Learning Java

The Class Class

The last method of Object we need to discuss is getClass( ) . This method returns a reference to the Class object that produced the Object instance.

A good measure of the complexity of an object-oriented language is the degree of abstraction of its class structures. We know that every object in Java is an instance of a class, but what exactly is a class? In C++, objects are formulated by and instantiated from classes, but classes are really just artifacts of the compiler. Thus, you see classes only mentioned in C++ source code, not at runtime. By comparison, classes in Smalltalk are real, runtime entities in the language that are themselves described by “metaclasses” and “metaclass classes.” Java strikes a happy medium between these two languages with what is effectively a two-tiered system that uses Class objects.

Classes in Java source code are represented at runtime by instances of the java.lang.Class class. There’s a Class object for every class you use; this Class object is responsible for producing instances for its class. You don’t have to worry about any of this unless you are interested in loading new kinds of classes dynamically at runtime. The Class object is also the basis for “reflecting” on a class to find out its methods and other properties; we’ll discuss this feature in the next section.

We get the Class associated with a particular object with the getClass( ) method:

String myString = "Foo!" 
Class c = myString.getClass( );

We can also get the Class ...