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| Chapter 17 The java.util Package |

# Dictionary

## Name

Dictionary

## Synopsis

Class Name:

  `java.util.Dictionary`

Superclass:

  `java.lang.Object`

Immediate Subclasses:

  `java.util.Hashtable`

Interfaces Implemented:

  None

Availability:

  JDK 1.0 or later

## Description

The `Dictionary` class is an `abstract` class that associates keys with values. Any non-`null` object can be used as a key or as a value. Key/value pairs can be stored in a `Dictionary`, and values can be retrieved or removed using their associated keys.

A subclass of `Dictionary` should use the `equals()` method to decide if two keys are equivalent.

## Class Summary

    public abstract class java.util.Dictionary extends java.lang.Object {
      // Instance Methods
      public abstract Enumeration elements();
      public abstract Object get(Object key);
      public abstract boolean isEmpty();
      public abstract Enumeration keys();
      public abstract Object put(Object key, Object value);
      public abstract Object remove(Object key);
      public abstract int size();
    }

## Instance Methods

### elements

#### public abstract Enumeration elements()

Returns

  The values in the dictionary as an `Enumeration`.

Description

  This method returns an `Enumeration` that iterates through the values in this `Dictionary`.

### get

#### public abstract Object get(Object key)

Parameters

  `key`

    The key of the value to retrieve.

Returns

  The value that corresponds to this key.

Description

  This method returns the value that is associated with the given key.

### isEmpty

#### public abstract boolean isEmpty()

Returns

  `true` if there are no values in the `Dictionary`7thinsp;; `false` otherwise.

Description

  This method returns a `boolean` value that indicates whether or not the `Dictionary` is empty.

### keys

#### public abstract Enumeration keys()

Returns

  The keys in the dictionary as an `Enumeration`.

Description

  This method returns an `Enumeration` that iterates through the keys in this `Dictionary`.

### put

#### public abstract Object put(Object key, Object value)

Parameters

  `key`

    A key object.

  `value`

    A value object.

Returns

  The previous value associated with the given key or `null` if `key` has not previously been associated with a value.

Throws

  `NullPointerException`

    If either the key or the value is `null`.

Description

  This method associates the given key with the given value in this `Dictionary`.

### remove

#### public abstract Object remove(Object key)

Parameters

  `key`

    The key of the value to remove.

Returns

  The value associated with the given key or `null` if `key` is not associated with a value.

Description

  This method removes a key/value pair from this `Dictionary`. If the given key is not in the `Dictionary`, the method does nothing.

### size

#### public abstract int size()

Returns

  The number of keys in the `Dictionary`.

Description

  This method returns the number of key/value pairs in this `Dictionary`.

## Inherited Methods

Method | Inherited From | Method | Inherited From
--- | --- | --- | ---
`clone()` | `Object` | `equals(Object)` | `Object`
`finalize()` | `Object` | `getClass()` | `Object`
`hashCode()` | `Object` | `notify()` | `Object`
`notifyAll()` | `Object` | `toString()` | `Object`
`wait()` | `Object` | `wait(long)` | `Object`
`wait(long, int)` | `Object` |  |

## See Also

`Enumeration`, `Hashtable`, `NullPointerException`

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