基础视频day15练习1 - 黑马程序员技术交流社区

package fuxi1;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
/**
* 题目：每一个学生都有对应的归属地，学生Student，归属地String，学生有属性姓名和年龄，属性相同视为同一个学生。保证学生的唯一性。
* 思路：1.先描述学生，因为要确保唯一性，所以要用HashMap集合，学生类中要覆盖hashCode()和equals（）方法。
* 2.定义Map集合，将学生和归属地作为键值存入
* 3.获取集合中的元素
*@author XiaLei
*/
public class Day16Test4 {
public static void main(String[] args) {
Students st1 = new Students("java01",5);
Students st2 = new Students("java02",2);
Students st3 = new Students("java04",4);
Students st4 = new Students("java01",5);
String addr1 = st1.diZhi("BeiJin01");
String addr2 = st1.diZhi("BeiJin02");
String addr3 = st1.diZhi("BeiJin03");
String addr4 = st1.diZhi("BeiJin04");
Map<Students,String> m = new HashMap<Students,String>();
m.put(st1,addr1);
m.put(st2,addr2);
m.put(st3,addr3);
m.put(st4,addr4);
//entrySet取出方式：
Set<Map.Entry<Students,String>> s = m.entrySet();
Iterator<Map.Entry<Students,String>> it = s.iterator();
while(it.hasNext()){
Map.Entry<Students, String> me = it.next();
Students key = me.getKey();
String value = me.getValue();
System.out.println(key+"="+value);
}
//keySet取出方式：
Set<Students> st = m.keySet();
for(Iterator<Students> its =st.iterator();its.hasNext();){
Students key1 = its.next();
String value1 = m.get(key1);
System.out.println(key1+"="+value1);
}
}
}
class Students implements Comparable<Students>{//实现Comparable接口，让Students类具有自然顺序。
private String name;
private int age;
public Students(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String diZhi(String addr){
return addr;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
public int compareTo(Students s){
int num = this.age-s.age;
if(num==0){
return this.name.compareTo(s.name);
}
return num;
}
public int hashCode(){
return name.hashCode()+age*39;
}
public boolean equals(Object obj){
if (!(obj instanceof Students))
throw new RuntimeException("类型不匹配");//注意异常的使用，这里如果return false；没有意义所以要抛出一个运行时异常。
Students st = (Students)obj;
return this.name.equals(st.name) && this.age==st.age;
}
public String toString(){
return "name:"+name+"...age:"+age;
}
}

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