javaSE接口随笔

接口

1. 如何定义抽象类和抽象方法

访问修饰符 abstract class 类名{访问修饰符 abstract 返回值 方法名(参数列表);
}

抽象类不一定有抽象方法，但是有抽象方法的类一定是抽象类

2. 如何定义接口，接口中能定义哪些方法

访问修饰符 interface 接口名{数据类型 变量名 = 变量的值; //接口中定义的变量都是公开的静态常量返回值类型 方法名(参数列表); //接口中定义的方法都是公开的抽象方法default 返回值类型 方法名(参数列表){// 接口中定义的默认方法都是公开的 => JDK1.8//代码块[return 返回值;]}static 返回值类型 方法名(参数列表){// 接口中定义的静态方法都是公开的 => JDK1.8//代码块[return 返回值;]}private 返回值类型 方法名(参数列表){// 接口中定义的默认方法都是公开的 => JDK1.9//代码块[return 返回值;]}
}

接口没有构造方法

3. 抽象类和接口的区别

a. 抽象类是一个类，所以抽象类只能单继承，而接口可以多继承。一个类在继承抽象类的同时还可以实 现一个或多个接口

b. 抽象类拥有构造方法，而接口没有

c. 抽象类中可以定义成员变量和受保护的、受包保护的成员方法，而接口中定义的变量都是公开的静态 常量，接口中定义的方法都是公开的抽象方法

d. 接口主要用于功能性方面的描述，而抽象类更加注重的是抽象事物的描述。

4.代码复现

package Shape;
/*
几何图形*/
public abstract class Shape {public abstract Number perimeter();public abstract Number area();
}package Shape;public class Rectangle extends Shape{private int width;private int length;public Rectangle(int width, int length) {this.width = width;this.length = length;}public Integer perimeter() {return (width + length) * 2;}public Integer area() {return width * length;}
}package Shape;public class Circle {private int radius;public Circle(int radius) {this.radius = radius;}public Double perimeter() {return 2 * Math.PI * radius;}public Double area() {return Math.PI * radius * radius;}
}package Shape;public class ShapeTest {public static void main(String[] args) {Rectangle r1 = new Rectangle(10,8);System.out.println(r1.perimeter());System.out.println(r1.area());Circle c1 = new Circle(10);System.out.println(c1.perimeter());System.out.println(c1.area());}
}

package Person;public interface Person {String getName();
}package Person;public interface Actor extends Person {void performance();
}package Person;public interface Artist extends Actor , Singer {void endorsement();
}package Person;public interface Singer extends Person {void sing();
}package Person;public class EntertainmentStar implements Artist {private String name;public EntertainmentStar(String name) {this.name = name;}@Overridepublic void endorsement() {System.out.printf("娱乐明星%s代言\n",  getName());
}@Overridepublic void performance() {System.out.printf("娱乐明星%s表演\n", getName());}@Overridepublic void sing() {System.out.printf("娱乐明星%s唱歌\n", getName());
}@Overridepublic String getName() {return name;}
}package Person;public class PersonTest {public static void main(String[] args) {Person p = new EntertainmentStar("刘德华");System.out.println(p.getName());Actor a = new EntertainmentStar("范冰冰");a.performance();Singer s = new EntertainmentStar("张学友");s.sing();Artist artist = new EntertainmentStar("古天乐");artist.endorsement();artist.performance();artist.sing();}
}

package printer;
/*** 打印机对外暴露有墨盒（颜色）和纸张（大小）接口，墨盒生产商按照墨盒接口的约定生产黑白墨盒和* 彩色墨盒，纸张生产商按照纸张接口的约定生产A2纸和A4纸张。*/
public interface Paper {String getSize();//获取纸张大小
}package printer;public class A4Paper implements Paper{public String getSize() {return "A4Paper";}
}package printer;public class A2Paper implements Paper{public String getSize() {return "A2Paper";}
}package printer;/*** 打印机对外暴露有墨盒（颜色）和纸张（大小）接口，墨盒生产商按照墨盒接口的约定生产黑白墨盒和* 彩色墨盒，纸张生产商按照纸张接口的约定生产A2纸和A4纸张。*/
public interface InkBox {String getColor();
}package printer;import javax.swing.*;public class BlackInkBox implements InkBox {public String getColor(){return "black and white";}
}package printer;import java.awt.*;public class ColorInkBox implements InkBox {public String getColor(){return "彩色";}
}package printer;import java.io.PrintStream;
import java.util.Scanner;public class Printer {private InkBox inkBox;private Paper paper;public Printer(InkBox inkBox, Paper paper) {this.inkBox = inkBox;this.paper = paper;}public Printer() {}public void print() {PrintStream printf = System.out.printf("printer use %s InkBox print on %s paper.\n",inkBox.getColor(), paper.getSize());}public InkBox getInkBox() {return inkBox;}public void setInkBox(InkBox inkBox) {this.inkBox = inkBox;}public Paper getPaper() {return paper;}public void setPaper(Paper paper) {this.paper = paper;}
}package printer;public class PrinterTest {public static void main(String[] args) {Printer p1 = new Printer();p1.setPaper(new A4Paper());p1.setInkBox(new ColorInkBox());p1.print();Printer p2 = new Printer(new BlackInkBox(), new A2Paper());p2.print();}
}