Java passing by value and autoboxing

Java is pass by value

Some important things to keep in my when passing around objects in Java.  Java is pass by value which really means "pass by a copy of something".  However this confuses people because you're not passing a copy of an object in java, you're passing a copy of a pointer to an object. This example helps clairfy.

    private void runMe() {
        Dog aDog = new Dog("Max");
        foo(aDog);

        if (aDog.getName().equals("Max")) { //true
            System.out.println( "Java passes by value." );

        } else if (aDog.getName().equals("Fifi")) {
            System.out.println( "Java passes by reference." );
        }
    }

    public void foo(Dog d) {
        d.getName().equals("Max"); // true

        d = new Dog("Fifi");
        d.getName().equals("Fifi"); // true
    }

Output...

Java passes by value.

But watch out for autoboxing

This isn't quite the same for autoboxed primitive types (Integer, Float, Double), or apparantly anything assigned a value directly with the equals sign.  You would think that given it's appearance Integer would function like the Dog class above.  However, this appears to be assigning the reference value a new instance.  Just something to watch out for.  See this for more information.

    private void runMe() {

        Something test0 = new Something("asdf");
        updateTest(test0);
        System.out.println("test1 is: " + test0.value);

        String test1 = "asdf";
        updateTest(test1);
        System.out.println("test1 is: " + test1);

        Boolean test2 = false;
        updateTest(test2);
        System.out.println("test2 is: " + test2);

        Character test3 = 'a';
        updateTest(test3);
        System.out.println("test3 is: " + test3);
    }

    private void updateTest(Something test0) {
        test0.value = "qwer";
    }

    private void updateTest(Character test3) {
        test3 = 'b';
    }

    private void updateTest(String test1) {
        test1 = "qwer";
    }

    private void updateTest(Boolean test) {
        test = true;
    }

Output...

test1 is: qwer
test1 is: asdf
test2 is: false
test3 is: a 

And just to be clear that goes for primitives too

Java is pass by value, which mean pass by a copy of something.  Primitives will not be updated if reassigned in a method.

private void runMe() {
        int a = 123;

        udpateIt(a);

System.out.println(a); } private void updateIt(int value) 

Output...

123