Add Triangle exercise

Author: phrdang

src/com/codefortomorrow/intermediate/chapter11/practice/Triangle.java

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+package com.codefortomorrow.intermediate.chapter11.practice;
+
+/*
+Create a class named Triangle that contains the following two methods:
+
+Return true if the sum of any two sides is greater than the third side.
+(This is the definition of a valid triangle.)
+public static boolean isValid(double side1, double side2, double side3)
+
+Return the area of the triangle.
+public static double area(double side1, double side2, double side3)
+
+Write a test program that reads three sides for a triangle
+and computes the area if the sides form a valid triangle.
+Otherwise, it displays that the input is invalid.
+Use Heron's Formula to calculate the area of a triangle given 3 sides.
+
+Adapted from Exercise 6.19, Introduction to Java Programming (Comprehensive),
+10th ed. by Y. Daniel Liang
+*/
+
+public class Triangle {
+    public static void main(String[] args) {
+        // test methods here
+    }
+
+    // write methods here
+}

src/com/codefortomorrow/intermediate/chapter11/solutions/Triangle.java

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+package com.codefortomorrow.intermediate.chapter11.solutions;
+
+import java.util.Scanner;
+
+/*
+Create a class named Triangle that contains the following two methods:
+
+Return true if the sum of any two sides is greater than the third side.
+(This is the definition of a valid triangle.)
+public static boolean isValid(double side1, double side2, double side3)
+
+Return the area of the triangle.
+public static double area(double side1, double side2, double side3)
+
+Write a test program that reads three sides for a triangle
+and computes the area if the sides form a valid triangle.
+Otherwise, it displays that the input is invalid.
+Use Heron's Formula to calculate the area of a triangle given 3 sides.
+
+Adapted from Exercise 6.19, Introduction to Java Programming (Comprehensive),
+10th ed. by Y. Daniel Liang
+*/
+
+public class Triangle {
+    public static void main(String[] args) {
+        // prompt user to enter triangle side lengths
+        Scanner input = new Scanner(System.in);
+        
+        System.out.print("Enter side 1: ");
+        double side1 = input.nextDouble();
+
+        System.out.print("Enter side 2: ");
+        double side2 = input.nextDouble();
+
+        System.out.print("Enter side 3: ");
+        double side3 = input.nextDouble();
+
+        input.close();
+
+        // if sides form a valid triangle, print area
+        // else, print error message
+        if (isValid(side1, side2, side3)) {
+            double area = area(side1, side2, side3);
+            System.out.println("The area of the triangle is: " + area);
+        } else {
+            System.out.println("Invalid input. Those sides don't form a triangle.");
+        }
+    }
+
+    /**
+     * Returns whether the given side lengths form a valid triangle
+     * @param side1  triangle's first side
+     * @param side2  triangle's second side
+     * @param side3  triangle's third side
+     * @return true if the given side lengths form a valid triangle
+     */
+    public static boolean isValid(double side1, double side2, double side3) {
+        return (side1 + side2 > side3) &&
+            (side1 + side3 > side2) &&
+            (side2 + side3 > side3);
+    }
+
+    /**
+     * Returns the area of a triangle given its three side lengths
+     * @param side1  triangle's first side
+     * @param side2  triangle's second side
+     * @param side3  triangle's third side
+     * @return the area of the triangle
+     */
+    public static double area(double side1, double side2, double side3) {
+        // calculate semiperimeter
+        double s = (side1 + side2 + side3) / 2;
+
+        // return area
+        return Math.sqrt(s * (s - side1) * (s - side2) * (s - side3));
+    }
+}