Question

I want to send a string to a method and change the string there.
The method should return void.
Example:

String s = "Hello";
ChangeString(s);

String res = s;
//res = "HelloWorld"
-------------------------------------------

private void ChageString(String s){
s = s + "World";
}

How can I do it in Java?
Can it be done without adding another class?

Thanks!
PB

Answer 1

Your method cannot work with the current interface because of two reasons:

• Strings are immutable. Once you have created a string you cannot later change that string object.
• Java uses pass-by-value, not pass-by-reference. When you assign a new value to s in your method it only modifies the local s, not the original s in the calling code.

To make your method work you need to change the interface. The simplest change is to return a new string:

private String changeString(String s){
    return s + "World";
}

Then call it like this:

String s = "Hello";
String res = changeString(s);

See it working online: ideone