I have here a method that displays a string backward.
public static String ReverseStr(String backward) {
String newString = "";
for (int i=0; i<backward.length(); i++) {
newString = backward.charAt(i) + newString;
}
return newString;
}
It works properly but I'd like to do it in another way, that is, using a for loop, getting each character in the string using substring method with two parameters, starting with the last character then concatenates that one-character substring with the new string each time through the loop.
I tried this:
public static String ReverseStr(String backward) {
String newString = "";
for (int i=0; i>backward.length(); i--) {
String subChar = backward.substring(backward.length()-1);
newString += subChar;
}
return newString;
}
But when I run the program, it displays nothing. Please help me fix the code. Thank you very much!
If this is not a homework, then use StringBuilder class and reverse() method.
http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/StringBuilder.html#reverse()
If this is a homework do it by yourself.
The loop never executes due to wrong control condition:
for (int i=0; i>backward.length(); i--)
It starts from 0 and continues until i is greater than length (which is never true as length is always at least 0). You probably meant:
for (int i=backward.length(); i>=0; i--)
Once you manage to fix your code, consider using StringBuilder instead of concatenating to String. And once you manage to use StringBuilder, you'll discover handy reverse() method:
return new StringBuilder(backward).reverse().toString();
Your for loop is messed up, it will never run since you have the wrong condition, change it to:
for (int i=backward.length(); i>=0; i--)
class Test
{
public static void main(String[] args)
{
String strtorev = "Test Code";
String newString = "";
int len = strtorev.length();
System.out.println(len);
for(int i =0;i<len;i++)
{
String subChar = strtorev.substring(strtorev.length()-1-i,strtorev.length()-i);
newString += subChar;
System.out.println(newString);
}
}
}
You should StringBuilder. The following code should work as you expect.
public static String ReverseStr(String backward)
{
String newString = "";
StringBuilder sb=new StringBuilder(backward);
for (int i=0; i>backward.length(); i--) //backward.length() may be replaced with sb.length()
{
String subChar = sb.charAt(i); //Replace `substring()` with `charAt()`
newString += subChar;
}
return newString;
}
public static String ReverseStr(String backward) {
String newString = "";
for (int i=backward.length()-1; i>=0; i--)
newString+ = backward.charAt(i);
return newString;
}
We can use recursion to reverse a String
public class ReverseStringTest {
public static String reverseString(String str) {
if (str.isEmpty()) {
return str;
}
//Calling Function Recursively
return reverseString(str.substring(1)) + str.charAt(0);
}
public static void main(String[] args) {
System.out.println(reverseString("java"));
}
}
Related
I have written a piece of code to reverse a string in Java. However, its showing multiple errors and I wish to understand where it is that I am going wrong. I know that there are alternative methods of reversing a string. However, I want to know where I am going wrong with my code.
public class RevString {
public static void main(String[] args)
{
public Reverse (String str)
{
int len = str.length();
String rev;
for (int i = 0; i <= len; i++)
{
rev = str[i] + rev;
}
System.out.println(rev);
}
Reverse("Canyon");
}
}
Errors:
Multiple markers at this line
- Syntax error on token ")", ; expected
- Syntax error on token "(", . expected
- Reverse cannot be resolved to a type
- Illegal modifier for parameter str; only final is
The method Reverse(String) is undefined for the type
RevString
Could someone provide me with a resolution?
There are many errors in your code :
For loop condition should be i < len
String rev should be initialized to "" (empty string), else it will throw error when you try to append another string to it.
You can't access characters in a string using str[i], use str.charAt(i) instead.
You are trying to initialize a function (Reverse) inside another function (main), you must initialize it outside the main function.
Also, here is a simple one liner for string reversal:
new StringBuilder(str).reverse().toString()
A good tip might be to use the StringBuilder class whenever you want to do any kind of string manipulation in Java.
Your code has many issues:
You are declaring the method Reverse() inside the main method.
You also need to initialize rev to an empty string.
You can use str.charAt(i) to access each character of the string.
Your for loop goes beyond the string if you use i <= len; so it
should be i < len;.
Your Reverse() method should be static since you are calling it in main
method (which is static)
Here is working code.
public class RevString {
public static void main(String[] args) {
Reverse("Canyon");
}
public static void Reverse (String str) {
int len = str.length();
String rev="";
for (int i = 0; i < len; i++) {
rev = str.charAt(i) + rev;
}
System.out.println(rev);
}
}
Please see the below code:
public class Hello {
public static String reverse (String str){
int len = str.length();
String rev="";
char[] strArray = str.toCharArray();
for (int i = 0; i < len; i++)
{
rev = strArray[i] + rev;
}
return rev;
}
public static void main(String[] args) {
String result = reverse("Canyon");
System.out.println("Reversed String: " + result);
}
}
public class reverseString
{
public static void main(String[] args)
{
System.out.println("Welcome to the the string reverser.");
System.out.println("Here is where a person may put is a sentence and the orintation" +
" of the words is reversed.");
Scanner keyboard = new Scanner(System.in);
String word = keyboard.nextLine();
int lengthOf = word.length();
int j = 0;
char loopStr;
String LoopStr;
String Nstr = "";
for(int n = lengthOf; n >0 ;n--)
{
j = n;
LoopStr = word.substring(j-1,j);
Nstr = Nstr + LoopStr;
}
System.out.println(Nstr);
}
}
Need to create a method in which, given a string, a new string will be made and returned formed out of every other character in the original string.
public static String everyOther(String str) {
String result = "";
for (int i=0; i<A.length; i+=2){
result = result + str.charAt(i);
}
System.out.println(result);
return result;
}
public static void main(String[] args) {
String G = "abcdefghijklmnopqrstuvwxyz";
System.out.println(everyOther(G));
}
Your everyOther method should read
public static String everyOther(String str) {
String result = "";
for (int i=0; i < str.length(); i+=2){
result += str.charAt(i);
}
return result;
}
Your for loop was slightly off (see my comment on OP), and there is no need to print out your result ehre as you do that in your main function - unless ofcourse you wanted to print it out twice
I'm trying to create a method that will accept 2 strings as arguments. The first string will be a phrase, the second also a prhase. What I want the method to do is to compare both strings for matching chars. If string 2 has a char that is found in string 1 then replace string 2's instance of the char with an underscore.
Example:
This is the input:
phrase1 = "String 1"
phrase2 = "Strone 2"
The output string is called newPhrase and it will have the string built from the underscores:
newPhrase = "___one 2"
Its not working for me I am doing something wrong.
public class DashedPhrase
{
public static void main(String[] args)
{
dashedHelp("ABCDE","ABDC");
}
public static String dashedHelp(String phrase1, String phrase2)
{
String newPhrase = "_";
for(int i = 0; i < phrase.length(); i++)
{
if(phrase.charAt(i) == phrase2.charAt(i))
{
newPhrase.charAt(i) += phrase2.charAt(i);
}
}
System.out.print(newPhrase);
return newPhrase;
}
}
To make it easier for you to understand, you can use StringBuilder and its method setCharAt().
Notice the i < phrase1.length() && i < phrase2.length() in the condition for the for loop. This is to make sure you don't get any ArrayIndexOutOfBounds exception.
public static void main(String[] args)
{
System.out.println("ABCDE");
System.out.println("ABDC");
dashedHelp("ABCDE","ABDC");
System.out.println();
System.out.println();
System.out.println("String 1");
System.out.println("Strone 2");
String phrase1 = "String 1";
String phrase2 = "Strone 2";
dashedHelp(phrase1, phrase2);
}
public static String dashedHelp(String phrase1, String phrase2)
{
StringBuilder newPhrase = new StringBuilder(phrase1);
for(int i = 0; i < phrase1.length() && i < phrase2.length(); i++)
{
if(phrase1.charAt(i) == phrase2.charAt(i))
{
newPhrase.setCharAt(i, '_');
}
}
System.out.print(newPhrase);
return newPhrase.toString();
}
Output:
ABCDE
ABDC
__CDE
String 1
Strone 2
___i_g_1
newPhrase.charAt(i) doesn't let you replace a character, it just returns it. Java's Strings are immutable. I you want to change it you should use StringBuilder. Look into the replace(int start, int end, String str) method.
Since you need to return a string that has the same length as phrase2, you need to iterate over each character of phrase2, and replace the matching characters of both phrases. And, of course, if phrase2 is longer than phrase1, you need to include the remaining characters in the answer. You can try this:
public static String dashedHelp(String phrase1, String phrase2) {
String ans = "";
String subChar = "_";
int i;
for(i = 0; i<phrase2.length(); i++) {
if(i<phrase1.length() && phrase1.charAt(i) == phrase2.charAt(i))
ans += subChar;
else
ans += phrase2.charAt(i);
}
return ans;
}
Hope it helps
Of course, if you need to output phrase1 with underscores in the places where phrase2 has equal characters, you can interchange phrase2 with phrase1 in the above code.
Testing it
The complete class would look like this:
public class MyClass {
public static String dashedHelp(String phrase1, String phrase2) {
// The method code goes here
}
public static void main(String[] args) {
System.out.println(dashedHelp("String 1", "Strone 2"));
}
}
The output of this program is ___o_e_2. This matches (approximately) your desired output.
The code in the example won't even compile.
newPhrase.charAt(i) += phrase2.charAt(i);
That's a bad assignment. It's the same as writing
newPhrase.charAt(i) = newPhrase.charAt(i) + phrase2.charAt(i);
but the expression on the left side of the '=' isn't something to which you can properly assign a value.
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;
}
What I am trying to do, is create a method, that has a string and a character as parameters, the method then takes the string and searches for the given character. If the string contains that character, it returns an array of integers of where the character showed up. Here is what I have so far:
public class Sheet {
public static void main(String[] args) {
String string = "bbnnbb";
String complete = null;
//*******
for(int i = 0; i < string.length(); i++){
complete = StringSearch(string,'n').toString();
}
//********
}
public static int[] StringSearch(String string, char lookfor) {
int[]num = new int[string.length()];
for(int i = 0; i < num.length; i++){
if(string.charAt(i)== lookfor){
num[i] = i;
}
}
return num;
}
}
The method works fine, and returns this:
0
0
2
3
0
0
What I am trying to do, is make those into 1 string so it would look like this "002300".
Is there any possible way of doing this? I have tried to do it in the starred area of the code, but I have had no success.
just do
StringBuffer strBuff = new StringBuffer();
for(int i = 0; i<str.length(); i++)
{
if(str.charAt(i) == reqChar)
{
strBuff.append(str.charAt(i));
}
else
{
strBuff.append('0');
}
}
return str.toString();
Just add the result to the existing string with the += operator
String complete = "";
for(...)
complete += StringSearch(string,'n').toString();
I would just use java's regex library, that way it's more flexible (eg if you want to look for more than just a single character). Plus it's highly optimized.
StringBuilder positions = "";
Pattern pattern = Pattern.compile(string);
Matcher matcher = pattern.matcher(lookfor);
while(matcher.find()){
positions.append(matcher.start());
}
return positions;
Updated with StringBuilder for better practices.
public static String StringSearch(String string, char lookfor) {
StringBuilder sb = new StringBuilder();
for(int i = 0; i < string.length; i++){
if(string.charAt(i) == lookfor)
sb.append(i);
else
sb.append("0");
}
return sb.toString();
}
Then you can just call it once, without a for loop. Not sure why you call it for every character in the string.
complete = StringSearch(string,'n');