Java06面向对象02

封装

package com.mingmao.javaobjectoriented.programming;

/*
封装的意义：
提高安全性
隐藏代码实现细节
统一接口，形成规范
提高系统的可维护性
 */
//学生类
public class StudentEncapsulation {
    //封装主要是封装属性，方法封装用的很少,private
    //属性私有，只有本类中可使用
    private String name;  //姓名
    private int id;    //学号
    private char sex;    //性别
    private int age;    //年龄

    //获取姓名
    public String getName(){
        return this.name;
    }
    //设置姓名
    public void setName(String name){
        this.name=name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public char getSex() {
        return sex;
    }

    public void setSex(char sex) {
        this.sex = sex;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        if(age>130 || age<0){
            System.out.println("您输入的年龄有误，请重新输入");
        }else{
            this.age = age;
        }
    }
}

package com.mingmao.javaobjectoriented.programming;

public class Application {
    public static void main(String[] args) {
        StudentEncapsulation student=new StudentEncapsulation();

        student.setName("mingmao");
        System.out.println(student.getName());

        student.setAge(200);

    }
}

继承的概念

查看继承树：Navigat-Type Hierarchy

package com.mingmao.javaobjectoriented.programming.inherit;

/*
修饰符：
public:跨包，跨类
protected:本类，本包，不同包的子类
default:默认，可以不写，同一个包内可访问
private:只有本类可访问
 */
//在Java中，都直接或间接默认继承Object类
//Java中只有单继承，没有多继承
//父类
public class Person {
    //public int money=10_0000_0000;
    private int money=10_0000_0000;

    public int getMoney() {
        return money;
    }
    public void setMoney(int money) {
        this.money = money;
    }

    public void say(){
        System.out.println("说了一句话");
    }
}

package com.mingmao.javaobjectoriented.programming.inherit;

//继承，子类
//子类继承了父类，会拥有父类所有方法
public class Student extends Person {
}

package com.mingmao.javaobjectoriented.programming.inherit;

//继承，子类
public class Teacher extends Person{
}

package com.mingmao.javaobjectoriented.programming;

import com.mingmao.javaobjectoriented.programming.inherit.Student;

public class Application {
    public static void main(String[] args) {

        Student student=new Student();
        System.out.println(student.getMoney());
        student.say();
    }
}

继承-super详解

package com.mingmao.javaobjectoriented.programming.inherit1;

public class Person {
    protected String name="mingmao";

    public Person() {
        System.out.println("person无参构造器执行了");
    }

    protected void print(){
        System.out.println("person");
    }

}

package com.mingmao.javaobjectoriented.programming.inherit1;

public class Student extends Person {
    private String name="mingmao1";

    public Student() {
        //隐藏代码，默认调用了父类的无参构造
        // super(); //调用父类的构造方法
        System.out.println("student无参构造器执行了");
    }

    public void printMethod(){
        print(); //调用本类的print方法
        this.print();//调用本类的print方法
        super.print();//调用父类的print方法
    }

    public void printName(String name){
        System.out.println(name);//传参
        System.out.println(this.name);//本类属性
        System.out.println(super.name);//父类属性
    }

    protected void print(){
        System.out.println("student");
    }
}

package com.mingmao.javaobjectoriented.programming;

import com.mingmao.javaobjectoriented.programming.inherit1.Student;

public class Application {
    public static void main(String[] args) {
        Student student=new Student();

        /*
        person无参构造器执行了
        student无参构造器执行了
         */
        student.printName("mingmao2");
        /*
        mingmao2
        mingmao1
        mingmao
         */

        student.printMethod();
        /*
        student
        student
        person
         */
    }
}

继承-方法重写

提前了解多态

package com.mingmao.javaobjectoriented.programming.inherit2;

public class B {
    public static void test(){
        System.out.println("B=>test");
    }
}

package com.mingmao.javaobjectoriented.programming.inherit2;

//重写都是方法的重写，和属性无关
public class A extends B {

    public static void test(){
        System.out.println("A=>test");
    }
}

package com.mingmao.javaobjectoriented.programming;

import com.mingmao.javaobjectoriented.programming.inherit2.A;
import com.mingmao.javaobjectoriented.programming.inherit2.B;

public class Application {
    public static void main(String[] args) {

        A a=new A();
        a.test();//A=>test

        B b=new B();
        b.test();//B=>test

        //父类的引用指向了子类
        B b1=new A();
        b1.test();//B=>test

        //方法的调用只和左边的类型有关
    }
}

方法重写

上述基础上去掉static
方法重写快捷生成：右键Generate-Override-Methods...

package com.mingmao.javaobjectoriented.programming.inherit3;

public class B {

    public void test(){
        System.out.println("B=>test");
    }
}

package com.mingmao.javaobjectoriented.programming.inherit3;

public class A extends B {

    @Override //此为自动生成的注解，有功能
    public void test() {
        System.out.println("A=>test");
    }
}

package com.mingmao.javaobjectoriented.programming;

import com.mingmao.javaobjectoriented.programming.inherit3.A;
import com.mingmao.javaobjectoriented.programming.inherit3.B;

public class Application {
    public static void main(String[] args) {
        A a=new A();
        a.test();//A=>test

        B b=new B();
        b.test();//B=>test

        B b1=new A();
        b1.test();//A=>test

        /*
        静态方法与非静态方法有很大区别：
        静态方法：与类一起加载，方法的调用只与左边类型有关
        非静态方法：可以重写，方法的调用与右边new的对象有关
         */
    }
}

多态

父类引用指向子类
父类只能调用父类中有的方法
如果父类中的方法被子类重写则执行子类的方法

package com.mingmao.javaobjectoriented.programming.polymorphic;

public class Person {
    public void run(){
        System.out.println("run=>person");
    }
}

package com.mingmao.javaobjectoriented.programming.polymorphic;

public class Student extends Person{
    @Override
    public void run() {
        System.out.println("run=>student");
    }

    public void eat(){
        System.out.println("eat=>student");
    }
}

package com.mingmao.javaobjectoriented.programming;

import com.mingmao.javaobjectoriented.programming.polymorphic.Person;
import com.mingmao.javaobjectoriented.programming.polymorphic.Student;

public class Application {
    public static void main(String[] args) {
        //一个对象的实际类型是确定的
        //new Student;
        //new Person;

        //但是可以指向的引用类型就不确定了
        //父类的引用指向子类
        Student s1=new Student();
        Person s2=new Student();
        Object s3=new Student();

        s1.run();
        s2.run();
        s1.eat();
        //s2.eat();出错

        //总结
        Person p=new Student();

        //父类引用指向子类
        //父类只能调用父类中有的方法
        //如果父类中的方法被子类重写则执行子类的方法
        p.run();

    }
}

学习视频

学习视频