Question

I have a class,

class MyClass {
    private int val;
    public static final MyClass myObject = new MyClass(1);
    MyClass(int a){
        val = a;
    }
    public int getVal(){
        return val;
    }
    public MyClass func1(){
        MyClass temp = myObject;
        temp.val = 2;
        return temp;
    }
    public static void main(String [] args){
        MyClass x = new MyClass(4);
        System.out.println(myObject.getVal());
        x.func1();
        System.out.println(myObject.getVal());
    }
}

It prints:

 1
 2

I was expecting it to print:

 1 
 1

There seems to be a fundamental misunderstanding on my part. I was expecting that myObject being a final static value cannot be changed, and when I do MyClass temp = myObject, I create a new object called temp of type MyClass and assign the value of myObject to this newly created object. Please correct me if I am wrong. It seems that the there is no new object created and temp simply points to the original myObject

EDIT: Thanks for the answers! I now understand that the = operator never makes a copy of the object, it just copies the reference. What I need is to make a copy of myObject and store it in temp. What would be the best way to achieve this?

EDIT2: Another strange behavoir or a feature of Java?

I modified the code slightly

class MyClass {
    private Integer val;
    public static final MyClass myObject = new MyClass(1);
    MyClass(int a){
        val = a;
    }
    public int getVal(){
        return val;
    }
    public MyClass func1(){
        MyClass temp = new MyClass(33);
        temp.val = myObject.val;
        temp.val = 2;
        return temp;
    }
    public static void main(String [] args){
        MyClass x = new MyClass(4);
        System.out.println(myObject.getVal());
        MyClass y = x.func1();
        System.out.println(x.getVal());
        System.out.println(y.getVal());
        System.out.println(myObject.getVal());
    }
}

output is

 1
 4
 2
 1

Therefore, when I create temp using new MyClass(33) and then set temp.val = 2, it actually makes a copy of val. In other words, temp.val does not point to myObject.val. Why is this so?

Answer 1

MyClass temp = myObject;

That’s not creating a new instance, it’s just assigning the reference so that temp points to the same instance as myObject.

So your statement:

I create a new object called temp of
type MyClass

is incorrect, as you aren’t creating a new object here, just assigning an object reference.

EDIT
If your goal is to make a copy of myObject and return it from func1(), then you could do this (by copy I assume you mean copying the val value as well, if you want to use a different value for val then you can adjust this code accordingly):

public MyClass func1(){
    MyClass temp = new MyClass(myObject.getVal());
    return temp;
}