基础深化和提高-java容器

package com.tong.map; import java.util.HashMap; import java.util.Map; import java.util.Set; public class HashMapTest { public static void main(String[] args) { //实例化HashMap容器 Map<String,String> map = new HashMap<>(); //添加元素 String put1 = map.put("a", "A"); String put2 = map.put("b", "B"); String put3 = map.put("c", "C"); String put4 = map.put("a", "AA"); System.out.println(put1+"\t"+put2+"\t"+put3+"\t"+put4); System.out.println("---------------"); //获取容器中元素的数量 int size = map.size(); System.out.println(size); System.out.println("-----------------"); //获取容器中的元素 //方式一 String v = map.get("a"); System.out.println(v); System.out.println("-------------"); //方式二 Set<String> keySet = map.keySet(); for(String key : keySet){ String value = map.get(key); System.out.println(key +" ------ "+ value); } System.out.println("--------------------"); //方式三 //Map.Entry就是一个键值对对象 Set<Map.Entry<String, String>> entrySet = map.entrySet(); //遍历Set获取每一个键值对 for(Map.Entry<String,String> entry:entrySet){ String key = entry.getKey(); String value = entry.getValue(); System.out.println(key+"-------------"+value); } System.out.println("------------------------"); //Map容器的并集操作 Map<String,String> map2 = new HashMap<>(); map2.put("f","F"); map2.put("c","CC"); map.putAll(map2); Set<String> keySet2 = map.keySet(); for(String key : keySet2){ String value = map.get(key); System.out.println(key +" ------ "+ value); } System.out.println("--------------------"); //删除元素 String a = map.remove("a"); System.out.println(a); System.out.println("--------------"); //判断Key是否存在 boolean b = map.containsKey("b"); System.out.println(b); System.out.println("-----------------"); //判断Value是否存在 boolean b1 = map.containsValue("B"); System.out.println(b1); } }