JAVA replacing a String without replacing it many times

Question

String _p = p;      
for(int i = 0; i <= _p.length()-1; i++)
   _p = _p.replace(lChar[_p.charAt(i)].getText(), tReplace[_p.charAt(i)].getText());
tOut.append(_p);

Above is the code I use to replace a string which I read out of a TextArea (tIn -> p), then there is a Label Array (lChar) where I store every unique char (the char value is the Array index) and I have also a TextField Array (tReplace) here I write the replace string (which can be multiple chars) for every char in lChar (the char value from the 'old' char is the Array index).

So now I want to replace every char in lChar with every char in tReplace. If i want to replace '1' with '2' and '2' with '1' for the string '12' I get '11', because in the first loop it changes it to '22' and in the next loop it changes it to '11'. BUT I only want to change every letter once as if i would write

String.valueOf(21).replace("2","1").replace("1","2");

Any ideas how to do this?

amit · Accepted Answer · 2011-04-17 13:25:32Z

you can create an automaton for this task:
cast your String to char[] using String.getChars() and then iterate over the array, replace each char as desired.
note: if you need to replace each char with a string which its length is >1, you can use the same approach, but instead using a char[], use a StringBuilder, and for each char: if it needs to be replaced, append the replacing-string to the StringBuilder, else: append the char to the StringBuilder
sample code:

String original = "1212";
        HashMap<Character, String> map = new HashMap<Character, String>();
        map.put('1', "22");
        map.put('2', "1");
        StringBuilder sb = new StringBuilder();
        for (int i =0;i<original.length();i++) {
            char ch = original.charAt(i);
            if (map.containsKey(ch)) {
                sb.append(map.get(ch));
            } else {
                sb.append(ch);
            }
        }
        System.out.println(sb);

will result in: 221221

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