Homework 1, Part A: Area of a Triangle

Goals:

Practice with:

• working with BlueJ IDE to write, compile, run simple java programs
• java primitive data types, expressions and operators
• defining and calling methods
• selecting testing values to determine whether program will work in all possible cases

Description

Write a program, AreaTriangle, that prompts the user three times for the side lengths of a triangle. Based on these three inputs, the program checks and prints whether this triangle is isosceles or not, as well as its area. In addition to the main method, your program should also define three other static methods:

1. a predicate method isValidTriangle to check whether the three inputs define a triangle, based on the triangular inequality (that is, the sum of any two sides of a triangle is strictly greater than the third side),
2. a method to getHeronArea compute the triangle’s area based on Heron’s Formula given the three side lengths,
3. a predicate method isIsosceles to check whether the triangle is isosceles

Some important notes on this exercise:

• Equilateral triangles are considered isosceles.
• If the user enters three side lengths that cannot possibly form a triangle (ex. 1,1,2), your program should say that this set of input does not form a triangle and stop execution.
• You do not need to handle the case when the user enters other invalid input, e.g. negative number(s) or non-numbers.

Starter Code

Please use the starter code below:

AreaTriangle.java:

// Import the necessary library (Scanner), to read user-inputted text
import java.util.Scanner;

public class AreaTriangle
{
    public static boolean isValidTriangle(double a, double b, double c) {
        return false; // TODO replace this with your implementation
    }
    
    public static boolean isIsosceles(double a, double b, double c) {
        return false; // TODO replace this with your implementation
    }
    
    public static double getHeronArea(double a, double b, double c) {
        return 0.0; // TODO replace this with your implementation
    }
    
    public static void main(String[] args) {
        // Create a "scanner," used to read user-inputted text
        Scanner scanner = new Scanner(System.in);

	// Read in a user-inputted double from the text prompt
        System.out.print("Please enter first side: ");
        double a = scanner.nextDouble();

        System.out.print("Please enter second side: ");
        double b = scanner.nextDouble();

        System.out.print("Please enter third side: ");
        double c = scanner.nextDouble();

        if (!isValidTriangle(a, b, c)) {
            System.out.println("This is not a valid triangle.");
            return;
        }
        
        if (isIsosceles(a, b, c)) {
            System.out.println("The triangle is isosceles.");
        } else {
            System.out.println("The triangle is NOT isosceles.");
        }
        
        System.out.println(
            "The area of the triangle is: " + getHeronArea(a, b, c)
        );
    }
}

Testing your program

Think carefully about the set of inputs (testing cases) you will provide to your program to assert its correctness. Your inputs should be such that every method you wrote is tested (invoked) as your program runs.

To show work for your testing, please run the program with many different inputs that trigger every execution path. For each run, save the results of your testing produced in the “BlueJ: Terminal Window” into a .txt file (Options > Save to File…). Finally, compose a file called AreaTriangleTest.txt containing the outputs of each of your test runs.

What to submit

It is a standard policy of this course that submissions that have not been signed (@author) and dated (@version) will not be graded.

Your Gradescope submission should contain the following:

1. your AreaTriangle.java file
2. your AreaTriangleTest.txt file that contains your testing results

Homework 1, Part B: Fun with Loops

Goals:

Practice with:

• working with BlueJ IDE to write, compile, run simple java programs
• java primitive data types, expressions and operators
• practicing loops
• selecting testing values

Description

In this exercise, you will learn how to use different types of loops in your code, based on the needs of that program. You are given the starter code below, and your goal is to fill in the body of the empty methods with logic based on the descriptions provided here. Make sure to also provide the appropriate javadoc at the top of the file.

FunLoops.java:

/**
 * Write a description of class Funloops here.
 *
 * @author (write your name here)
 * @version (write a version number or a date here)
 */

public class FunLoops{

  /**
  * Part 1 of the exercise.
  * This method should act like a toddler who knows their numbers, once they 
  * are given a number, they start reciting all numbers from 1 to that number.
  * Only one number should be printed per line.
  * @param theNum the input number
  */
  public static void toddler(int theNum){

  }

  /**
  * Part 2 of the exercise.
  * Given a number, this method prints a right-angled triangle of stars. 
  * The height and base of that triangle should consist of a number of stars 
  * equal to the input number.
  * @param theNum the input number
  */
  public static void dreamer(int theNum){
    
  }
  
  /**
  * Part 3 of the exercise.
  * Given a number, this method prints a right-angled triangle of stars.
  * Unlike the "dreamer", this method prints out a triangle that was
  * horizontally flipped.
  * @param theNum the input number
  */
  public static void sleeper(int theNum){
    
  }

  public static void main(String[] args){
    System.out.println("\nNow calling toddler(6)");
    toddler(6);
    
    System.out.println("\nNow calling dreamer(4)");
    dreamer(4);
    
    System.out.println("\nNow calling Sleeper(6)");
    sleeper(6);
  }
}

Part 1: The toddler. Complete the method toddler in the starter code provided for you. This method will be given a number as parameter and it will list out all numbers from 1 to that number. The method should print out each number on their own line.

Part 2: The dreamer. Complete the method dreamer in the starter code provided for you. This method will be given a number as parameter and then it will draw a right-angled triangle of stars. The height and base of that triangle will consist of a number of stars equal to the input number. For example, given the number 4, this method should print:

*
**
***
****

Part 3: The sleeper. Complete the method sleeper in the starter code provided for you. This method is the same as dreamer, but prints the triangle horizontally flipped. That is, given the number 4, it should print:

   *
  **
 ***
****

While there are many ways to implement this method, we ask you to take the following approach:

1. First, implement a helper method, sleeperHelper, that takes in two integers, a and b. This method should print out a spaces followed by b stars (all on the same line).
2. After having created (and tested) this helper function, use it to implement sleeper.

Please note:

• We recommend you start by writing on a piece of paper how the three methods should work. You need to know what your correct answer should look like before you program!
• The sample main we have provided is not complete, in the sense that it does not show all the calls to the methods. To test them you should call each one multiple times.
• You should test each method you implemented above separately. They should not depend on each other.
• Some methods can be implemented using more than one type of loop. We will accept all correct answers, as long as the code is not overly complicated.

Testing your program

Think carefully about the set of inputs (testing cases) you will provide to your program to assert its correctness. Your inputs should be such that every method you wrote is tested (invoked) as your program runs.

In BlueJ, save the results of your testing produced in the “BlueJ: Terminal Window” into a file called loopsTest.txt. (Options > Save to File…)

What to submit

It is a standard policy of this course that submissions that have not been signed (@author) and dated (@version) will not be graded.

Your Gradescope submission should contain the following:

1. your FunLoops.java source file
2. your loopsTest.txt text file that contains your testing results

Submission Checklist

• You submitted all .java files and all .txt files.
• Your files are named exactly as in the homework specification, including file extensions.
• You tested every possible pathway in your code.
• You signed every class (or file) with @author and @version, accompanied by a description of what the class does.
• You wrote javadoc for every function, which includes @param and @return.
• You wrote inline comments explaining the logic of your code.