Question

I have the following code:

public class Test {

    public static void main(String[] args) {

        Integer alpha = new Integer(1);
        Integer foo = new Integer(1);

        if(alpha == foo) {
            System.out.println("1. true");
        }

        if(alpha.equals(foo)) {
            System.out.println("2. true");
        }

    } 

}

The output is as follows:

2. true

However changing the type of an Integer object to int will produce a different output, for example:

public class Test {

    public static void main(String[] args) {

        Integer alpha = new Integer(1);
        int foo = 1;

        if(alpha == foo) {
            System.out.println("1. true");
        }

        if(alpha.equals(foo)) {
            System.out.println("2. true");
        }

    } 

}

The new output:

1. true
2. true

How can this be so? Why doesn’t the first example code output 1. true?

Answer 1

For reference types, == checks whether the references are equal, i.e. whether they point to the same object.

For primitive types, == checks whether the values are equal.

java.lang.Integer is a reference type. int is a primitive type.

Edit: If one operand is of primitive type, and the other of a reference type that unboxes to a suitable primitive type, == will compare values, not references.