设计抽象类GeometricObject及其子类Triangle和Circle。 GeometricObject类设计要求如下： ■ 一个名为color 的Color类型的私有数据域，表示对象的颜色。 ■ 一个名为filled 的Boolean类型的私有数据域，表示对象是否填充颜色。 ■ 一个名为dateCreated的Date类型的私有数据域，表示对象的创建日期。 ■ 一个无参构造方法。 ■ 一个能创建特定color 和filled 的有参构造方法。 ■ 相关数据域的访问器和修改器。 ■ 两个个名为draw和erase的抽象方法。 ■ 一个名为getArea的抽象方法。 ■ 一个名为getPerimeter的抽象方法。 ■ 重写toString方法。 java

抽象类GeometricObject的实现如下：

import java.util.Date;
import java.awt.Color;

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

Triangle子类的实现如下：

public class Triangle extends GeometricObject {
    private double side1;
    private double side2;
    private double side3;
    
    public Triangle(double side1, double side2, double side3, Color color, boolean filled) {
        super(color, filled);
        this.side1 = side1;
        this.side2 = side2;
        this.side3 = side3;
    }
    
    public double getSide1() {
        return this.side1;
    }
    
    public void setSide1(double side1) {
        this.side1 = side1;
    }
    
    public double getSide2() {
        return this.side2;
    }
    
    public void setSide2(double side2) {
        this.side2 = side2;
    }
    
    public double getSide3() {
        return this.side3;
    }
    
    public void setSide3(double side3) {
        this.side3 = side3;
    }
    
    @Override
    public void draw() {
        System.out.println("Drawing triangle...");
    }
    
    @Override
    public void erase() {
        System.out.println("Erasing triangle...");
    }
    
    @Override
    public double getArea() {
        double s = (this.side1 + this.side2 + this.side3) / 2;
        return Math.sqrt(s * (s - this.side1) * (s - this.side2) * (s - this.side3));
    }
    
    @Override
    public double getPerimeter() {
        return this.side1 + this.side2 + this.side3;
    }
}

Circle子类的实现如下：

public class Circle extends GeometricObject {
    private double radius;
    
    public Circle(double radius, Color color, boolean filled) {
        super(color, filled);
        this.radius = radius;
    }
    
    public double getRadius() {
        return this.radius;
    }
    
    public void setRadius(double radius) {
        this.radius = radius;
    }
    
    @Override
    public void draw() {
        System.out.println("Drawing circle...");
    }
    
    @Override
    public void erase() {
        System.out.println("Erasing circle...");
    }
    
    @Override
    public double getArea() {
        return Math.PI * this.radius * this.radius;
    }
    
    @Override
    public double getPerimeter() {
        return 2 * Math.PI * this.radius;
    }
}