import java.util.HashMap;
import java.util.Map;
public class Demo01 {public static void main(String[] args) {show01();show02();show03();show04(); }private static void show04() {Map<String,Integer> map3 = new HashMap<>();map3.put("董",18);map3.put("皓",16);map3.put("宇",15);boolean m = map3.containsKey("皓");boolean m1= map3.containsKey("帅");System.out.println(m);//trueSystem.out.println(m1);//false}private static void show03() {Map<String,Integer> map2 = new HashMap<>();map2.put("董",18);map2.put("皓",16);map2.put("宇",15);Integer m = map2.get("皓");System.out.println(m);//16}private static void show02() {Map<String,Integer> map1 = new HashMap<>();map1.put("董",18);map1.put("皓",16);map1.put("宇",15);Integer m = map1.remove("宇");System.out.println(m);//15}private static void show01(){Map<String,String> map = new HashMap<>();String m1 = map.put("董","皓");String m2 = map.put("董","宇");System.out.println(m1);//nullSystem.out.println(m2);//返回的是被替换的值：皓System.out.println(map);//{董=宇}}
}

import java.util.HashMap;
import java.util.Map;
import java.util.Set;public class Demo02 {public static void main(String[] args) {Map<String,Integer> map = new HashMap<>();map.put("董",18);map.put("皓",16);map.put("宇",15);//1.先用keySet把Key值取出来，然后放在set集合中Set<String> set = map.keySet();//2.遍历set集合获取每一个keyfor (String name : set) {//3.用get()找到valueInteger value = map.get(name);System.out.println(name+"="+value);}System.out.println("======================");//用第二种方法来遍历,entrySet方法。Set<Map.Entry<String, Integer>> ent1 = map.entrySet();for (Map.Entry<String, Integer> entry : ent1) {String name = entry.getKey();Integer values = entry.getValue();System.out.println(name+"="+values);}}
}

import java.util.HashMap;
import java.util.Map;
import java.util.Set;public class Demo03 {public static void main(String[] args) {show01();}private static void show01(){HashMap<Person, String> map = new HashMap<>();map.put(new Person("董",18),"益阳");map.put(new Person("董",19),"株洲");map.put(new Person("董",20),"深圳");map.put(new Person("董",18),"地球");Set<Map.Entry<Person, String>> set = map.entrySet();for (Map.Entry<Person, String> entry : set) {Person key = entry.getKey();String value = entry.getValue();System.out.println(key+"="+value);//如果在person类里面添加了equals()和hashCode()方法后，会出现⬇️//Person{name='董', age=18}=地球//Person{name='董', age=19}=株洲//Person{name='董', age=20}=深圳}}
}

import java.util.HashMap;
import java.util.Scanner;public class Demo04 {public static void main(String[] args) {Scanner sc = new Scanner(System.in);System.out.println("请输入一个字符串");String str = sc.next();//1.创建一个HashMap的集合，Key是字符串的字符，Values是字符的个数HashMap<Character, Integer> map = new HashMap<>();//2.遍历字符串获取每一个字符for (char c : str.toCharArray()) {//3.判断key是否存在if(map.containsKey(c)){//存在的话Integer value = map.get(c);value++;map.put(c,value);}else{map.put(c,1);}}//4.遍历Map输出结果for (Character key : map.keySet()) {Integer value = map.get(key);System.out.println(key+"="+value);}}
}