6、Map的使用

package Map01;import java.util.HashMap;
import java.util.Map;
import java.util.Set;/*** Map接口的使用*/
public class Demo01_HashMap {public static void main(String[] args) {Map<String,String> map=new HashMap<>();map.put("cn","中国");map.put("uk","英国");map.put("usa","美国");map.put("usa","美国1");System.out.println("数据的个数"+map.size());System.out.println(map.toString());//删除map.remove("usa");//遍历//使用keysetSystem.out.println("============使用keyset======================");
//        Set<String> keys= map.keySet();for (String key : map.keySet()) {System.out.println(key+":"+map.get(key));}//使用entryset遍历System.out.println("============使用entryset遍历======================");
//        Set<Map.Entry<String,String>> entries=map.entrySet();for (Map.Entry<String, String> entry : map.entrySet()) {System.out.println(entry.getKey()+":"+entry.getValue());}}
}

public static void main(String[] args) {HashMap<Students,String> stu=new HashMap<>();Students p1=new Students("刘德华",20);Students p2=new Students("李小龙",22);Students p3=new Students("彭于晏",24);System.out.println("数据的个数"+stu.size());System.out.println(stu.toString());stu.put(p1,"上海");stu.put(p2,"北京");stu.put(p3,"深圳");//重写了hascode就不会重读stu.put(new Students("彭于晏",24),"深圳");System.out.println("数据的个数"+stu.size());System.out.println(stu.toString());//删除stu.remove(p1);//遍历//使用keysetSystem.out.println("============使用keyset======================");
//        Set<String> keys= map.keySet();for (Students key : stu.keySet()) {System.out.println(key+":"+stu.get(key));}//使用entryset遍历System.out.println("============使用entryset遍历======================");
//        Set<Map.Entry<String,String>> entries=map.entrySet();for (Map.Entry<Students, String> entry : stu.entrySet()) {System.out.println(entry.getKey()+":"+entry.getValue());}}