Java in a Nutshell, 5th Edition

Name

Object

Synopsis

This is the root class in Java. All classes are subclasses of Object, and thus all objects can invoke the public and protected methods of this class. For classes that implement the Cloneable interface, clone( ) makes a byte-for-byte copy of an Object. getClass( ) returns the Class object associated with any Object, and the notify( ) , notifyAll( ), and wait( ) methods are used for thread synchronization on a given Object.

A number of these Object methods should be overridden by subclasses of Object. For example, a subclass should provide its own definition of the toString( ) method so that it can be used with the string concatenation operator and with the PrintWriter.println( ) methods. Defining the toString( ) method for all objects also helps with debugging.

The default implementation of the equals( ) method simply uses the = = operator to test whether this object reference and the specified object reference refer to the same object. Many subclasses override this method to compare the individual fields of two distinct objects (i.e., they override the method to test for the equivalence of distinct objects rather than the equality of object references). Some classes, particularly those that override equals( ), may also want to override the hashCode( ) method to provide an appropriate hashcode to be used when storing instances in a Hashtable data structure.

A class that allocates system resources other than memory (such as file descriptors or windowing system ...