java Hashmap

HashMap的基本功能

public static void main(String[] args) {
        Map map=new HashMap();
        map.put("za","zz");
        map.put("aaa","gg");
        map.put("xx","yy");
        /*System.out.println(map);
        System.out.println(map.remove("za"));
        System.out.println(map.containsKey("aaa"));
        System.out.println( map.containsValue("gg"));*/
        /*System.out.println(map.get("aaa"));//根据建获取值
        Set keySet = map.keySet();//获取所有建的集合
        for(String key:keySet)
        {
            System.out.println(key);
        }
        Collection values = map.values();//获取所有值的集合
        for(String value:values)
        {
            System.out.println(value);
        }*/
        /*Set keySet = map.keySet();
        for(String key:keySet)
        {
            String value = map.get(key);
            System.out.println(key+","+value);
        }*/
        Set> entrySet = map.entrySet();
        for(Map.Entry me:entrySet)
        {
            String key=me.getKey();
            String value=me.getValue();
            System.out.println(key+","+value);
        }

    }

HashMap集合

键是String 值是Student

HashMaphm=new HashMap();
        Student s1=new Student("aa",30);
        Student s2=new Student("bbba",20);
        hm.put("itheima01",s1);
        hm.put("itheima02",s2);
        Set keySet = hm.keySet();
        for(String key:keySet)
        {
            Student value=hm.get(key);
            System.out.println(key+","+value.getName()+","+value.getAge());
        }
        Set> entrySet = hm.entrySet();
        for(Map.Entry me:entrySet)
        {
            String key = me.getKey();
            Student value = me.getValue();
            System.out.println(key+","+value.getName()+","+value.getAge());
        }

键是Student 值是String

HashMap hm=new HashMap();
        Student s1=new Student("aa",20);
        Student s2=new Student("bb",30);
        Student s3=new Student("bb",30);
        hm.put(s1,"xian");
        hm.put(s2,"wuhan");
        hm.put(s3,"beijing");
        Set keySet = hm.keySet();
        for(Student key:keySet)
        {
            String value=hm.get(key);
            System.out.println(key.getName()+","+key.getAge()+","+value);
        }