How to replace slash with underscore [duplicate]

Question

Possible Duplicate:
Hints for java.lang.String.replace problem?
Using string.replace() in Java

Why "/" does not replaced by "_" ?

public static void main(String[] args) throws IOException {
    String file = "A/B";
    file.replaceAll("/", "_");
    System.out.println(file);
}

Answer 1

Because instances of java.lang.String are immutable^*. replaceAll returns the correct string, but your program throws it away. Change your program as follows to correct the issue:

file = file.replaceAll("/", "_");

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^* That's a fancy way of saying "non-changeable": once a string instance "A/B" is created, there are no methods that you could call on it to change that value.

Answer 2

You need to store the result of the file.replaceAll() call as String instances are immutable:

file = file.replaceAll("/", "_");