Android java基础_类的继承_android 类继承(2)


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();
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