Question

This is a much simplified version of a class file I’m working on, I’ve just used these classes to show my problem.

public class Test {
    private String string1 = null;
    private String string2 = null;

    private void setString(String s) {
        s = "hello";
    }

    private void set() {
        setString(string1);
        setString(string2);
    }

    public void print() {
        System.out.println(string1);
        System.out.println(string2);
    }

    public void initialise() {
        set();
        print();
    }  
}

public class StringTest {
    public static void main(String[] args) {
        Test test = new Test();
        test.initialise();
    }
}

Anyway, basically, after this the two string variables are still null. What causes this problem? and how can I get around it? (Still learning the fundamentals of java – if that’s relevant).

Any help/guidance is greatly appreciated.

Answer 1

Your problem is that Java is pass by value, so your setString method does not do anything. To change the value of string1, you need to have string1 = xxxx; somewhere in your code. For example:

private void set() {
    string1 = getDefaultString();
    string2 = getDefaultString();
}

private String getDefaultString() {
    return "hello";
}