Android java基础_类的继承
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