java继承中关于覆盖方法和子类构造器

覆盖方法
1.在父类中一些方法并不适合子类所以用新的方法来覆盖.
本文用People类和Student类进行解释
定义父类People

public class People {
    private  String name;
    private  String sex;
    private int age;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public void  run(){
        System.out.println("sass run");
    }
    public People(String name, String sex, int age) {
        this.name = name;
        this.sex = sex;
        this.age = age;
    }
    public People() {
    }
    @Override
    public String toString() {
        return "People{" +
                "name='" + name + '\'' +
                ", sex='" + sex + '\'' +
                ", age=" + age +
                '}';
    }
}

定义子类Student

public class Student extends People{
    private String StudentNum;
    private String School;

    public String getStudentNum() {
        return StudentNum;

    }

    public void setStudentNum(String studentNum) {
        StudentNum = studentNum;
    }

    public String getSchool() {
        return School;
    }

    public void setSchool(String school) {
        School = school;
    }

    public void run(){
        System.out.println("me run");
    }

    public Student(String studentNum, String school,String name,String age,int sex) {
        super(name,age,sex);//这个一个构造器;
        this.StudentNum = studentNum;
        this.School = school;
    }

    public Student() {
    }

    @Override
    public String toString() {
        return "Student{" +
                "StudentNum='" + StudentNum + '\'' +
                ", School='" + School + '\'' +
                '}'+super.toString();
    }
}

在main函数值中student对象调用run()是Student类中的方法.

Student student=new Student("22222","你的大学","小明","女",5);
        student.run();

但是很多方法都可能要用到父类People中的私有成员变量而子类得不到如toString方法

People中的toString方法
public String toString() {
        return "People{" +
                "name='" + name + '\'' +
                ", sex='" + sex + '\'' +
                ", age=" + age +
                '}';
  Student中的tostring方法
  public String toString() {
            return "Student{" +
                    "StudentNum='" + StudentNum + '\'' +
                    ", School='" + School + '\'' +
                    '}'}

因为无法的到父类People中的私有成员变量所以得不到想要的name sex age .而且调用父类中get方法来赋值会和子类中get方法覆盖,从而get方法被无限调用.在这种情况下我们引入了关键字super,super.get();调用的是父类里面的方法,也可以调用里面的变量.

子类构造器

在子类中的构造方法中加上super(父类的变量域)就可以实现对超类的构造器的调用`

 public People(String name, String sex, int age) {
        this.name = name;
        this.sex = sex;
        this.age = age;
    }
    
       public Student(String studentNum, String school,String name,String age,int sex) {
        super(name,age,sex);//这个一个构造器;
        this.StudentNum = studentNum;
        this.School = school;
    }
    
    Student student=new Student("22222","你的大学","小明","女",5);

注意

super调用构造器必须是子类构造器的第一条语句