java接口——map

 

一般使用HashMap

import java.util.*;

/**
 * 测试Map的使用方式
 */
public class MapTest {
    public static void main(String[] args) {
        Test02();
        iterateListSet();
        Test03();
    }
    //Map的常见用法
    public static void Test01(){
        Map m1 = new HashMap();//HashMap()替换
        m1.put(1,"one");
        m1.put(2,"two");
        m1.put(3,"three");
        System.out.println(m1);

        m1.put(2,"二");//如果键重复，(equals()为核心进行判断)，则会替换掉旧的键值对。
        Object obj = m1.get(2);
        System.out.println(obj);
        System.out.println(m1);
        System.out.println(m1.size());
        System.out.println(m1.isEmpty());
        System.out.println(m1.containsKey(4));//包含键3吗
        System.out.println(m1.containsValue("three"));//包含值three吗
        m1.remove(3);//从容器中移除键值对
        System.out.println(m1);

        Map m2 = new HashMap();
        m2.put("yi","1111");
        m2.put("er","2222");
        m2.put(3,"3333");
        m1.putAll(m2);
        System.out.println(m1);

    }

    //泛型的简单应用
    public static void Test02(){
        List<String> list = new ArrayList();//泛型描述为String,存取、返回等操作就直接时String,不用强制转型。
        list.add("aaa");
        String str = list.get(0);
        System.out.println(str);

        Set<Integer> set = new HashSet();
        set.add(1);

        Map<String,String> map = new HashMap();
        map.put("一","one");
        map.put("二","two");
        
    }

    //遍历set、list
    public static void iterateListSet(){
        List<String> list = new ArrayList();
        list.add("aaa");
        list.add("bbb");
        list.add("ccc");

        //通过索引遍历list,只适合于List
        for(int i=0;i<list.size();i++) {
             String temp = list.get(i);
            System.out.println(temp);
        }
        //通过增强for循环，可以用于Set
        for(String temp:list) {
            System.out.println(temp);
        }

        //使用Iterator对象,可以用于Set
        for (Iterator<String> iter = list.iterator()/*初始化变量*/;iter.hasNext();/*判断有没有下一个*/) {
            String temp = iter.next();//把当前正在遍历的对象返回，同时指向下一个。
            System.out.println(temp);

        }
    }

    //遍历Map(遍历key或者value)
    public static void Test03(){
        Map<String,String> map = new HashMap();
        map.put("one","一");
        map.put("two","二");
        map.put("three","三");

        //遍历键
        Set<String> keys = map.keySet();
        for(String temp:keys){
           // System.out.println(temp);
            System.out.println(temp+"----"+map.get(temp));
        }

        //遍历值
        Collection<String> values = map.values();
        for(String temp:values){
            System.out.println(temp);
        }

        //使用EntrySet遍历key和value.
        Set<Map.Entry<String,String>> entrySet = map.entrySet();
        for(Map.Entry e:entrySet){
            System.out.println(e.getKey()+"==="+e.getValue());

        }

    }



}