Although, for (almost) all intents and purposes we can treat it as a button! 

Other details like its properties and any associated methods.

What is an object reference?

Apart from primitives , all Java objects are actually references. A primitive, such as an int , boolean or double, is stored directly into a memory location:

When you instantiate an object such as a button:

b is not actually a Button object , strictly speaking it's a reference to a button instance (it specifies where in memory the Button and it's associated methods are to be found).

Assume we create a second button object:

Somewhere in physical computer memory these details are stored:

 If we make an assignment such as:

 We overwrite the reference ( Button c now references the same address that b references ("Press me"). The memory occupied by "Press me not" is no longer referenced and becomes inaccessible storage.

Any methods available to c, such as setColor(blue), will now affect button b ("Press me"), that is:

   b.setColor(Color.BLUE);
    c.setColor(Color.BLUE);

will now affect the same object instance.

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A class defines an Object; when the constructor of the class is called (with the new keyword) a new instance of that object is created.

Often we use the words object and instance interchangeably.

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