6.java三大特征之一：继承，super与this

Myth丶恋晨 2024-04-01 19:33 70阅读 0赞

①封装

将属性和方法书写到类里面的操作就是封装

封装可以为属性和方法添加私有权限

②继承

子类默认继承父类的所有属性和方法

子类可以重写父类属性和方法

③多态

传入不同的对象，产生不同的结果

## 继承 ##

两个类的属性和方法有很多重叠，继承可以解决代码的复用问题

![afca998af80a4754a9689ec48ba73199.png][]

继承案例

package extend;
    //学生
    public class Student {
        public String name;
        public int age;
    
        private double score;//成绩
        public void setScore(double score) {
            this.score = score;
        }
        public void showInfo() {
            System.out.println("名字"+name+"年龄"+age+"成绩"+score);
        }
    }

package extend;
    //小学生
    public class Pupil extends Student{
        public void testing(){
            System.out.println("小学生"+name);
        }
    }

package extend;
    //大学生
    public class  Graduate extends Student{
        public void testing(){
            System.out.println("小学生"+name);
        }
    }

package extend;
    
    public class Test {
        public static void main(String[] args) {
            Pupil pupil = new Pupil();
            Graduate graduate = new Graduate();
            pupil.name = "qqq";
            pupil.age = 11;
            pupil.setScore(11.1);
            pupil.showInfo();
        }
    }

细节

例如：上面代码setScore

![fcd879ad023643cbb191f3bd41432791.png][]

![02a6207457534d89a285285a96d91894.png][]

package extend;
    
    public class Test {
        public static void main(String[] args) {
            Pupil pupil = new Pupil();
            Pupil pupil1 = new Pupil("jack");
        }
    }

package extend;
    //学生
    public class Student {
        public Student(){
            System.out.println("父类无参。。。");
        }
        public Student(String name){
            System.out.println("父类有参。。。");
        }
    }

ackage extend;
    //小学生
    public class Pupil extends Student{
        public Pupil(){
            super("name");
    //        super();//默认调用
            System.out.println("子类无参。。。");
        }
    
        public Pupil(String jack) {
            super("name");
            System.out.println("子类有参。。。");
        }
    }

![6f71305350dd47f9b60e882be4aed4fa.png][]

ctrl+h查看可以查看类的继承关系

![9122f82c1ab542e3bd45e876c7d982b5.png][]

![7fbdc400e5aa41ce9571a791feda39f0.png][]

先加载类，在方法区显示继承关系

![819327e034874e09aaecca04b6475e04.png][]

![2ff935e6c5464d9c8febf5bda44bb9f3.png][]

package extend;
    
    public class Test {
        public static void main(String[] args) {
            Son son = new Son();
            System.out.println(son.name);
        }
    
    }
    class GrandPa{
        String name = "LJW";
        String address = "徐州";
    }
    class Father extends GrandPa{
        String name = "QYJ";
        int age = 33;
    }
    class Son extends Father{
        String name = "SJB";
    
    }

### super ###

![b89e6b1ee95146aabc43219d4fce295b.png][]

![1e15ad5053144d95b568ce81ba37242a.png][]

### super与this ###

![3ffa46f6a73748a988998cc631d57ad1.png][]

[afca998af80a4754a9689ec48ba73199.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/8b4b277af16c495dbefddc13c855df41.png
[fcd879ad023643cbb191f3bd41432791.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/a9498f9835ed4dd9b24f698becff9423.png
[02a6207457534d89a285285a96d91894.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/52c36705f07a4a54ad3e5a0c2131c117.png
[6f71305350dd47f9b60e882be4aed4fa.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/2fe139e7214c4c498f88866d5ff6307a.png
[9122f82c1ab542e3bd45e876c7d982b5.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/e1275e103ff94b28b41405ee144bdfeb.png
[7fbdc400e5aa41ce9571a791feda39f0.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/80ac87eb85c941c8b1f38566edda9833.png
[819327e034874e09aaecca04b6475e04.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/af193ff3083942f9a748cd2809db4248.png
[2ff935e6c5464d9c8febf5bda44bb9f3.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/eeb4d7d789114dcaa4edd04c84d602a7.png
[b89e6b1ee95146aabc43219d4fce295b.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/bad76aa43da44f2bb6103c9708db7f5f.png
[1e15ad5053144d95b568ce81ba37242a.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/c0fc83b7f7234ddca4d9c961e9d15308.png
[3ffa46f6a73748a988998cc631d57ad1.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/d52de5228d114600a3b0f41b67efd273.png