java beginner- is an arraylist call by reference

Question

In a java program, I want 3 arraylist variables to be modified by a call to a single function.

Am I correct in thinking that if I pass these 3 arraylists as parameters to that function, then all 3 can be modified within the function? Or will I have to modify each arraylist in a separate function, and specify that array list as the return value, to ensure that it is modified.

Answer 1

Am I correct in thinking that if I pass these 3 arraylists as parameters to that function, then all 3 can be modified within the function?

In a word, yes.

It is worth noting that the "by reference" terminology in the title of your question is not exactly right. In Java, everything is passed by value , including object references. It is the fact that the three ArrayList parameters are references themselves that makes any changes made to the lists propagate back to the caller.

Answer 2

Yes, you can pass the 3 ArrayList s as parameters to the method. They are treated like any other object.

As to whether to return another ArrayList , this depends a lot on what the method has to do.

Answer 3

The following code works like "call by reference":

package arrayList;

import java.util.ArrayList;

public class CallByValueReference {

class myObject {
    String str;

    public myObject(String str) {
        super();
        this.str = str;
    }

    public String getStr() {
        return str;
    }

    public void setStr(String str) {
        this.str = str;
    }

    @Override
    public String toString() {
        return "myObject [str=" + str + "]";
    }   
}

ArrayList<myObject> strArray = new ArrayList<myObject>();

public static void main(String[] args) {
    new CallByValueReference().test();
}

private void test() {
    strArray.add(new myObject("entry1") );
    System.out.println(strArray);
    strArray.get(0).setStr("entry2");
    System.out.println(strArray);
}
}

The output is:

[myObject [str=entry1]]
[myObject [str=entry2]]