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Java: How to add whitespace before and after certain chars in a string

I've tried this to put white space between every '{':
String str = "t{esting";
StringBuilder sb = new StringBuilder(str);
int i;
for(i = 0; i<str.length(); i++) {
if(str.charAt(i)=='{'){
sb.insert(i, " ");
sb.insert(i+2, " ");
}
}
System.out.println(sb.toString());
}
It works fine for one '{':
t { esting
but if there are multiple '{' it does not work. for example: t{estin{g =
t { est i n{g where I want t { estin { g.
Thank you for having a look.

Simply replace every "{" by " { " like this:
String str = "t{esting";
String newStr = str.replace("{", " { ");

The following code implements the fixes suggested in Stephen C's comment
String str = "t{esting{";
StringBuilder sb = new StringBuilder(str);
for (int i = 0; i < sb.length(); i++) { // use sb.length
if (sb.charAt(i) == '{') { // check the character in sb (not str)
sb.insert(i, ' ');
sb.insert(i + 2, ' ');
i += 2; // jump over the shifted `{`
}
}
System.out.println("'" + sb.toString() + "'");
Output:
't { esting { '
However, String::replace or String::replaceAll methods are more suitable for such task.

How to swap every 2 letters in a String? - Java

So I'm currently working on a personal project and I made a program that tries to swap every 2 letter in a given string.
So I want the output like this:
(Note Input String is "abllte")
ballet
So I wrote this method
public static String codeString(String input) {
String firstLetter = "";
String secoundLetter = "";
String result = "";
for(int i = 0; i < input.length()-1; i++){
for(int c = 0; c < i; c = c +2)
{
firstLetter = input.substring(c,c + 1);
secoundLetter = input.substring(c + 1, c + 2);
}
result = result + secoundLetter + firstLetter;
}
return result;
}
But I get this output:
ababllll
Any idea how to solve this?
Thank you in advance!

You only need one loop. This works for both even and odd length character strings.
first, the methods used return the StringBuilder in its current modified state.
So sb.insert(i, sb.charAt(i+1)) inserts the char at i+1 at i
So if sb contained ab, StringBuilder would now contain bab
insert returns the modifed StringBuilder so now sb.deleteCharAt(i+2) deletes the second a (the one that was just copied).
this is then repeated until all characters are swapped.
Because of the constant inserting and deletion of characters this is not very efficient.
for (String s : new String[] { "abcdefg", "abcdefgh" }) {
StringBuilder sb = new StringBuilder(s);
for (int i = 0; i < sb.length() - 1; i += 2) {
sb.insert(i, sb.charAt(i + 1)).deleteCharAt(i + 2);
}
System.out.println(s + " -> " + sb);
}
Prints
abcdefg -> badcfeg
abcdefgh -> badcfehg
For a more efficient algorithm, this would be the way to go. It's also much more intuitive.
for (String s : new String[] { "abcdefg", "abcdefgh" }) {
char ch[] = s.toCharArray();
for (int i = 0; i < ch.length - 1; i+=2) {
char c = ch[i];
ch[i] = ch[i + 1];
ch[i + 1] = c;
}
String d = String.valueOf(ch);
System.out.println(s + " -> " + d);
}
This prints the same as above.

I'm not sure what the point of your nested for loop is. You can do this with just one loop.
public static String codeString(String input) {
String firstLetter = "";
String secoundLetter = "";
String result = "";
for(int i = 0; i < input.length()-1; i+=2){
firstLetter = input.substring(i,i+1);
secoundLetter = input.substring(i+1,i+2);
result = result + secoundLetter + firstLetter;
}
return result;
}
If your input string has an odd number of characters, you'll have to append the extra last character.
public static String codeString(String input) {
String firstLetter = "";
String secoundLetter = "";
String result = "";
for(int i = 0; i < input.length()-1; i+=2){
firstLetter = input.substring(i, i+1);
secoundLetter = input.substring(i+1, i+2);
result = result + secoundLetter + firstLetter;
}
if(input.length() % 2 == 1)
result += input.substring(input.length()-1, input.length());
return result;
}

You do not need a nested loop. Change the outer loop to step by 2 i.e. i = i + 2 and remove the inner loop.
public class Main {
public static void main(String[] args) {
System.out.println(codeString("abllte"));
}
public static String codeString(String input) {
String firstLetter = "";
String secondLetter = "";
String result = "";
for (int i = 0; i < input.length() - 1; i = i + 2) {
firstLetter = input.substring(i, i + 1);
secondLetter = input.substring(i + 1, i + 2);
result = result + secondLetter + firstLetter;
}
return result;
}
}
Output:
ballet
An alternative approach:
You can create a function with two parameters: input string as the first parameter and n as the second parameter, where every n characters in the input string need to be reversed.
public class Main {
public static void main(String[] args) {
System.out.println(codeString("abllte", 1));
System.out.println(codeString("abllte", 2));
System.out.println(codeString("abllte", 3));
System.out.println(codeString("abllte", 4));
}
public static String codeString(String input, int n) {
if (n <= input.length() / 2) {
StringBuilder result = new StringBuilder();
for (int i = 0; i < input.length() - n + 1; i = i + n) {
result.append(new StringBuilder(input.substring(i, i + n)).reverse());
}
return result.toString();
} else {
return input;
}
}
}
Output:
abllte
ballet
lbaetl
abllte

How do i Reverse Capitalize And Separate Words By Line Using String In Java?

The input is: i love cake
The output needs to be: Cake Love I
But the actual result is: I Love Cake
What I've got:
import java.util.regex.Pattern;
public class yellow {
static String reverseWords(String str){
Pattern pattern = Pattern.compile("\\s");
String[] temp = pattern.split(str);
String result = "";
for (int i = 0; i < temp.length; i++) {
if (i == temp.length - 1)
result = temp[i] + result;
else
result = " " + temp[i] + result;
}
return result;
}
public static void main(String[] args){
String source = "i love cake";
StringBuffer res = new StringBuffer();
String[] strArr = source.split(" ");
for (String str : strArr) {
char[] stringArray = str.trim().toCharArray();
stringArray[0] = Character.toUpperCase(stringArray[0]);
str = new String(stringArray);
res.append(str).append(" ");
}
System.out.print(res.toString());
}
}
What am I doing wrong?

for (String str : strArr) {
}
This loops forward. What you want is to loop backwards, or to place elements into the string backwards. I recommend you loop backwards and print as you go:
for (int i = strArr.length - 1; i >= 0; i--) {
char[] stringArray = strArr[i].trim().toCharArray();
stringArray[0] = Character.toUpperCase(stringArray[0]);
System.out.println(new String(stringArray));
}
Or, you could use that convenient reverseWords method that you never use anywhere... though looping backwards is faster. Probably.

[EDITED]
Call this for each line with string s, then print a line break (If you have multiple sentences & expect them in their own lines).
void reverseCamel(String s){
String[] ar = s.split("\\s+");
for(int i = ar.length - 1;i>=0;i--){
ar[i][0] = Character.toUpperCase(ar[i][0]);
System.out.print(ar[i] + " ");
}
}

Here is what i did.
public class Main {
public static void main(String[] args) {
reverse("I Love Cake");
}
public static void reverse( String string){
String[] word =string.split(" "); // split by spaces
int i = word.length-1;
while (i>=0){
// System.out.print(word[i].toUpperCase()+" ");//if you want in upper case
System.out.print(word[i]+" ");
i--;
}
}
}

First of all you have to reverse the String.
String[] words = source.split("\\s");
String reversedString = "";
for(int i = words.length -1; i>=0; i--){
reversedString += words[i] + " ";
}
Then, you know that the ASCII code of 'a' character is 97, 'A' is 65. To convert from lower case to capital you substract 32. All capitals are between 65 and 92. All small letters are between 97 and 124.
You want to capitalize only letters at the beginning of a word (preceded by a space or first letter).
String capitalCase = "";
for (int i = 0; i < reversedString.length(); i++) {
char c = reversedString.charAt(i);
if (c >= 97 && c <= 124) {
if (i == 0) c -= 32;
else if ((reversedString.charAt(i - 1) + "").equals(" ")) c -= 32;
}
capitalCase += c;
}
And here you go now System.out.println(capitalCase);
Overall, you will have the following code:
import java.util.Scanner;
public class yellow {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
System.out.println("Enter a string:");
String source = s.nextLine();
String[] words = source.split("\\s");
String reversedString = "";
for (int i = words.length - 1; i >= 0; i--) {
reversedString += words[i] + " ";
}
String capitalCase = "";
for (int i = 0; i < reversedString.length(); i++) {
char c = reversedString.charAt(i);
if (c >= 97 && c <= 124) {
if (i == 0) c -= 32;
else if ((reversedString.charAt(i - 1) + "").equals(" ")) c -= 32;
}
capitalCase += c;
}
System.out.println(capitalCase);
}
}
Output:
Enter a string:
i love cake
Cake Love I

Java 8 * Apache Commons Lang
public static String reverseWordsInString(String str) {
List<String> words = Pattern.compile("\\s+").splitAsStream(str)
.map(StringUtils::capitalize)
.collect(LinkedList::new, LinkedList::addFirst, (a, b) -> a.addAll(0, b));
return words.stream().collect(Collectors.joining(StringUtils.SPACE));
}
Java 8
public static String reverseWordsInString(String str) {
List<String> words = Pattern.compile("\\s+").splitAsStream(str)
.map(word -> Character.toUpperCase(word.charAt(0)) + word.substring(1).toLowerCase())
.collect(LinkedList::new, LinkedList::addFirst, (a, b) -> a.addAll(0, b));
return words.stream().collect(Collectors.joining(" "));
}

Reverse each word of a string without altering their position(Without using inbuilt fucntion)

I want to reverse each individual word of a String in Java in different different sitautions (not the entire string, just each individual word).
Example1: if input String is "This is a test" then the output should be "sihT si a tset".
Example2: if input String is "This is a test" then the output should be "sihT si a tset".
[When there is more than one space between some words]
Please also provide algorithm for understanding
What I have tried so far
class reverseAString
{
public static void main(String args[])
{
String str= "Test the product";
String strArr[]= str.split(" ");
for(int i=0;i<=strArr.length-1;i++)
{
for(int j=strArr[i].length()-1; j>=0;j--)
{
System.out.print(strArr[i].charAt(j));
}
System.out.printf(" ");
}
}
}
---------
public String reverseWordByWord(String str){
int strLeng = str.length()-1;
String reverse = "", temp = "";
for(int i = 0; i <= strLeng; i++){
temp += str.charAt(i);
if((str.charAt(i) == ' ') || (i == strLeng)){
for(int j = temp.length()-1; j >= 0; j--){
reverse += temp.charAt(j);
if((j == 0) && (i != strLeng))
reverse += " ";
}
temp = "";
}
}
return reverse;
}

This approach is much more succinct.
class StringRev{
public static void main(String args[]){
String str[] = "Test the product".split(" ");
String finalStr="";
for(int i = str.length-1; i>= 0 ;i--){
finalStr += str[i]+" ";
}
System.out.println(finalStr);
}
}

public static void main(String arg[]) {
System.out.println(reverseWords("This is a test"));
}
// function to reverse each word
public static String reverseWords(String input) {
String result = null;
StringBuffer strBuffer = new StringBuffer();
String split[] = input.split(" ");
for (String temp : split) {
if (temp != " ") {
strBuffer.append(reverse(temp));
strBuffer.append(" ");
} else {
strBuffer.append(" ");
}
}
result = strBuffer.toString();
return result;
}
// function to reverse individual word
public static String reverse(String input) {
StringBuffer strBuffer = new StringBuffer();
char[] charArray = input.toCharArray();
for (int j = charArray.length - 1; j >= 0; j--) {
strBuffer.append(charArray[j]);
}
return strBuffer.toString();
}
Split complete string on basis of space
Then convert each string to character array and reverse
individual word.

It's been a long time since I've touch Java, but here's the algorithm.
String stringToReverse = "This is a Test";
String finalString = "";
Stack word = new Stack;
for(int i = 0; i < stringToReverse.length; i++){
char chr = stringToReverse[i];
if(chr == " " || i == (stringToReverse.length - 1)){
while(word.count > 0){
finalString += word.pop();
}
finalString += chr;
}else{
word.push(chr);
}
}

Reverse a given sentence in Java

Can anyone tell me how to write a Java program to reverse a given sentence?
For example, if the input is:
"This is an interview question"
The output must be:
"question interview an is this"

You split the string by the space then iterate over it backwards to assemble the reversed sentence.
String[] words = "This is interview question".split(" ");
String rev = "";
for(int i = words.length - 1; i >= 0 ; i--)
{
rev += words[i] + " ";
}
// rev = "question interview is This "
// can also use StringBuilder:
StringBuilder revb = new StringBuilder();
for(int i = words.length - 1; i >= 0 ; i--)
{
revb.append(words[i]);
revb.append(" ");
}
// revb.toString() = "question interview is This "

String[] words = sentence.split(" ");
String[] reversedWords = ArrayUtils.reverse(words);
String reversedSentence = StringUtils.join(reversedWords, " ");
(using ArrayUtils and StringUtils from commons-lang, but these are easy methods to write - just a few loops)

Just being different: a recursive solution. Doesn't add any extra spaces.
public static String reverse(String s) {
int k = s.indexOf(" ");
return k == -1 ? s : reverse(s.substring(k + 1)) + " " + s.substring(0, k);
}
System.out.println("[" + reverse("This is interview question") + "]");
// prints "[question interview is This]"
I will also improve on the split solution by using \b instead (it's so obvious!).
String[] parts = "Word boundary is better than space".split("\\b");
StringBuilder sb = new StringBuilder();
for (int i = parts.length; i --> 0 ;) {
sb.append(parts[i]);
}
System.out.println("[" + sb.toString() + "]");
// prints "[space than better is boundary Word]"

Bozho already gave a great Java-specific answer, but in the event you ever need to solve this problem without Java API methods:
To reverse, you can simply pop individual words onto a stack and pop them all back off when there are no words left.
(Just to be extra clear, Java does provide a Stack class, so it is possible to use this method in Java as well).

Just split it on a space character into a string array, then loop over the array in reverse order and construct the output string.
String input = "This is interview question";
String output = "";
String[] array = input.split(" ");
for(int i = array.length-1; i >= 0; i--)
{
output += array[i];
if (i != 0) { output += " "; }
}

a every boring bit of java:
List<String> l = new ArrayList<String>(Arrays.asList("this is an interview question".split("\\s")));
Collections.reverse(l);
StringBuffer b = new StringBuffer();
for( String s : l ){
b.append(s).append(' ');
}
b.toString().trim();
in groovy it's a little bit more readable:
"this is an interview question"
.split("\\s")
.reverse()
.join(' ')

I also give it a try: Here's a version using a stack and a scanner:
String input = "this is interview question";
Scanner sc = new Scanner(input);
Stack<String> stack = new Stack<String>();
while(sc.hasNext()) {
stack.push(sc.next());
}
StringBuilder output = new StringBuilder();
for(;;) { // forever
output.append(stack.pop());
if(stack.isEmpty()) {
break; // end loop
} else {
output.append(" ");
}
}

public class ReverseString {
public void reverse(String[] source) {
String dest = "";
for (int n = source.length - 1; n >= 0; n--) {
dest += source[n] + " ";
}
System.out.println(dest);
}
public static void main(String args[]) {
ReverseString rs = new ReverseString();
String[] str = "What is going on".split(" ");
rs.reverse(str);
}
}

nicer approach probably.. had seen the logic somewhere..here is my code which might do the job.
public class revWords {
public static void main(String[] args) {
revWords obj = new revWords();
String print = obj.reverseWords("I am God");
System.out.println(print);
}
public String reverseWords(String words)
{
if(words == null || words.isEmpty() || !words.contains(" "))
return words;
String reversed = "";
for( String word : words.split(" "))
reversed = word + " " + reversed;
return reversed;
}
}

I don't think you should use any library..
1) Reverse whole string
2) Reverse each word.
public static void revWord(char[] a) {
// reverse whole
revWord(a, 0, a.length);
int st = -1;
int end = -1;
for (int i = 0; i < a.length; i++) {
if (st == -1 && a[i] != ' ') {
st = i;
}
if (end == -1 && a[i] == ' ' ) {
end = i;
}
if(i == a.length-1){
end=i+1;
}
if (st != -1 && end != -1) {
revWord(a, st, end );
st = -1;
end = -1;
}
}
}
public static void revWord(char[] a, int s, int l) {
int mid = (l - s) / 2;
l--;
for (int i = 0; i < mid; i++, l--) {
char t = a[s+i];
a[s+i] = a[l];
a[l] = t;
}
}
`

No one has mentioned a vanilla Java 8 based solution yet, which is the same as Bozho's, but without any third-party libraries. So here it is:
String input = "This is interview question";
List<String> list = Arrays.asList(input.split(" "));
Collections.reverse(list);
System.out.println(list.stream().collect(Collectors.joining(" ")));

please try below solution, this is working for me.
public class reverseline {
public static void main(String[] args) {
// TODO Auto-generated method stub
String str="This is interview question";
String words[]=str.split(" ");
for(int i=words.length-1;i>=0;i--){
System.out.print(words[i]+" ");
}
}
}

Before StringTokenizer was declared legacy, many used StringTokenizer for this. Thought I would just leave it here.
String sentence = "This is interview question";
String reversed = "";
StringTokenizer tokens = new StringTokenizer(sentence);
while (tokens.hasMoreTokens()) { // Loop through each token
reversed = tokens.nextToken() + ' ' + reversed; //add to start
}
System.out.println(reversed.trim());

Shortest Answer
public class ReverseSentence {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter a sentence");
String inputString = sc.nextLine();
String[] words = inputString.split(" ");
List<String> reverseWord = Arrays.asList(words);
Collections.reverse(reverseWord);
Iterator itr = reverseWord.iterator();
while (itr.hasNext()) {
System.out.print(itr.next() + " ");
}
}
}
OR
public class ReverseSentence {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter a sentence");
String inputString = sc.nextLine();
String[] words = inputString.split(" ");
for (int i = words.length-1 ; i >= 0; i--) {
System.out.print(words[i] +" ");
}
}
}