20.1

java.lang.Object

THE PACKAGE JAVA.LANG

integer. The integer may be positive, negative, or zero. This integer does not,

however, have to remain consistent from one Java application to another, or

from one execution of an application to another execution of the same appli 

cation.

If two objects are equal according to the

equals

 method ( 20.1.3), then call 

ing the

hashCode

 method on each of the two objects must produce the same

integer result.

It is

not

 required that if two objects are unequal according to the

equals

method ( 20.1.3), then calling the

hashCode

 method on each of the two

objects must produce distinct integer results. However, the programmer

should be aware that producing distinct integer results for unequal objects

may improve the performance of hashtables.

As much as is reasonably practical, the

hashCode

 method defined by class

Object

 does return distinct integers for distinct objects. (This is typically imple 

mented by converting the internal address of the object into an integer, but this

implementation technique is not required by the Java language.)

Overridden by

Boolean

 ( 20.4),

Character

 ( 20.5),

Integer

 ( 20.7),

Long

( 20.8),

Float

 ( 20.9),

Double

 ( 20.10),

String

 ( 20.12), and

Bitset

 ( 21.2).

20.1.5

protected Object clone()

throws CloneNotSupportedException

The general contract of clone is that it creates and returns a copy of this object.

The precise meaning of  copy  may depend on the class of the object. The general

intent is that, for any object

x

, the expression:

x.clone() != x

will be

true

, and that the expression:

x.clone.getClass() == x.getClass()

will be

true

, but these are not absolute requirements. While it is typically the case

that:

x.clone.equals(x)

will be

true

, this is not an absolute requirement. Copying an object will typically

entail creating a new instance of its class, but it also may require copying of inter 

nal data structures as well.

The method

clone

 for class

Object

 performs a specific cloning operation.

First, if the class of this object does not implement the interface

Cloneable

, then

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