Unable to replace characters in a String

Question

I am trying to go through an array of characters and replace that character in the string with the parallel character in the other array.

private String replace(String input)
{
    char[] first = {'a','e','o','s'};
    char[] second = {'@','3','0','$'};
    String myCopy = input.toLowerCase();


    for(int y = 0; y < first.length; y++)
    {
        myCopy.replace(first[y],second[y]);
    }


    return myCopy;
}

Here's and example of what I get:

Enter a string: as the dog runs here
Output: as the dog runs here

It always outputs the same string with no replacements.

I also tried using:

myCopy.replace('a','@');

and

myCopy.replace("a","@");

and the replaceAll method.

Any suggestions?

Jon Skeet · Accepted Answer · 2012-03-19 15:24:41Z

12

Strings are immutable in Java. replace() doesn't change the string you call it on - it returns a new string with the changes. So you want:

myCopy = myCopy.replace(first[y], second[y]);

(The same is true for all the methods on String which "appear" to be changing it, as it's immutable.)

answered Mar 19, 2012 at 15:24

Jon Skeet

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Comments

Michał Šrajer · Accepted Answer · 2012-03-19 15:24:15Z

5

String.replace() will return a new string. Strings are immutable in java.

What you are looking for is probably StringBuilder. You can build it from string, change it as long as you need and then generate an immutable String as a result via toSting().

answered Mar 19, 2012 at 15:24

Michał Šrajer

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1 Comment

Austin Green Over a year ago

Thank you so much. So simple I never even realized it.

Perception · Accepted Answer · 2012-03-19 15:24:53Z

0

Strings are immutable. So in your for loop your operation is not having any tangible effect. You need to assign the result of replace back to the original variable:

for(int y = 0; y < first.length; y++) {
    myCopy = myCopy.replace(first[y],second[y]);
}

answered Mar 19, 2012 at 15:24

Perception

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Comments

Woot4Moo · Accepted Answer · 2012-03-19 15:24:58Z

0

The reason why this is not working is that you are not assigning the returned String value to the array. This:

     for(int y = 0; y < first.length; y++)   
  {     
    myCopy.replace(first[y],second[y]); 
    }

Needs to become:

 for(int y = 0; y < first.length; y++)   
  {     
    myCopy =  myCopy.replace(first[y],second[y]); 
    }

answered Mar 19, 2012 at 15:24

Woot4Moo

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Comments

AlexR · Accepted Answer · 2012-03-19 15:25:04Z

0

You are confused with String and replace(). String is immutable, i.e. you cannot change its state. Calling replace() creates copy of source string and returns it. Do something like this:

String replacedString = myCopy.replace(first[y],second[y]);

answered Mar 19, 2012 at 15:25

AlexR

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Comments

Igor · Accepted Answer · 2012-03-20 15:02:04Z

0

As Michal said, Strings are immutable. If this is being used in a process that is more intensive, you may want to use StringBuffer instead. StringBuffer is mutable, however it will take some additional work as it doesn't have a directly comparable replace() method.

edited Mar 20, 2012 at 15:02

Igor

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answered Mar 19, 2012 at 15:30

CodeChimp

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