JAVA高级教程Java HashMap表达式(7)

7、HashMap的使用

students类

package Map01;import java.util.Objects ;public class Students implements Comparable<Students>{private String name;private  int stuNO;public Students() {}public Students(String age, int stuNO) {this.name = age;this.stuNO = stuNO;}public String getName() {return name;}public void setName(String age) {this.name = age;}public int getStuNO() {return stuNO;}public void setStuNO(int stuNO) {this.stuNO = stuNO;}@Overridepublic String toString() {return "Students{" +"age='" + name + '\'' +", stuNO=" + stuNO +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;Students students = (Students) o;return stuNO == students.stuNO && Objects.equals(name, students.name);}@Overridepublic int hashCode() {return Objects.hash(name, stuNO);}@Overridepublic int compareTo(Students o) {int n1=this.name.compareTo(o.getName());int n2=this.stuNO-o.getStuNO();return n2;}
}

package Map01;import Set01.Person;import java.util.HashMap;
import java.util.Map;public class Demo02_HashMap {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());}}
}