import java.util.*;
class Student{String id;String name;public Student(String id,String name) {this.id=id;this.name=name;}public String toString() {return id+":"+name;}//重写hashCode()方法public int hashCode() {return id.hashCode() ;//返回id属性的哈希值}//重写equals()方法public boolean equals(Object obj) {if(this==obj) {return true;//判断是否为同一个对象}if(!(obj instanceof Student)) {//判断对象是否为Student类型return false;}Student stu=(Student)obj;boolean b=this.id.equals(stu.id);return b;}
}
public class Example {
public static void main(String[]args) {HashSet hset=new HashSet();hset.add(new Student("1","张三"));hset.add(new Student("2","李四"));hset.add(new Student("2","李四"));System.out.println(hset);
}
}

运行结果：

[1:张三, 2:李四]