Dictionary抽象类

package java.util;

//抽象类，所有key-value键值对(HashTable)的父类，
public abstract
class Dictionary<K,V> {

    public Dictionary() {
    }
    abstract public int size();  //键值对size
    abstract public boolean isEmpty(); //判断是否空
    abstract public Enumeration<K> keys(); //key构成枚举类
    abstract public Enumeration<V> elements(); //value构成枚举类
    abstract public V get(Object key); //由key获取value
    abstract public V put(K key, V value);//将key-value放入到字典中
    abstract public V remove(Object key);//移除一个键值对
}