抽象类
- 用abstract关键字来修饰一个类时,这个类叫做抽象类;用abstract来修饰一个方法时,该方法叫做抽象方法
- 含有抽象方法的类必须被声明为抽象类,抽象类必须被继承,抽象方法必须被重写
- 抽象类不能被实例化
- 抽象方法只需声明,而不需实现
abstract class Animal {
private String name;
Animal(String name){
this.name = name;
}
public abstract void enjoy();
}
class Cat extends Animal {
private String eyeColor;
Cat(String n, String c) {
super(n);
eyeColor = c;
}
public void enjoy() {
System.out.println("猫叫声");
}
}
final关键字
- final的变量的值不能够被改变
- final的成员变量
- final的局部变量(无参)
- final的方法不能够被重写
- final的类不能够被继承
接口
- 多个无关的类可以实现同一个接口
- 一个类可以实现多个无关的接口
- 与继承关系类似,接口与实现类之间存在多态性
- 接口(interfaace)是抽象方法和常量值得定义的集合
- 从本质上讲,接口是一种特殊的抽象类,这种抽象类中只包含常量和方法的定义,而没有变量和方法的实现。
- 定义举例:
public interface Runner {
public static final int id = 1;
public void start();
public void run();
public void stop();
}
- 接口可以多重实现
- 接口中声明的属性默认为public static final的;也只能是public static final的
- 接口中只能定义抽象方法,而且这些方法默认为public的、也只能是public的
- 接口可以继承其他接口,并添加新的属性和抽象方法
- 接口举例:
interface Singer {
public void sing();
public void sleep();
}
interface Painter {
public void paint();
public void eat();
}
class Student implements Singer {
private String name;
Student(String name) {
this.name = name;
}
public void study() {
System.out.println("studying");
}
public void sing() {
System.out.println("student is singing");
}
public void sleep() {
System.out.println("student is sleeping");
}
public String getName() {
return name;
}
}
class Teacher implements Singer, Painter {
private String name;
public String getString() {
return name;
}
Teacher(String name) {
this.name = name;
}
public void teach() {
System.out.println(“teaching);
}
public void sing() {
System.out.println("teacher is singing");
}
public void sleep() {
System.out.pritln("teacher is sleeping");
}
public void paint() {
System.out.println("teacher is painting");
}
public void eat() {
System.out.println("teacher is eating");
}
}
public class Test {
public static void main(String args[]) {
Singer s1 = new Student("le");
s1.sing();
s1.sleep();
Singer s2 = new Teacher("steven");
s2.sing();
s2.sleep();
Painter p1 = (Painter)s2;
p1.paint();
p1.eat();
}
}