一.Android Java基础_类的继承

先封装一个persion类，在persion的基础上定义Student类，并基础persion类。

子类能访问父类的成员函数。

class Person {private int age;public void setAge(int age) {if (age < 0 || age > 200)age = 0;else {this.age = age;}}public int getAge() {return age;}	
}class Student extends Person{
}public class Ext {public static void main (String args[]) {Student stu = new Student();stu.setAge(10);System.out.println(stu.getAge());}
}

运行结果：

root@ubuntu:/home/topeet/guyilian# javac Ext.java 
root@ubuntu:/home/topeet/guyilian# java Ext
10

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.

class Person {private int age;public void setAge(int age) {if (age < 0 || age > 200)age = 0;else {this.age = age;}}public int getAge() {return age;}	
}class Student extends Person{private String school;public void setSchool(String school) {this.school = school;}public String getSchool() {return school;}	public Student(String school) {this.school = school;}}public class Ext2 {public static void main (String args[]) {Student stu = new Student("ustc");stu.setAge(10);System.out.println(stu.getAge());System.out.println(stu.getSchool());}
}

运行结果：

root@ubuntu:/home/topeet/guyilian# javac Ext2.java 
root@ubuntu:/home/topeet/guyilian# java Ext2
10
ustc

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。

class Person {private int age;public void setAge(int age) {if (age < 0 || age > 200)age = 0;else {this.age = age;}}public int getAge() {return age;}	public void printInfo() {System.out.println("age = "+age);}
}class Student extends Person{private String school;public void setSchool(String school) {this.school = school;}public String getSchool() {return school;}	public Student(String school) {this.school = school;}/* override */public void printInfo() {System.out.println("school = "+school+"; age = "+getAge());}}public class Ext3 {public static void main (String args[]) {Student stu = new Student("ustc");stu.setAge(10);System.out.println(stu.getAge());System.out.println(stu.getSchool());stu.printInfo();}
}

运行结果：

root@ubuntu:/home/topeet/guyilian# javac Ext3.java 
root@ubuntu:/home/topeet/guyilian# java Ext3
10
ustc
school = ustc; age = 10

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。

class Person {private int age;public void setAge(int age) {if (age < 0 || age > 200)age = 0;else {this.age = age;}}public int getAge() {return age;}	public void printInfo() {System.out.println("age = "+age);}public Person () {System.out.println("Person ()");}public Person (int age) {System.out.println("Person (int age)");this.age = age;}}class Student extends Person{private String school;public void setSchool(String school) {this.school = school;}public String getSchool() {return school;}	public Student(String school) {/* will call the super() *///super();super(5);System.out.println("Student(String school)");this.school = school;}/* override */public void printInfo() {System.out.println("school = "+school+"; age = "+getAge());}}public class Ext4 {public static void main (String args[]) {Student stu = new Student("ustc");//stu.setAge(10);System.out.println(stu.getAge());System.out.println(stu.getSchool());stu.printInfo();}
}

运行结果：

root@ubuntu:/home/topeet/guyilian# javac Ext4.java 
root@ubuntu:/home/topeet/guyilian# java Ext4
Person (int age)
Student(String school)
5
ustc
school = ustc; age = 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。

abstract class Father {private int money;	public int getMoney() {return money; }public void setMoney(int money) {this.money = money; }public abstract void study();
}class Son extends Father{public void study() {System.out.println("I am study"); }}public class Ext6 {public static void main (String args[]) {//Father f = new Father();Son son = new Son();son.study();}
}

运行结果：

root@ubuntu:/home/topeet/guyilian# javac Ext6.java 
root@ubuntu:/home/topeet/guyilian# java Ext6
I am study

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。

abstract class Father {private int money;	public int getMoney() {return money; }public void setMoney(int money) {this.money = money; }public abstract void study();
}class Son extends Father{public void study() {System.out.println("I am study"); }}public class Ext6 {public static void main (String args[]) {//Father f = new Father();Son son = new Son();son.study();}
}

运行结果：

root@ubuntu:/home/topeet/guyilian# javac Ext7.java
root@ubuntu:/home/topeet/guyilian# java Ext7
InterfaceB
I am study