java容器 抽象类Dictionary源码分析

简介

/**
 * Dictionary类是Hashtable，它将键映射到值。
 * 每个键和值都是一个对象。在任何一个Dictionary对象中，每个键最多与一个值关联。
 * 给定一个字典和一个键，就可以查找相关的元素。任何非空对象都可以用作键和值。
 * 
 * 

 * 作为一个规则，这个类的实现应该使用equals方法来确定两个键是否相同。
 * 

 * 注意:这个类已经过时了。新的实现应该实现Map接口，而不是扩展这个类。
 *
 * @author  unascribed
 * @see     java.util.Map
 * @see     java.lang.Object#equals(java.lang.Object)
 * @see     java.lang.Object#hashCode()
 * @see     java.util.Hashtable
 * @since   JDK1.0
 */
public abstract
class Dictionary 

构造器函数，size,isEmpty,keys,elements

    /**
     * Sole constructor.  (For invocation by subclass constructors, typically
     * implicit.)
     */
    public Dictionary() {
    }

    /**
     * Returns the number of entries (distinct keys) in this dictionary.
     *
     * @return  the number of keys in this dictionary.
     */
    abstract public int size();

    /**
     * Tests if this dictionary maps no keys to value. The general contract
     * for the isEmpty method is that the result is true if and only
     * if this dictionary contains no entries.
     *
     * @return  true if this dictionary maps no keys to values;
     *          false otherwise.
     */
    abstract public boolean isEmpty();

    /**
     * 返回此字典中键的enumeration。
     * keys方法的一般约定是返回一个Enumeration对象，该对象将生成字典中包含的所有键。
     *
     * @return  an enumeration of the keys in this dictionary.
     * @see     java.util.Dictionary#elements()
     * @see     java.util.Enumeration
     */
    abstract public Enumeration keys();

    /**
     * 返回此字典中values的enumeration。
     * elements方法的一般约定是返回一个Enumeration对象，该对象将生成字典中包含的所有value。
     *
     * @return  an enumeration of the values in this dictionary.
     * @see     java.util.Dictionary#keys()
     * @see     java.util.Enumeration
     */
    abstract public Enumeration elements();

get,put,remove

    /**
     * Returns the value to which the key is mapped in this dictionary.
     * The general contract for the isEmpty method is that if this
     * dictionary contains an entry for the specified key, the associated
     * value is returned; otherwise, null is returned.
     *
     * @return  the value to which the key is mapped in this dictionary;
     * @param   key   a key in this dictionary.
     *          null if the key is not mapped to any value in
     *          this dictionary.
     * @exception NullPointerException if the key is null.
     * @see     java.util.Dictionary#put(java.lang.Object, java.lang.Object)
     */
    abstract public V get(Object key);

    /**
     * Maps the specified key to the specified
     * value in this dictionary. Neither the key nor the
     * value can be null.
     * 

     * If this dictionary already contains an entry for the specified
     * key, the value already in this dictionary for that
     * key is returned, after modifying the entry to contain the
     *  new element. 
If this dictionary does not already have an entry
     *  for the specified key, an entry is created for the
     *  specified key and value, and null is
     *  returned.
     * 

     * The value can be retrieved by calling the
     * get method with a key that is equal to
     * the original key.
     *
     * @param      key     the hashtable key.
     * @param      value   the value.
     * @return     the previous value to which the key was mapped
     *             in this dictionary, or null if the key did not
     *             have a previous mapping.
     * @exception  NullPointerException  if the key or
     *               value is null.
     * @see        java.lang.Object#equals(java.lang.Object)
     * @see        java.util.Dictionary#get(java.lang.Object)
     */
    abstract public V put(K key, V value);

    /**
     * Removes the key (and its corresponding
     * value) from this dictionary. This method does nothing
     * if the key is not in this dictionary.
     *
     * @param   key   the key that needs to be removed.
     * @return  the value to which the key had been mapped in this
     *          dictionary, or null if the key did not have a
     *          mapping.
     * @exception NullPointerException if key is null.
     */
    abstract public V remove(Object key);