Question

I have this:

import java.util.ArrayList;


public class MyClass {
    ArrayList list = new ArrayList();

    public MyClass(){

    }

    public MyClass(MyClass aClass){
        this.list = aClass.getList();
    }

    public void add(int number){
        list.add(number);
    }

    public void set(int number){
        list.set(0, number);
    }

    public int get(){
        return (Integer)list.get(0);
    }

    public ArrayList getList(){
        return list;
    }
}



MyClass aName = new MyClass();
aName.add(5);
System.out.println("aName: "+aName.get());

MyClass aName2 = new MyClass(aName);
System.out.println("aName2: "+aName2.get());

aName2.set(1);
System.out.println("aName2: "+aName2.get());
System.out.println("aName: "+aName.get());

This will print:
aName: 5
aName2: 5
aName2: 1
aName: 1

I don’t want my second object changing the values in my first object.
Is there any way to stop this happening but still be able to copy properties from another object?

Answer 1

Then don’t pass the List from the original object to the new object, in

public MyClass(MyClass aClass){ 
    this.list = aClass.getList(); 
} 

It makes both object have a reference to the same list (there is only one list shared between both objects).

You should do

public MyClass(MyClass aClass){ 
    this.list = (List) aClass.getList().clone(); 
}