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joakimmohn's solution

to Triangle in the Java Track

Published at Oct 08 2019 · 0 comments
Instructions
Test suite
Solution

Determine if a triangle is equilateral, isosceles, or scalene.

An equilateral triangle has all three sides the same length.

An isosceles triangle has at least two sides the same length. (It is sometimes specified as having exactly two sides the same length, but for the purposes of this exercise we'll say at least two.)

A scalene triangle has all sides of different lengths.

Note

For a shape to be a triangle at all, all sides have to be of length > 0, and the sum of the lengths of any two sides must be greater than or equal to the length of the third side. See Triangle Inequality.

Dig Deeper

The case where the sum of the lengths of two sides equals that of the third is known as a degenerate triangle - it has zero area and looks like a single line. Feel free to add your own code/tests to check for degenerate triangles.

Setup

Go through the setup instructions for Java to install the necessary dependencies:

https://exercism.io/tracks/java/installation

Running the tests

You can run all the tests for an exercise by entering the following in your terminal:

$ gradle test

Use gradlew.bat if you're on Windows

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by removing the @Ignore("Remove to run test") annotation.

Source

The Ruby Koans triangle project, parts 1 & 2 http://rubykoans.com

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

TriangleTest.java

import org.junit.Test;
import org.junit.Ignore;
import org.junit.Rule;
import org.junit.rules.ExpectedException;

import static org.junit.Assert.assertTrue;
import static org.junit.Assert.assertFalse;

public class TriangleTest {

    @Rule
    public ExpectedException expectedException = ExpectedException.none();

    @Test
    public void equilateralTrianglesHaveEqualSides() throws TriangleException {
        Triangle triangle = new Triangle(2, 2, 2);

        assertTrue(triangle.isEquilateral());
    }

    @Ignore("Remove to run test")
    @Test
    public void trianglesWithOneUnequalSideAreNotEquilateral() throws TriangleException {
        Triangle triangle = new Triangle(2, 3, 2);

        assertFalse(triangle.isEquilateral());
    }

    @Ignore("Remove to run test")
    @Test
    public void trianglesWithNoEqualSidesAreNotEquilateral() throws TriangleException {
        Triangle triangle = new Triangle(5, 4, 6);

        assertFalse(triangle.isEquilateral());
    }

    @Ignore("Remove to run test")
    @Test
    public void trianglesWithNoSizeAreIllegal() throws TriangleException {
        expectedException.expect(TriangleException.class);
        new Triangle(0, 0, 0);
    }

    @Ignore("Remove to run test")
    @Test
    public void verySmallTrianglesCanBeEquilateral() throws TriangleException {
        Triangle triangle = new Triangle(0.5, 0.5, 0.5);

        assertTrue(triangle.isEquilateral());
    }

    @Ignore("Remove to run test")
    @Test
    public void isoscelesTrianglesHaveLastTwoSidesEqual() throws TriangleException {
        Triangle triangle = new Triangle(3, 4, 4);

        assertTrue(triangle.isIsosceles());
    }

    @Ignore("Remove to run test")
    @Test
    public void isoscelesTrianglesHaveTwoFirstSidesEqual() throws TriangleException {
        Triangle triangle = new Triangle(4, 4, 3);

        assertTrue(triangle.isIsosceles());
    }

    @Ignore("Remove to run test")
    @Test
    public void isoscelesTrianglesHaveFirstAndLastSidesEqual() throws TriangleException {
        Triangle triangle = new Triangle(4, 3, 4);

        assertTrue(triangle.isIsosceles());
    }

    @Ignore("Remove to run test")
    @Test
    public void equilateralTrianglesAreAlsoIsosceles() throws TriangleException {
        Triangle triangle = new Triangle(4, 4, 4);

        assertTrue(triangle.isIsosceles());
    }

    @Ignore("Remove to run test")
    @Test
    public void noSidesAreEqualCantBeIsoceles() throws TriangleException {
        Triangle triangle = new Triangle(2, 3, 4);

        assertFalse(triangle.isIsosceles());
    }

    @Ignore("Remove to run test")
    @Test
    public void firstTriangleInequalityViolation() throws TriangleException {
        expectedException.expect(TriangleException.class);
        new Triangle(1, 1, 3);
    }
    
    @Ignore("Remove to run test")
    @Test
    public void secondTriangleInequalityViolation() throws TriangleException {
        expectedException.expect(TriangleException.class);
        new Triangle(1, 3, 1);
    }
    
    @Ignore("Remove to run test")
    @Test
    public void thirdTriangleInequalityViolation() throws TriangleException {
        expectedException.expect(TriangleException.class);
        new Triangle(3, 1, 1);
    }

    @Ignore("Remove to run test")
    @Test
    public void verySmallTrianglesCanBeIsosceles() throws TriangleException {
        Triangle triangle = new Triangle(0.5, 0.4, 0.5);

        assertTrue(triangle.isIsosceles());
    }

    @Ignore("Remove to run test")
    @Test
    public void scaleneTrianglesHaveNoEqualSides() throws TriangleException {
        Triangle triangle = new Triangle(5, 4, 6);

        assertTrue(triangle.isScalene());
    }

    @Ignore("Remove to run test")
    @Test
    public void allSidesEqualAreNotScalene() throws TriangleException {
        Triangle triangle = new Triangle(4, 4, 4);

        assertFalse(triangle.isScalene());
    }

    @Ignore("Remove to run test")
    @Test
    public void twoSidesEqualAreNotScalene() throws TriangleException {
        Triangle triangle = new Triangle(4, 4, 3);

        assertFalse(triangle.isScalene());
    }

    @Ignore("Remove to run test")
    @Test
    public void mayNotViolateTriangleInequality()
            throws TriangleException {
        expectedException.expect(TriangleException.class);
        new Triangle(7, 3, 2);
    }

    @Ignore("Remove to run test")
    @Test
    public void verySmallTrianglesCanBeScalene() throws TriangleException {
        Triangle triangle = new Triangle(0.5, 0.4, 0.6);

        assertTrue(triangle.isScalene());
    }
}

src/main/java/Triangle.java

class Triangle {
    double side1;
    double side2;
    double side3;

    Triangle(double side1, double side2, double side3) throws TriangleException {
        if(side1 <= 0 || side2 <= 0 || side3 <= 0) {
            throw new TriangleException("A side must have a length");
        }

        if((side1 + side2) < side3 ||
           (side2 + side3) < side1 ||
           (side1 + side3) < side2) {
            throw new TriangleException("One side is too short");
        }

        this.side1 = side1;
        this.side2 = side2;
        this.side3 = side3;
    }

    boolean isEquilateral() {
        return ((side1 == side2) && (side2 == side3));
    }

    boolean isIsosceles() {
        return side2 == side1 || side3 == side1 || side2 == side3;
    }

    boolean isScalene() {
        return !isEquilateral() && !isIsosceles();
    }

    public static void main(String[] args) {
        try {
            Triangle triangle = new Triangle(2, 3, 4);

            System.out.println(triangle.isIsosceles());
        } catch(Exception e) {}
    }
}

src/main/java/TriangleException.java

class TriangleException extends Exception {
    TriangleException(String msg) {
        super(msg);
    } 
}

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?