THE PACKAGE JAVA.UTIL

java.util.Dictionary

21.4

21.4 The Class

java.util.Dictionary

A

Dictionary

 is an object that associates

elements

 with

keys

. Every key and

every element is an object. In any one

Dictionary

, every key is associated at

most one element. Given a

Dictionary

 and a key, the associated element can be

looked up.

public abstract class Dictionary {

abstract public int size();

abstract public boolean isEmpty();

abstract public Object get(Object key)

throws NullPointerException;

abstract public Object put(Object key, Object element)

throws NullPointerException;

abstract public Object remove(Object key)

throws NullPointerException;

abstract public Enumeration keys();

abstract public Enumeration elements();

}

As a rule, the

equals

 method ( 20.1.3) should be used by implementations of

the class

Dictionary

 to decide whether two keys are the same.

21.4.1

abstract public int size()

The general contract for the

size

 method is that it returns the number of entries

(distinct keys) in this dictionary.

21.4.2

abstract public boolean isEmpty()

The general contract for the

isEmpty

 method is that the result is

true

 if and only

if this dictionary contains no entries.

21.4.3

abstract public Object get(Object key)

throws NullPointerException

The general contract for the

isEmpty

 method is that if this dictionary contains an

entry for the specified

key

, the associated element is returned; otherwise,

null

 is

returned.

If the

key

 is

null

, a

NullPointerException

 is thrown.

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