HashMap

public class HashMapTest1 {
    public static void main(String[] args) {
        //创建对象
        //年龄,名字相同认为是同一个人(要重写hashCode和equals方法)
        HashMap<Student,String> hm=new HashMap<>();
        Student s1=new Student("zhangsan",23);
        Student s2=new Student("lisi",24);
        Student s3=new Student("wangwu",25);
        Student s4=new Student("wangwu",25);
        hm.put(s1,"北京");
        hm.put(s2,"上海");
        hm.put(s3,"广州");
        hm.put(s4,"深圳");
        //键值对
        Set<Map.Entry<Student, String>> set = hm.entrySet();
        for(Map.Entry<Student, String> entry:set){
            System.out.println(entry.getKey()+"--"+entry.getValue());
        }
        System.out.println("------------------");
        //lambda
        hm.forEach((key, Value)-> System.out.println(key+"--"+Value));
        System.out.println("------------------");
        //键找值
        Set<Student> set1 = hm.keySet();
        Iterator<Student> it=set1.iterator();
        while(it.hasNext()){
            Student key = it.next();
            System.out.println(key+"--"+hm.get(key));
        }
    }
}
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public class HashMapTest2 {
    public static void main(String[] args) {
        /*
        练习:八十个学生给四个景点投票,统计每个景点的得票情况
         */
        //如果要统计的东西较多,可以使用计数器思想

        //创建一个数组来存放投票的对象
        String []arr={"A","B","C","D"};
        //创建一个集合来存放投票结果
        ArrayList<String> list=new ArrayList<>();
        Random r=new Random();
        for(int i=0;i<80;i++){
            int index = r.nextInt(arr.length);
            list.add(arr[index]);
        }
        //创建hashmap集合来存放每个元素的个数
        HashMap<String,Integer> map=new HashMap<>();
        //遍历list集合来统计票数
        for (String s : list) {
            if(!map.containsKey(s)){
                map.put(s,1);
            }else{
                int count=map.get(s);
                count++;
                map.put(s,count);
            }
        }
        //打印结果
        map.forEach((key,value)-> System.out.println(key+"景点的票数为:"+value));
        //求最大值
        int max=0;
        Set<String> set1 = map.keySet();
        for (String s : set1) {
            if(map.get(s)>max){
                max=map.get(s);
            }
        }
        System.out.println("最大值为:"+max);
        //得到最大值的景点
        for (String s : set1) {
            int count=map.get(s);
            if(count==max){
                System.out.println(s+"景点的票数为:"+count);
            }
        }
        //上方两步不能合在一起
    }
}
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public class LinkedHashMapDemo1 {
    public static void main(String[] args) {
        //有序,不重复,无索引
        //底层是哈希表+双向链表
        //1.创建集合
        LinkedHashMap<String,Integer> lhp=new LinkedHashMap<>();
        //2.添加元素
        lhp.put("xiangxiang",1);
        lhp.put("haha",2);
        lhp.put("baby",3);
        lhp.put("baby",4);
        //打印结果
        System.out.println(lhp);//{xiangxiang=1, haha=2, baby=4}
    }
}