ch05java高级类特性.docx

1、ch05java高级类特性第5章 高级类特性第一节 抽象类与抽象方法一、类的类型类的类型：最终类(final)、抽象类(abstract)、默认类。抽象类(abstract) 一个abstract类不能直接创建对象,必须通过其子类才能创建对象。最终类(final) 一个最终类不能再派生子类。默认类 可以有子类，也可以生成对象。二、抽象(abstract)类1.抽象方法抽象方法是指只给出定义,但不包含实现语句的方法。抽象方法它没有大括号，有大括号但大括号中没有任何内容的方法，仍不是抽象方法。如：public abstract void lx();2.抽象类的概念用abstract修饰的类称为抽象

2、类。一般的抽象类都包括抽象方法.这种类不能创建对象，因为它的完整实现还没有定义。只能由其创建子类(抽象类是专门用来作为其它类的父类的)。3.抽象类的定义在类定义的class关键词前放置关键词abstract即可。格式：abstract class 类名如：public abstract class Student String id; String name; String speciality; public Student(String id, String name,String speciality ) this.id=id; this.name=name; this.speciali

3、ty=speciality; / public Student( )/ this.id=null;/ this.name=null;/ this.speciality=null;/ public void setId(String id) this.id=id; public String getId() return id; public String getName() return name; public void setName(String name) this.name = name; public String getSpeciality() return speciality

4、; public void setSpeciality(String speciality) this.speciality = speciality; public String getStudentInfo() return id=+getId() +name=+getName() +speciality=+getSpeciality(); public abstract int sum();public class AgricultureStudent extends Student private int botany; private int gengzuo; public Agri

5、cultureStudent(String id, String name,String speciality ,int botany,int gengzuo) /*父类没定义构造方法或有无参构造方法 super();/super可省略 / this.id=id;/ this.name=name;/ this.speciality=speciality; /this.botany=botany; */ /父类有参数时 super(id,name,speciality); this.botany=botany; this.gengzuo=gengzuo; public int getBotany

6、() return botany; public void setBotany(int botany) this.botany = botany; Override public String getStudentInfo() return super.getStudentInfo() +score=+getBotany(); Override public int sum() return gengzuo+botany; public class StudentTest public static void main(String args) AgricultureStudent agicu

7、ltureStudent=new AgricultureStudent(123, li,agriculture,90,67); System.out.println(id+agicultureStudent.getId() +sum=+agicultureStudent.sum(); /* * 没有抽象方法的抽象类 * author tai */public abstract class ABDemo int age = 10; void setAge(int a) age = a; public static void main(String a) ABDemo a1 = new ABDem

8、o();/此命令会出错,抽象类不能生成对象 4、实例public class Polymorphism public static void main(String args) Triangle t=new Triangle(5.0,2.0); t.show_area(); Rectangle r=new Rectangle(3.0,4.0); r.show_area(); Circle c=new Circle(10.0); c.show_area(); abstract class Figure protected double x=10.0,y=5.0; abstract void sh

9、ow_area();class Triangle extends Figure Triangle(double a,double b) x=a; y=b; void show_area() System.out.println(triangle:+(0.5*x*y); class Rectangle extends Figure Rectangle(double a,double b) x=a; y=b; void show_area() System.out.println(rectangle:+(x*y); class Circle extends Figure Circle(double

10、 a)x=a; final double pi=3.1416; void show_area() System.out.println(circle:+(pi*x*x); 实例二、public abstract class Math int answer; void show() System.out.print(answer+answer); abstract void add(int a,int b);/计算a+b abstract void sub(int a,int b);/计算a-b abstract void mul(int a,int b);/计算a+b abstract voi

11、d div(int a,int b);/a/bclass Compute extends Math /在此类里继承了show void add(int a, int b) answer = a + b; void sub(int a, int b) answer = a - b; void mul(int a, int b) answer = a * b; void div(int a, int b) answer = a / b; public class App public static void main(String args) Compute cmp=new Compute();

12、cmp.add(3, 5); cmp.show(); 强调： 抽象类的子类必须在类中实现抽象类中的抽象方法，即给出抽象方法的定义,它才不是抽象类。5、强调将类Triangle方法中的show_area()去掉，前必须加abstract关键字，为什么?因为类Triangle没有对show_area()进行重写，而是直接继承了抽象方法public class Polymorphism public static void main(String args) Triangle t=new Triangle(5.0,2.0); t.show_area(); Rectangle r=new Rectan

13、gle(3.0,4.0); r.show_area(); Circle c=new Circle(10.0); c.show_area(); abstract class Figure protected double x=10.0,y=5.0; abstract void show_area();abstract class Triangle extends Figure Triangle(double a,double b) x=a; y=b; class Rectangle extends Figure Rectangle(double a,double b) x=a; y=b; voi

14、d show_area() System.out.println(rectangle:+(x*y); class Circle extends Figure Circle(double a)x=a; final double pi=3.1416; void show_area() System.out.println(circle:+(pi*x*x); 强调：不使用抽象类，如果子类没有覆盖超类中的非抽象方法，也不会出错，但没有意义 抽象类可否有自己的构造方法? 答案是: 抽象类中允许有自己的构造方法,但是该构造方法并不能直接实例化自己的对象. 如果在抽象类中存在有参构造方法,则必须在子类中明确

15、的使用super(参数列表)指明要调用父类中的哪个构造方法.四、为什么要使用抽象类1、抽象类是规范为了使抽象类的子类在完成相同或相似的功能时，具有相同的方法名。(在规化类库时，在抽象类中定义出抽象方法，使实现它的子类的程序员去实现。2、代码重用可以继承.3、多态为了实现多态。第二节 抽象类与多态一、实例一abstract class Figure protected double x=10.0,y=5.0; abstract void show_area();class Triangle extends Figure Triangle(double a,double b) x=a; y=b;

16、void show_area() System.out.println(triangle:+(0.5*x*y); class Rectangle extends Figure Rectangle(double a,double b) x=a; y=b; void show_area() System.out.println(rectangle:+(x*y); class Circle extends Figure Circle(double a)x=a; final double PI=3.1416; void show_area() System.out.println(circle:+(P

17、I*x*x); 测试一：public class Test1 public static void main(String args) / Figure f=new Triangle(5.0,2.0);/ f.show_area();/ f=new Rectangle(3.0,4.0);/ f.show_area();/ f=new Circle(10.0);/ f.show_area(); 测试二：public class Test2 public static void main(String args) Figure f =new Figure3;/为什么 f0=new Triangle

18、(5.0,2.0); f1=new Rectangle(6.0,87.0); f2=new Circle(100.0); for(Figure f1:f) f1.show_area(); 测试三：public class Test3 public static void show(Figure f) f.show_area(); public static void main(String args) Triangle triangle = new Triangle(5.0, 2.0); Rectangle rectangle = new Rectangle(3.0, 4.0); Circle

19、 circle = new Circle(10.0); show(triangle); show(circle); show(rectangle); 测试四：public class Test4 public static void show(Rectangle rec) for(Rectangle rectangle:rec) rectangle.show_area(); public static void main(String args) Rectangle rectangle = new Rectangle2; rectangle0 = new Rectangle(3.0, 4.0)

20、; rectangle1 = new Rectangle(5.0, 4.0); show(rectangle); 二、实例二abstract class Figure protected double x=10.0,y=5.0; abstract double area();class Rectangle extends Figure Rectangle(double a,double b) x=a; y=b; double area() return (x*y); class Triangle extends Figure double z; Triangle(double a,double

21、 b,double c) x=a; y=b; z=c; double area() double p=(x+y+z)/2; return Math.sqrt(p*(p-x)*(p-y)*(p-z); class Circle extends Figure Circle(double a)x=a; double area() return Math.PI*x*x; 测试一：public class Test4 public static double totalArea1(Figure f) double totalArea=0; for(Figure f1:f) totalArea+=f1.a

22、rea(); return totalArea; public static void main(String args) Figure f =new Figure3;/为什么 f0=new Triangle(5.0,6.0,7.0); f1=new Rectangle(6.0,87.0); f2=new Circle(100.0); double totalArea=0; for(Figure f1:f) totalArea+=f1.area(); System.out.println(totalarea=+totalArea); System.out.println(totalarea1=

23、+totalArea1(f); 测试二：import javax.swing.JOptionPane;/* * * author tai */public class Test5 public static double totalArea1(Figure f) double totalArea=0; for(Figure f1:f) totalArea+=f1.area(); return totalArea; public static void main(String args) Figure f =new Figure3;/为什么 f0=new Triangle(5.0,6.0,7.0

24、); f1=new Rectangle(6.0,87.0); String input=JOptionPane.showInputDialog(输入圆的半径); double r=Double.parseDouble(input); f2=new Circle(r); double totalArea=0; for(Figure f1:f) totalArea+=f1.area(); JOptionPane.showMessageDialog(null,totalarea=+totalArea); JOptionPane.showMessageDialog(null,totalarea1=+t

25、otalArea1(f); 测试三：import javax.swing.JOptionPane;/* * * author tai */public class Test6 public static double totalArea1(Figure f) double totalArea=0; for(Figure f1:f) totalArea+=f1.area(); return totalArea; public static void main(String args) Figure f =new Figure3;/为什么 f0=new Triangle(5.0,6.0,7.0);

26、 f1=new Rectangle(6.0,87.0); double r; try String input=JOptionPane.showInputDialog(输入圆的半径); r=Double.parseDouble(input); catch(NumberFormatException e) r=0.0; f2=new Circle(r); double totalArea=0; for(Figure f1:f) totalArea+=f1.area(); JOptionPane.showMessageDialog(null,totalarea=+totalArea); JOpti

27、onPane.showMessageDialog(null,totalarea1=+totalArea1(f); 作业：第三节 接口(interface)一、接口的概念接口是和类一种相似又有区别的一种结构，接口的设计和调用也是Java程序设计的重要技术。接口是一种特殊的抽象类接口是一种完全没有实现的类。接口用关键字interface来定义，而不是class；接口中定义的变量都是公用的最终的静态变量(即常量 用public static final 修饰)；接口中没有构造方法，而且定义的方法全是抽象方法(即在方法中只提供方法的定义，而没有提供方法的实现语句)，接口中的方法是用public abstract修饰的。接口采用多重继承机制，而不是采用类的单一继承机制。二、接口的声明接口的格式如下：interface 接口名 常量的定义 方法的说明三、接口的使用-类对接口的继承（实现）class 类名 implements 接口名实例一、public class InterfaceDemo public static void main(String args) /A a=new A();/接口不能生成对象 B b =new B(); b.show(); public interface A double g=9.8; void show();publ