Map

public class MapDemo1 {
    public static void main(String[] args) {
        /*
        V put(K key, V value)//添加元素
        V remove(Object key)//根据键删除键值对元素
        void clear()//移除所有的键值对元素
        boolean containsKey(Object key)//判断集合是否包含指定的键
        boolean containsValue(Object value)//判断集合是否包含指定的值
        boolean isEmpty()//判断集合是否为空
        int size()//集合的长度，也就是集合中键值对的个数
         */
        //创建集合对象
        Map<String,String> map=new HashMap<>();
        //1.添加元素
        //put方法的细节:
        //添加/覆盖
        //添加数据时如果键不存在,则直接添加键值对,并返回null
        //添加数据时如果键存在,则覆盖原来的键值对,并返回原来的值
        String value1=map.put("zhangsan","1");
        map.put("lisi","2");
        map.put("wangwu","3");
        String value2=map.put("zhangsan","4");
        System.out.println(value1);//null
        System.out.println(value2);//1
        System.out.println(map);//{lisi=2, zhangsan=4, wangwu=3}

        //2.删除元素
        String s1=map.remove("zhangsan");
        System.out.println(s1);//4
        System.out.println(map);//{lisi=2, wangwu=3}
        //3.清空
        //map.clear();
        //4,5.判断是否包含
        boolean keyResult=map.containsKey("lisi");
        boolean valueResult=map.containsValue("3");
        System.out.println(keyResult);//true
        System.out.println(valueResult);//true

        //6.判空
        boolean flag=map.isEmpty();
        System.out.println(flag);//false

        //7.长度
        int size=map.size();
        System.out.println(size);//2
    }
}
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public class MapDemo2 {
    public static void main(String[] args) {
        //遍历
        Map<String,String> map=new HashMap<>();
        map.put("zhangsan","1");
        map.put("lisi","2");
        map.put("wangwu","3");
        //1.键找值
        //获取所有的键,并且放到一个单列集合中,再用get方法获得值
        Set<String> set = map.keySet();
        for (String s : set) {
            System.out.println(s+"="+map.get(s));
        }
        System.out.println("-------------");
        Iterator<String> it = set.iterator();
        while(it.hasNext()){
            String key = it.next();
            System.out.println(key+"="+map.get(key));
        }
        System.out.println("-------------");
        set.forEach(key-> System.out.println(key+"="+map.get(key)));
        System.out.println("-------------");
        //2.键值对
        //通过方法获取所有的键值对,并且返回一个set集合
        Set<Map.Entry<String, String>> set1 = map.entrySet();
        for(Map.Entry<String, String> entry:set1){
            String key = entry.getKey();
            String value = entry.getValue();
            System.out.println(key+"="+value);
        }
        System.out.println("-------------");
        Iterator<Map.Entry<String, String>> it2 = set1.iterator();
        while(it2.hasNext()){
            Map.Entry<String, String> entry = it2.next();
            String key = entry.getKey();
            String value = entry.getValue();
            System.out.println(key+"="+value);
        }
        System.out.println("-------------");
        set1.forEach(entry-> System.out.println(entry.getKey()+"="+entry.getValue()));
        System.out.println("-------------");
        //3.lambda表达式
        map.forEach(new BiConsumer<String, String>() {
            @Override
            public void accept(String key, String value) {
                System.out.println(key+"="+value);
            }
        });
        System.out.println("-------------");
        //简化
        map.forEach((key,value)-> System.out.println(key+"="+value));
    }
}