This Java program is from Y. Daniel Liang\'s Introduction to Java Programing, (8

Question

This Java program is from Y. Daniel Liang's Introduction to Java Programing, (8th Edition). Exercise 11.1 on page 403. Design a class named Triangle that extends the GeometricObject. Use the following template: public class Exercise11_01 { public static void main(String[] args) { Triangle triangle = new Triangle(1, 1.5, 1); triangle.setColor("yellow"); triangle.setFilled(true); System.out.println(triangle); System.out.println("The area is " + triangle.getArea()); System.out.println("The perimeter is " + triangle.getPerimeter()); System.out.println(triangle); } } class GeometricObject { // Copy it from the book } class Triangle extends GeometricObject { // Implement it }

Explanation / Answer

class GeometricObject { private String color = "white"; private boolean filled; private java.util.Date dateCreated; public GeometricObject() { 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; } public String toString() { return "created on " + dateCreated + " color: " + color + " and filled: " + filled; } } class Triangle extends GeometricObject { // Three double data fields named side1, side2, and side3 private double side1; private double side2; private double side3; // No-arg constructor that creates the default triangle with 1.0 sides public Triangle() { side1 = 1.0; side2 = 1.0; side3 = 1.0; } // Constructor that creates a triangle with specified side1, side2, and side3 public Triangle(double side1, double side2, double side3) { this.side1 = side1; this.side2 = side2; this.side3 = side3; } // Create accessor methods for all three data fields public double getSide1() { return side1; } public double getSide2() { return side2; } public double getSide3() { return side3; } // Method that returns area of the triangle public double getArea() { return (side1 + side2 + side3) / 2; } // Method that returns the perimeter of the triangle public double getPerimeter() { return side1 + side2 + side3; } // Method that returns a string description for the triangle public String toString() { return "Triangle: side1 = " + side1 + " side2 = " + side2 + " side3 = " + side3; } }

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