How to replace a substring of a string

You need to use return value of replaceAll() method. replaceAll() does not replace the characters in the current string, it returns a new string with replacement.

  • String objects are immutable, their values cannot be changed after they are created.
  • You may use replace() instead of replaceAll() if you don’t need regex.
    String str = "abcd=0; efgh=1";
    String replacedStr = str.replaceAll("abcd", "dddd");

    System.out.println(str);
    System.out.println(replacedStr);

outputs

abcd=0; efgh=1
dddd=0; efgh=1

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