Java之HashMap用法

源码：

package test_demo;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Random;

/*
 * @desc HashMap测试程序
 */

public class HashMapDemo {
    private static void testHashMapAPIs() {
        // 初始化随机种子
        Random r = new Random();
        // 新建HashMap
        HashMap map = new HashMap();
        // 添加操作
        map.put("one", r.nextInt(10));
        map.put("two", r.nextInt(10));
        map.put("three", r.nextInt(10));
        // 打印出map
        System.out.println("map:" + map);
        // 通过Iterator遍历key-value
        Iterator iter = map.entrySet().iterator();
        while (iter.hasNext()) {
            Map.Entry entry = (Map.Entry) iter.next();
            System.out.println("next :  " + entry.getKey() + ":" + entry.getValue());
        }
        // HashMap的键值对个数
        System.out.println("size:" + map.size());
        // containsKey(Object key) :是否包含键key
        System.out.println("contains key two : " + map.containsKey("two"));
        System.out.println("contains key five : " + map.containsKey("five"));
        // containsValue(Object value) :是否包含值value
        System.out.println("contains value 0 : " + map.containsValue(new Integer(0)));
        // remove(Object key) ： 删除键key对应的键值对
        map.remove("three");
        System.out.println("删除three");
        System.out.println("map:" + map);
        // clear() ： 清空HashMap
        map.clear();
        System.out.println("清空HashMap");
        // isEmpty() : HashMap是否为空
        System.out.println((map.isEmpty() ? "map is empty" : "map is not empty"));
    }

    public static void main(String[] args) {
        testHashMapAPIs();
    }
}

执行结果：

map:{one=1, two=9, three=2}
next :  one:1
next :  two:9
next :  three:2
size:3
contains key two : true
contains key five : false
contains value 0 : false
删除three
map:{one=1, two=9}
清空HashMap
map is empty