Map也是存储数据的集合类,在java.util中;其采取键值对的方式:key,value,其中key是唯一;
较List的key为int类型,但Map的key不局限int类型;
key只允许一个null,如果有第二个时就覆盖第一个;value可以多个null;
map.put(null,"Star");
map.put(null,"Janny");
map.put("name05",null);
map.put("name06",null);
分类:HashMap,HashTable,LinkedHashMap,TreeMap;
1、 关于HashMap方法:
import java.util.*;
public class Map{
public static void main(String []args){
HashMap<String,String> map=new HashMap<String,String>();
HashMap<String,String> map2=new HashMap<String,String>();
map.put("name01","Allen");
map.put("name02","Jack");
map.put("name03","Luu");
map.put("name04","Jone");
map.put(null,"Star");
map.put(null,"Janny");
map.put("name05",null);
map.put("name06",null);
map2.putAll(map);
System.out.println(map.get("name01"));
System.out.println(map.get("name02"));
System.out.println(map.get("name03"));
System.out.println(map.get(null));
map.remove("name01");
map.clear();
System.out.println(map);
System.out.println(map2);
System.out.println(map.isEmpty());
System.out.println(map.size());
}
}
2、方法: