java语言程序设计 第十三章 抽象类与接口 （13.1）

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public abstract class GeometricObject{    private String color;    private boolean filled;    private java.util.Date dateCreated;    protected GeometricObject()    {        dateCreated = new java.util.Date();    }    protected GeometricObject(String color, boolean isFilled)    {        this.color = color;        this.filled = filled;        dateCreated = new java.util.Date();    }    public String getColor()    {        return color;    }    public void setColor(String color)    {        this.color = color;    }    public boolean isFilled()    {        return filled;    }    public void setFilled(boolean filled)    {        this.filled = filled;    }    public java.util.Date getDateCreated()    {        return dateCreated;    }    @Override    public String toString()    {        return "created on " + dateCreated + "\ncolor: " + color + "\nand filled: " + filled;    }    public abstract double getArea();    public abstract double getPerimeter();}

public class TriangleException extends Exception{    private double side1;    private double side2;    private double side3;    public TriangleException(double side1, double side2, double side3)    {        super("Can't create a triangle.");        this.side1 = side1;        this.side2 = side2;        this.side3 = side3;    }    public double getSide1()    {        return side1;    }    public double getSide2()    {        return side2;    }    public double getSide3()    {        return side3;    }}

// 为了练习异常的声明，写了一个TriangleException，其实没必要，只要用 if 判断给出错误信息就好public class Triangle extends GeometricObject{    private double side1;    private double side2;    private double side3;    public Triangle()    {    }    public Triangle(double side1, double side2, double side3) throws TriangleException    {        this(side1, side2, side3, "white", false);    }    public Triangle(double side1, double side2, double side3, String color, boolean filled)        throws TriangleException    {        super(color, filled);        this.side1 = side1;        this.side2 = side2;        this.side3 = side3;        judge(side1, side2, side3);    }    public double getSide1()    {        return side1;    }    public void setSide1(double side1)    {        this.side1 = side1;    }    public double getSide2()    {        return side2;    }    public void setSide2(double side2)    {        this.side2 = side2;    }    public double getSide3()    {        return side3;    }    public void setSide3(double side3)    {        this.side3 = side3;    }    @Override    public double getArea()    {        double side = (side1 + side2 + side3) / 2;        double area = Math.sqrt(side * (side - side1) * (side - side2) * (side - side3));        return area;    }    @Override    public double getPerimeter()    {        return (side1 + side2 + side3);    }    private void judge(double side1, double side2, double side3) throws TriangleException    {        if ((side1 + side2 <= side3) || (side1 - side2 >= side3))        {            throw new TriangleException(side1, side2, side3);        }    }}

import java.util.Scanner;public class TsetTriangle{    public static void main(String [] args)    {        Scanner input = new Scanner(System.in);        System.out.print("Enter side1 : ");        double side1 = input.nextDouble();        System.out.print("Enter side2 : ");        double side2 = input.nextDouble();        System.out.print("Enter side3 : ");        double side3 = input.nextDouble();        System.out.print("Enter a color : ");        String color = input.next();        System.out.print("Is filled ? ");        boolean filled = input.nextBoolean();        try        {            Triangle triangle = new Triangle(side1, side2, side3, color, filled);            System.out.println("Area : " + triangle.getArea());            System.out.println("Perimeter : " + triangle.getPerimeter());        }        catch (TriangleException ex)        {            System.out.println(ex.getMessage());        }    }}