摘要:韋東山android視頻學(xué)習(xí)筆記?

面向?qū)ο蟪绦虻娜筇匦灾^承性：繼承性的主要作用就是復(fù)用代碼.繼承性也有一定的限制，如圖一

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圖一

1、我們在第2課第2節(jié)_Java面向?qū)ο缶幊蘝封裝性_P 中定義了persion.我在這代碼基礎(chǔ)上定義一個學(xué)習(xí)類，并繼承persion類。

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 }

編譯運行結(jié)果

2、在上面的代碼基礎(chǔ)上，我們的子類繼承了父類，我們可以添加自己的屬性還有方法.

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 }

編譯運行結(jié)果

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3、子類繼承父類的方法和屬性都可以進行覆寫，我們在子類覆寫父類的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 }

編譯運行結(jié)果

4、實例化子類對象時，先調(diào)用父類的構(gòu)造方法，再調(diào)用子類的構(gòu)造方法，super（）函數(shù)在子類中可以指定調(diào)用父類構(gòu)造函數(shù)的類型。

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 }

編譯運行結(jié)果

?5、抽象類規(guī)定子類必須實現(xiàn)的方法，起“模板”作用，缺點不能實例化對象，子類必須覆寫全部抽象方法

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 }

編譯運行結(jié)果：

6、作用：跟抽象類相似，起“模板”作用；子類可以繼承多個接口，突破“單繼承”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 }

編譯運行結(jié)果：

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相關(guān)代碼存放在github，可以下載https://github.com/zzb2760715357/100ask?

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轉(zhuǎn)載于:https://www.cnblogs.com/zzb-Dream-90Time/p/10897430.html

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