方法的重写(重点) 多态

方法的重写(重点)

重写:需要有继承关系,子类重写父类的方法!

1.方法名必须相同

2.参数列表必须系统

3.修饰符:范围可以扩大但不能缩小:public>protected>default>private

4.抛出的异常:范围,可以被缩小,但不能扩大:ClassNotFoundException-->Exception(大)

重写:子类的方法和父类必须要一致,方法体不同!

为什么需要重写:

1.父类的功能:子类不一定需要或不一定满足!

alt+ins:override

多态

package oop.demo07;

public class Person {
    public void run(){
        System.out.println("run");
    }
}
package oop.demo07;

public class Student extends Person {
}
package oop.demo07;

public class Teacher extends Person{
}
package oop;


import oop.demo07.Person;
import oop.demo07.Student;
import oop.demo07.Teacher;


public class Application {
    //静态方法和非静态方法区别很大!
    //静态方法:  //方法的调用之和左边,定义的数据类型有关
//非静态:重写
    public static void main(String[] args) {

        //Object>Person>Student
        //Object>Person>Teacher
        //Object>String
        Object object = new Student();
        System.out.println(object instanceof Student);//true
        System.out.println(object instanceof Person);//true
        System.out.println(object instanceof Object);//true
        System.out.println(object instanceof Teacher);//False
        System.out.println(object instanceof String);//False
        System.out.println("=====================================");
        Person person = new Student();
        System.out.println(person instanceof Student);//true
        System.out.println(person instanceof Person);//true
        System.out.println(person instanceof Object);//true
        System.out.println(person instanceof Teacher);//False
        //System.out.println(person instanceof String);//编译报错
        System.out.println("=====================================");
        Student student = new Student();
        System.out.println(student instanceof Student);//true
        System.out.println(student instanceof Person);//true
        System.out.println(student instanceof Object);//true
        //System.out.println(student instanceof Teacher);//编译报错
        //System.out.println(student instanceof String);//编译报错

    }


}

System.out,println(X instanceof Y);//能不能编译通过 取决于XY之间是否有父子关系

package oop.demo07;

public class Person {
    public void run(){
        System.out.println("run");
    }
}
package oop.demo07;

public class Student extends Person {
    public void go(){
        System.out.println("go");
    }
}
package oop.demo07;

public class Teacher extends Person{
}
package oop;


import oop.demo07.Person;
import oop.demo07.Student;
import oop.demo07.Teacher;


public class Application {
    //静态方法和非静态方法区别很大!
    //静态方法:  //方法的调用之和左边,定义的数据类型有关
//非静态:重写
    public static void main(String[] args) {
        //类型之间的转化:  父 子

        //高                     低
        Person obj = new Student();

        //student将这个对象转换为Student类型,我们就可以使用Student类型的方法了

        //子类转换为父类可能会丢失一些方法
        Student student = new Student();
        student.go();
        Person person=student;
        person.run();
        //低                      高
        //强制类型转换另一种写法((Student) obj).go();


    }


}

多态:

1.父类引用指向子类的对象

2.把子类转换为父类,向上转型

3.把父类转换为子类,向下转型,强制转换

4.方便方法的调用,减少重复的代码!

抽象三大特性:1.封装、继承、多态!static

posted @ 2020-12-17 22:05  XC666  阅读(108)  评论(0)    收藏  举报