常用API

类别 方法
增加 put、putAll
删除 remove、removeAll、clear
查询 get
取值 entrySet、keySet、values
长度 size
判断 contains、containsAll、isEmpty

HashMap

键与值的关系（无序）

package com.jacob.javase.map;

import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

/*
 * HashMap:
 */
public class hashMapT {
    public static void main(String[] args) {
        Map h1 = new HashMap();
        h1.put(1, "c");
        h1.put(0, "b");
        h1.put(3, "a");

        // 键遍历：
        Set key = h1.keySet();
        iter(key);
        // 值遍历
        Collection value = h1.values();
        iter(value);
        // 键值遍历
        iter(key, h1);

        System.out.println(h1.size());
    }

    public static void iter(Set s) {
        Iterator i = s.iterator();
        while (i.hasNext()) {
            System.out.print(i.next() + " ");
        }
        System.out.println();
    }

    public static void iter(Collection s) {
        Iterator i = s.iterator();
        while (i.hasNext()) {
            System.out.print(i.next() + " ");
        }
        System.out.println();
    }

    public static void iter(Set s, Map h) {
        Iterator i = s.iterator();
        while (i.hasNext()) {
            Object temp = i.next();
            System.out.print(temp + ":" + h.get(temp) + " ");
        }
        System.out.println();
    }
}

TreeMap

有序

package com.jacob.javase.map;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

/*
 * treeMap：
 */
public class TreeMapT {
    public static void main(String[] args) {
        Map h1 = new TreeMap();
        h1.put(7, "c");
        h1.put(0, "b");
        h1.put(3, "a");
        h1.put(3, "d");

        Set s=h1.keySet();
        Iterator i = s.iterator();
        while (i.hasNext()) {
            Object temp=i.next();
            System.out.print(temp + ":"+h1.get(temp)+" ");
        }

    }
}

HashMap与Hashtable

类别 特点 （键/值）null值处理
HashMap 轻量级、线程不安全、处理慢 允许
HashTable 重量级、线程安全、处理慢 不允许