第2课第3节_Java面向对象编程_继承性_P【学习笔记】

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摘要:韦东山android视频学习笔记

面向对象程序的三大特性之继承性：继承性的主要作用就是复用代码.继承性也有一定的限制，如图一

图一

1、我们在第2课第2节_Java面向对象编程_封装性_P 中定义了persion.我在这代码基础上定义一个学习类，并继承persion类。

 1 class Persion{
 2     private int age;
 3 
 4     public void setAge(int age){
 5         if (age < 0 || age > 200)
 6             age = 0;
 7         else
 8             this.age = age;
 9     }
10 
11     public int getAge(){
12         return age;
13     }
14 }
15 
16 class Student extends Persion{
17 
18 }
19 
20 public class Ext{
21     public static void main(String args[]){
22         Student stu = new Student();
23         stu.setAge(10);
24 
25         System.out.println(stu.getAge());
26         
27     }
28 }

编译运行结果

2、在上面的代码基础上，我们的子类继承了父类，我们可以添加自己的属性还有方法.

 1 class Persion{
 2     private int age;
 3 
 4     public void setAge(int age){
 5         if (age < 0 || age > 200)
 6             age = 0;
 7         else
 8             this.age = age;
 9     }
10 
11     public int getAge(){
12         return age;
13     }
14 }
15 
16 class Student extends Persion{
17     private String school;
18 
19     public void setSchool(String school){
20         this.school = school;
21     }
22 
23     public String getSchool(){
24         return school;
25     }
26 
27     public Student(String school){
28         this.school = school;
29     }
30     
31 
32 }
33 
34 public class Ext2{
35     public static void main(String args[]){
36         Student stu = new Student("ustc");
37         stu.setAge(10);
38 
39         System.out.println(stu.getAge());
40         System.out.println(stu.getSchool());
41         
42     }
43 }

编译运行结果

3、子类继承父类的方法和属性都可以进行覆写，我们在子类覆写父类的printInfo方法。

 1 class Persion{
 2     private int age;
 3 
 4     public void setAge(int age){
 5         if (age < 0 || age > 200)
 6             age = 0;
 7         else
 8             this.age = age;
 9     }
10 
11     public int getAge(){
12         return age;
13     }
14 
15     public void printInfo(){
16         System.out.println("age = " + age);
17     }
18 }
19 
20 class Student extends Persion{
21     private String school;
22 
23     public void setSchool(String school){
24         this.school = school;
25     }
26 
27     public String getSchool(){
28         return school;
29     }
30 
31     public Student(String school){
32         this.school = school;
33     }
34 
35     public void printInfo(){
36         System.out.println("school = " + school + " age = " + getAge());
37     }
38 }
39 
40 public class Ext3{
41     public static void main(String args[]){
42         Student stu = new Student("ustc");
43         stu.setAge(10);
44 
45         System.out.println(stu.getAge());
46         System.out.println(stu.getSchool());
47         stu.printInfo();
48         
49     }
50 }

编译运行结果

第2课第3节_Java面向对象编程_继承性_P【学习笔记】

4、实例化子类对象时，先调用父类的构造方法，再调用子类的构造方法，super（）函数在子类中可以指定调用父类构造函数的类型。

 1 class Persion{
 2     private int age;
 3 
 4     public void setAge(int age){
 5         if (age < 0 || age > 200)
 6             age = 0;
 7         else
 8             this.age = age;
 9     }
10 
11     public int getAge(){
12         return age;
13     }
14 
15     public void printInfo(){
16         System.out.println("age = " + age);
17     }
18 
19     public Persion(){System.out.println("Persion()");};
20     public Persion(int age){
21         System.out.println("Persion(int age)");
22         this.age = age;
23     }    
24 }
25 
26 class Student extends Persion{
27     private String school;
28 
29     public void setSchool(String school){
30         this.school = school;
31     }
32 
33     public String getSchool(){
34         return school;
35     }
36 
37     public Student(String school){
38         super(5);
39         System.out.println("Student(String school)");
40         this.school = school;
41     }
42 
43     public void printInfo(){
44         System.out.println("school = " + school + " age = " + getAge());
45     }
46 }
47 
48 public class Ext4{
49     public static void main(String args[]){
50         Student stu = new Student("ustc");
51         //stu.setAge(10);
52 
53         System.out.println(stu.getAge());
54         System.out.println(stu.getSchool());
55         stu.printInfo();
56         
57     }
58 }

编译运行结果

5、抽象类规定子类必须实现的方法，起“模板”作用，缺点不能实例化对象，子类必须覆写全部抽象方法

 1  abstract class Father {
 2     private int money;    
 3 
 4     public int getMoney() {return money; }
 5     public void setMoney(int money) {this.money = money; }
 6 
 7     public abstract void study();
 8 }
 9 
10 class Son extends Father{
11     public void study() {System.out.println("I am study"); }
12     
13 }
14 
15 public class Ext6 {
16     public static void main (String args[]) {
17         //Father f = new Father();
18         Son son = new Son();
19         son.study();
20 
21     }
22 }

编译运行结果：

6、作用：跟抽象类相似，起“模板”作用；子类可以继承多个接口，突破“单继承”的限制

 1 abstract class Father{
 2     private int money;
 3 
 4     public int getMoney(){return money;}
 5     public void setMoney(int money){
 6         this.money = money;
 7     }
 8     public abstract void study();
 9 }
10 
11 
12 interface A{
13     public static final int i = 10;
14     public abstract int getNum();
15 }
16 
17 interface B{
18     public static String name = "InterfaceB";
19     public abstract String getName();
20 }
21 
22     
23 
24 class Son extends Father implements A,B{
25     public int getNum(){return i;}
26     public String getName(){return name;}
27     
28     public void study(){
29         System.out.println("I am study");
30     }
31 }
32 
33 
34 public class Ext6{
35     public static void main(String args[]){
36         Son son = new Son();
37         System.out.println(son.getName());
38         System.out.println(son.getNum());
39         son.study();
40         
41     }
42 }

编译运行结果：

相关代码存放在github，可以下载https://github.com/zzb2760715357/100ask

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第2课第3节_Java面向对象编程_继承性_P【学习笔记】

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