How to calculate area of triangle in Java Program? Example

Writing a Java program to calculate the area of a triangle is one of the basic programming exercises to develop a coding sense for beginner programmers. Like many mathematical conceptual programs e.g. square root, factorial, or prime number this also serves as a good exercise for beginners. Now, if you remember in maths you might have seen two main ways to calculate the area of a triangle, using vertices and using base and height. In this program, I have created two methods to calculate the area of a triangle using both ways. 

In the first method area(Point a Point b, Point c)  we expect coordinates of three vertices of the triangle and then we calculate the area of the triangle using the formula (Ax(By -Cy) + Bx(Cy -Ay) + Cx(Ay - By))/2, while in the second method, area(int base, int height) we expect the value of base and height and then we calculate are of the triangle using formula (base * height) / 2.

Calculating the area of a triangle using 3 points

In this program, you need to write a method that accepts three points, you can create a Point class to encapsulate both X and Y coordinates and then calculate the area of the triangle using the following formula:

Area of triangle =  (Ax(By -Cy) + Bx(Cy -Ay) + Cx(Ay - By))/2

Here A, B,and C are three vertices of the triangle and x and y represent coordinates. 

Calculating area of a triangle using base and height

This one is easier to remember as you might have used this formula lot many times before. In this part of the program, you write a method that expects two integer values to capture base and height and return a float which is the area of a triangle.

We'll use the following formula:

Area of triangle = (base * height) / 2

Where the base is the length of the base and height is the height of the triangle as shown in the following diagram:

Now that you know the formulas to calculate the area of a triangle in Java, we'll see the code which implements these formulas. Remember, you can use these formulas to calculate the area of any type of triangle e.g. right-angle triangle, equilateral triangle, etc. These are generic formulas and work for all types of triangles.

Java Program to calculate the area of a triangle

Here is our complete Java program to find the area of a triangle given base and height or points of three vertices. I have created a Point class to represent a point that has both X and Y coordinates and two overloaded area() methods to calculate the area of a triangle. 

The first area() method expects three parameters, which are points of three vertices and then it return a float value which is the area of a triangle. The second area() method takes base and height and returns a float value which is the area of a triangle.

/*
 * Java Program to calculate area of triangle using co-ordinates of vertices
 * or by using base and height. 
 */

public class Main {

  public static void main(String[] args) {
    Point A = new Point(13, 34);
    Point B = new Point(22, 21);
    Point C = new Point(11, 19);
    System.out.println("area of triangle using formula 1: "
        + Triangle.area(A, B, C));
    System.out.println("area of triangle using formula 2: "
        + Triangle.area(3, 5));

  }

}

class Point {
  int x;
  int y;

  public Point(int x, int y) {
    this.x = x;
    this.y = y;
  }

}

class Triangle {

  /**
   * Java method to return area of triangle using vertices as per following
   * formula area = (Ax(By -Cy) + Bx(Cy -Ay) + Cx(Ay - By))/2
   * 
   * @return
   */
  public static float area(Point A, Point B, Point C) {
    float area = (A.x * (B.y - C.y) 
                    + B.x * (C.y - A.y) + C.x * (A.y - B.y)) / 2.0f;
    return Math.abs(area);
  }

  /**
   * 
   * @param base
   * @param height
   * @return
   */
  public static float area(int base, int height) {
    return (base * height) / 2.0f;
  }
}

Output
area of triangle using formula 1: 80.5
area of triangle using formula 2: 7.5

That's all about how to calculate the area of a triangle in Java. This is a good exercise to learn to program along with many others which I have shared below. We have learned both ways to calculate the area of a triangle in the program i.e. using 3 points of vertices as well as by using the base and height formula. 

Othe Java Programs you may like to practice

• Fibonacci series in Java
• Prime number checking in Java
• String Palindrome Problem
• Number Palindrome Problem
• Armstrong number Checking
• Calculating Factorial in Java
• Reverse String Problem
• Calculating GCD in Java
• Leap year Problem

You can further read Concrete Mathematics: A Foundation for Computer Science to learn more about how mathematics plays an important role in Computer Science and programming.