JAVA day15

 TreeSetDemo.java

public int compareTo(Object obj)     
{            
    if(!(obj instanceof Student))
        throw new RuntimeException("不是学生对象");   
     Student stu = (Student)obj;
            
    if((this.age == stu.age) && !this.name.equals(stu.name)) 
        return (this.name.compareTo(stu.name));
    else
        return (this.age-stu.age); 
}