17.重写equals()

//学生类
public class Student {
    //属性
    private int sid;//学员学号
    private String name;//姓名
    private int age;//年龄
    private double weight;//体重
    
    //无参构造方法
    public Student() {
        //使用无参构造方法构造学员时，为其属性赋值
        this.name="无名氏";
        this.age=18;
        this.weight=50;
    }

    //构造方法重载 ：带参构造方法
    public Student(int sid,String name, int age, double weight) {
        this.sid=sid;
        this.name = name;
        this.weight = weight;
        if(age<18 || age>30){
            System.out.println("***输入的年龄为："+age+"，该年龄不合法，将重置!***");
            this.age=18;
        }else{
            this.age = age;
        }
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        if(age<18 || age>30){
            System.out.println("***输入的年龄为："+age+"，该年龄不合法，将重置!***");
            return;

        }
        this.age = age;
    }

    public double getWeight() {
        return weight;
    }

    public void setWeight(double weight) {
        this.weight = weight;
    }

    public int getSid() {
        return sid;
    }

    public void setSid(int sid) {
        this.sid = sid;
    }

    //重写equals()方法，如果学员学号、姓名都相同，证明是同一个学生
    //instanceof操作符用于判断一个引用类型所引用的对象是否是一个类的实例
    public boolean equals(Object o){
        if(this==o){
            return true;
        }
        if(! (o instanceof Student)){
            return false;
        }
        Student obj=(Student)o;
        if(this.sid==obj.sid && this.name.equals(obj.name)){
            return true;
        }else{
            return false;
        }        
    }
    
    public static void main(String[] args) {
        //Student没有重写equals()时,下列两行代码结果：false；重写后，结果：true
        Student s1=new Student(1,"张三",20,55);
        Student s2=new Student(1,"张三",20,55);
        System.out.println(s1.equals(s2));
        //思考：字符串的比较
    }
}