBuilder:
public String reverseString(String inputString) {
StringBuilder stringBuilder = new StringBuilder(inputString);
stringBuilder = stringBuilder.reverse();
return stringBuilder.toString();
}
OR
return new StringBuilder(inputString).reverse().toString();

System.out.print("Please enter your name: ");
String name = keyboard.nextLine();
String reverse = new StringBuffer(name).reverse().toString();
String rev = reverse.toLowerCase();
System.out.println(rev);
I used this method to turn names backwards and into lower case.

One natural way to reverse a String is to use a StringTokenizer and a stack. Stack is a class that implements an easy-to-use last-in, first-out (LIFO) stack of objects.
String s = "Hello My name is Sufiyan";
Put it in the stack frontwards
Stack<String> myStack = new Stack<>();
StringTokenizer st = new StringTokenizer(s);
while (st.hasMoreTokens()) {
myStack.push(st.nextToken());
}
Print the stack backwards
System.out.print('"' + s + '"' + " backwards by word is:\n\t\"");
while (!myStack.empty()) {
System.out.print(myStack.pop());
System.out.print(' ');
}
System.out.println('"');

public String reverse(String s) {
String reversedString = "";
for(int i=s.length(); i>0; i--) {
reversedString += s.charAt(i-1);
}
return reversedString;
}

public class Test {
public static void main(String args[]) {
StringBuffer buffer = new StringBuffer("Game Plan");
buffer.reverse();
System.out.println(buffer);
}
}

All above solution is too good but here I am making reverse string using recursive programming.
This is helpful for who is looking recursive way of doing reverse string.
public class ReversString {
public static void main(String args[]) {
char s[] = "Dhiral Pandya".toCharArray();
String r = new String(reverse(0, s));
System.out.println(r);
}
public static char[] reverse(int i, char source[]) {
if (source.length / 2 == i) {
return source;
}
char t = source[i];
source[i] = source[source.length - 1 - i];
source[source.length - 1 - i] = t;
i++;
return reverse(i, source);
}
}

You can also try this:
public class StringReverse {
public static void main(String[] args) {
String str = "Dogs hates cats";
StringBuffer sb = new StringBuffer(str);
System.out.println(sb.reverse());
}
}

Procedure :
We can use split() to split the string .Then use reverse loop and add the characters.
Code snippet:
class test
{
public static void main(String args[])
{
String str = "world";
String[] split= str.split("");
String revers = "";
for (int i = split.length-1; i>=0; i--)
{
revers += split[i];
}
System.out.printf("%s", revers);
}
}
//output : dlrow

It gets the value you typed and returns it reversed ;)
public static String reverse (String a){
char[] rarray = a.toCharArray();
String finalvalue = "";
for (int i = 0; i < rarray.length; i++)
{
finalvalue += rarray[rarray.length - 1 - i];
}
return finalvalue;
}

public String reverseWords(String s) {
String reversedWords = "";
if(s.length()<=0) {
return reversedWords;
}else if(s.length() == 1){
if(s == " "){
return "";
}
return s;
}
char arr[] = s.toCharArray();
int j = arr.length-1;
while(j >= 0 ){
if( arr[j] == ' '){
reversedWords+=arr[j];
}else{
String temp="";
while(j>=0 && arr[j] != ' '){
temp+=arr[j];
j--;
}
j++;
temp = reverseWord(temp);
reversedWords+=temp;
}
j--;
}
String[] chk = reversedWords.split(" ");
if(chk == null || chk.length == 0){
return "";
}
return reversedWords;
}
public String reverseWord(String s){
char[] arr = s.toCharArray();
for(int i=0,j=arr.length-1;i<=j;i++,j--){
char tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
return String.valueOf(arr);
}

public static void main(String[] args) {
String str = "Prashant";
int len = str.length();
char[] c = new char[len];
for (int j = len - 1, i = 0; j >= 0; j--, i++) {
c[i] = str.charAt(j);
}
str = String.copyValueOf(c);
System.out.println(str);
}

public void reverString(){
System.out.println("Enter value");
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
try{
String str=br.readLine();
char[] charArray=str.toCharArray();
for(int i=charArray.length-1; i>=0; i--){
System.out.println(charArray[i]);
}
}
catch(IOException ex){
}

recursion:
public String stringReverse(String string) {
if (string == null || string.length() == 0) {
return string;
}
return stringReverse(string.substring(1)) + string.charAt(0);
}

Sequence of characters (or) StringString's Family:
String testString = "Yashwanth#777"; // ~1 1⁄4→D800₁₆«2²⁰
Using Java 8 Stream API
First we convert String into stream by using method CharSequence.chars(), then we use the method IntStream.range to generate a sequential stream of numbers. Then we map this sequence of stream into String.
public static String reverseString_Stream(String str) {
IntStream cahrStream = str.chars();
final int[] array = cahrStream.map( x -> x ).toArray();
int from = 0, upTo = array.length;
IntFunction<String> reverseMapper = (i) -> ( Character.toString((char) array[ (upTo - i) + (from - 1) ]) );
String reverseString = IntStream.range(from, upTo) // for (int i = from; i < upTo ; i++) { ... }
.mapToObj( reverseMapper ) // array[ lastElement ]
.collect(Collectors.joining()) // Joining stream of elements together into a String.
.toString(); // This object (which is already a string!) is itself returned.
System.out.println("Reverse Stream as String : "+ reverseString);
return reverseString;
}
Using a Traditional for Loop
If you want to reverse the string then we need to follow these steps.
Convert String into an Array of Characters.
Iterate over an array in reverse order, append each Character to temporary string variable until the last character.
public static String reverseString( String reverse ) {
if( reverse != null && reverse != "" && reverse.length() > 0 ) {
char[] arr = reverse.toCharArray();
String temp = "";
for( int i = arr.length-1; i >= 0; i-- ) {
temp += arr[i];
}
System.out.println("Reverse String : "+ temp);
}
return null;
}
Easy way to Use reverse method provided form StringBuffer or StringBuilder Classes
StringBuilder and StringBuffer are mutable sequence of characters. That means one can change the value of these object's.
StringBuffer buffer = new StringBuffer(str);
System.out.println("StringBuffer - reverse : "+ buffer.reverse() );
String builderString = (new StringBuilder(str)).reverse().toString;
System.out.println("StringBuilder generated reverse String : "+ builderString );
StringBuffer has the same methods as the StringBuilder, but each method in StringBuffer is synchronized so it is thread safe.

public static String revString(String str){
char[] revCharArr = str.toCharArray();
for (int i=0; i< str.length()/2; i++){
char f = revCharArr[i];
char l = revCharArr[str.length()-i-1];
revCharArr[i] = l;
revCharArr[str.length()-i-1] = f;
}
String revStr = new String(revCharArr);
return revStr;
}

Simple For loop in java
public void reverseString(char[] s) {
int length = s.length;
for (int i = 0; i < s.length / 2; i++) {
// swaping character
char temp = s[length - i - 1];
s[length - i - 1] = s[i];
s[i] = temp;
}
}

plusOut code java

I'm trying to write a code that will give this output:
plusOut("12xy34", "xy") → "++xy++"
it returns a string where the characters in the original have been replaced by + except for where the 2nd string appears in the first string, but im having problems with my code. Here it is:
public String plusOut(String str, String word) {
String newString = "";
for (int i=0; i<str.length()-1; i++) {
if (str.substring(i, word.length()).equals(word)) {
newString = newString + str.substring(i, word.length());
}
else {
newString = newString + "+";
}
}
return newString;
}

There are some bugs in your code, see the comments.
public String plusOut(String str, String word) {
String newString = "";
// iterate up to length() to catch the last char if word.length() is 1
for (int i = 0; i < str.length(); i++) {
// use min() to avoid an IndexOutOfRange
String sub = str.substring(i, Math.min(i+word.length(), str.length()));
if (sub.equals(word)) {
newString = newString + sub;
// skip remaining characters of word
i += sub.length()-1;
}
else {
newString = newString + "+";
}
}
return newString;
}
In addition to that, I'd use a StringBuilder instead of the + operator.

You should really tell us what specific problems you are facing with your current code. In any case, here's how I would do it:
Split str on all occurrences of word to form a String[].
Loop through this array and append a number of '+' characters to newString corresponding to the length of whatever element of the array you're on.
On the same loop iteration, append word to newString, unless of course you're on the last element of the array.
This is what I mean:
public static String plusOut(String str, String word) {
StringBuilder newString = new StringBuilder(str.length());
String[] split = str.split(word);
for (int i = 0; i < split.length; i++) {
for (int j = 0; j < split[i].length(); j++)
newString.append('+');
if (i != split.length - 1)
newString.append(word);
}
return newString.toString();
}
Oh and just another tip: try to avoid appending to strings repeatedly within a loop. If you need to, use a StringBuilder instead.
System.out.println(plusOut("12xy34", "xy"));
++xy++

The best and simplest way I can think of is to use regular expressions and do a replaceAll.
General idea will be to get the second character build an regex with that and replaceAll with the regular expression and the replacement character.
public String plusOut(String str, String word) {
String regEx="[^"+Pattern.quote(word)+"]";
str.replaceAll(regEx,"+");
}
Note that the Pattern.quote() will make sure that your word won't screw the regex.
I didn't try out the code, but it should work without a problem.

This will do that for you.
public String plusOut(String str, String word) {
if(!str.contains(word)){
System.out.println("Word not found in string!");
return "Ut-oh!";
}
int indexOfStart = str.indexOf(word);
StringBuilder sb = new StringBuilder();
for(int i = 0; i<indexOfStart; i++){
sb.append('+');
}
sb.append(word);
for(int i=indexOfStart+word.length(); i < str.length(); i++){
sb.append('+');
}
return sb.toString();
}

So many answers! Well, here's mine as well:
public static String plusOut(String str, String word) {
String output = "";
int index = str.indexOf(word); // if -1 is returned, replace all chars
for (int i= 0; i < str.length(); i++) {
if(i == index)
{
output += word;
i += word.length() -1; // because i++ will still occurr
continue;
}
output += "+";
}
return output;
}
and test code in main:
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
String test = "somethinghello12345.1!#";
System.out.println(test + " -> " + plusOut(test, "hello"));
test = "somethinghello12345.1!#";
System.out.println(test + " -> " + plusOut(test, "not gonna work"));
}
will produce the ouput:
somethinghello12345.1!# -> +++++++++hello+++++++++
somethinghello12345.1!# -> +++++++++++++++++++++++

Try this :
public static String plusOut(String word, String find) {
StringBuilder newStr = new StringBuilder();
int start = word.indexOf(find);
if (start > -1) {
for (int i = 0; i < start; i++) {
newStr.append("+");
}
newStr.append(find);
for (int i = 0; i < word.length() - (start + find.length()); i++) {
newStr.append("+");
}
}
return newStr;
}

We Keep Coding

Java is a programming language and computing platform first released by Sun Microsystems in 1995.

Removing characters from string efficiently - java

Use word = word.replaceAll("[,.;\\-()]", ""); Note that special character - (hyphen) should be escaped by double backslashes, because otherwise it is considered to construct a range.

Although no more efficient than the original replace technique you could use word = word.replaceAll("\\p{Punct}+", ""); to use a simple expression using replaceAll with a wider range of characters replaced

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plusOut code java

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