类的继承与多态

package cn.mooc.student;

//父类
class Person{
    //属性
    private String name;
    private String gender;
    private String location;
    private int age;
    //构造方法
    public Person() {
        System.out.println("Person() run!");
    }
    public Person(String name){
        System.out.println("Person(name) run!");
        this.name = name;
    }
    public Person(String name, String gender, String location, int age) {
        System.out.println("Person(*) run!");
        this.name = name;
        this.gender = gender;
        this.location = location;
        this.age = age;
    }
    //方法set get
    public void setName(String name) {
        this.name = name;
    }
    public String getName(){
        return this.name;
    }
    public String getGender() {
        return gender;
    }
    public void setGender(String gender) {
        this.gender = gender;
    }
    public String getLocation() {
        return location;
    }
    public void setLocation(String location) {
        this.location = location;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }

    //方法eat
    public void eat(Person p){
        System.out.println(p.name+" is eatting!");
    }
    //方法toString(对于Object类toString方法的复写)
    public String toString() {
        return "Person [name=" + name + ", gender=" + gender + ", location="
                + location + ", age=" + age + "]";
    }
}

//子类
public class Student extends Person {
    //属性
    private int credit;
    private String name;
    //构造方法
    public Student(){}
    public Student(int credit,String name) {
        super(name);
        this.credit = credit;
        System.out.println("Student(*) run");
        //this.name = name;
        //若子类没有父类属性,则默认调用父类空参(此时父类若无空参,就会报错)
    }
    //方法get
    public int getCredit(){
        return this.credit;
    }
    //方法set
    public void setCredit(int credit){
        this.credit = credit;
    }
    //方法study
    public void study(Student s){
        System.out.println(s.getName()+" is studying!");
    }
    //方法toString
    public String toString(){
        return "name="+name+"::credit="+credit;
    }

    public static void main(String[] args) {
        Person p1 = new Person("Lily","female","America",20);
        //Student s1 =  (Student) p1;
        //System.out.println(s1.toString());
        //1,ClassCastException父类不能转为子类
        
        Student s1 = new Student(16,"Luck");
        s1.setName("GG");//调用父类的方法改变父类属性,但不影响自身的属性
        s1.setAge(22);
        System.out.println(s1.toString());
        //2,子类可以调用父类方法,当父类和子类有相同方法时,优先调用子类自己的方法
        
        p1.toString();
        //3,父类不能调用子类方法
        //综上,子类获取了父类所有的属性和方法,但如果有与自己相同的方法,调用时优先调用自身属性方法
    }
}

Person(*) run!
Person(name) run!
Student(*) run
name=null::credit=16

可以看出.子类的创建伴随着对父类相应构造器的调用

父类相应的构造方法,通过super(parameters)传递到子类