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  • Java基础系列

    package com.test3;
    
    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map.Entry;
    
    public class demo3 {
    
        public static void main(String[] args) {
            HashMap<String, String> map = new HashMap<>();
            map.put("zhang", "31");//存放键值对
    
            System.out.println(map.containsKey("zhang"));//键中是否包含这个数据
            System.out.println(map.containsKey("daniu"));
            System.out.println("=========================");
    
            System.out.println(map.get("zhang"));//通过键拿值
            System.out.println(map.get("daniu"));
            System.out.println("=========================");
    
            System.out.println(map.isEmpty());//判空
            System.out.println(map.size());
            System.out.println("=========================");
    
            System.out.println(map.remove("zhang"));//从键值中删除
            System.out.println(map.containsKey("zhang"));
            System.out.println(map.get("zhang"));//获取值
            System.out.println(map.isEmpty());
            System.out.println(map.size());
            System.out.println("=========================");
    
            map.put("zhang", "31");
            System.out.println(map.get("zhang"));
            map.put("zhang", "32");
            System.out.println(map.get("zhang"));
            System.out.println("=========================");
    
            map.put("zhang", "31");
            map.put("cheng", "32");
            map.put("yun", "33");
    
            for (String key : map.keySet()) {
                System.out.println(key);
            }
            System.out.println("=========================");
    
            for (String values : map.values()) {
                System.out.println(values);
            }
            System.out.println("=========================");
    
            map.clear();
            map.put("A", "1");
            map.put("B", "2");
            map.put("C", "3");
            map.put("D", "1");
            map.put("E", "2");
            map.put("F", "3");
            map.put("G", "1");
            map.put("H", "2");
            map.put("I", "3");
            for (Entry<String, String> entry : map.entrySet()) {
                String key = entry.getKey();
                String value = entry.getValue();
                System.out.println(key + "," + value);
            }
            System.out.println("=========================");
    
            // you can not remove item in map when you use the iterator of map
            // for(Entry<String,String> entry : map.entrySet()){
            // if(!entry.getValue().equals("1")){
            // map.remove(entry.getKey());
            // }
            // }
    
            // if you want to remove items, collect them first, then remove them by
            // this way.
            List<String> removeKeys = new ArrayList<String>();
    
            for (String removeKey : removeKeys) {
                map.remove(removeKey);
            }
            for (Entry<String, String> entry : map.entrySet()) {
                String key = entry.getKey();
                String value = entry.getValue();
                System.out.println(key + "," + value);
            }
            System.out.println("=========================");
    
        }
    }
    

      

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  • 原文地址:https://www.cnblogs.com/smartsmile/p/11541640.html
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