Write a program that prompts the user to enter three points of a triangle and displays the angles in degrees. Round the value to keep two digits after the decimal point.

5-23.java

import java.awt.Point;
import java.io.IOException;
 
public class Angles {
  public static void main(String[] args) throws IOException {
		//1 1 6.5 1 6.5 2.5
		double[] numbers = new double[0];
		
		while(numbers.length != 6) try {
			System.out.print("Enter three points: ");
			numbers = parseInput(readInput());
			//catch error on incorrect number of inputs
			if(numbers.length != 6) {
				System.out.println("Incorrect number of inputs. 6 numbers are required, 2 for each point.");
			}
		} catch(NumberFormatException e) {
			//catch error on non-number input
			String msg = e.getMessage();
			msg = msg.substring(msg.indexOf('"'), msg.lastIndexOf('"')+1);
			System.out.printf("The input %s is not a recongizable number.\n",msg);
		}
		
		// Calculate sides
		double a = Point.distance(numbers[2], numbers[3], numbers[4], numbers[5]);
		double b = Point.distance(numbers[0], numbers[1], numbers[4], numbers[5]);
		double c = Point.distance(numbers[0], numbers[1], numbers[2], numbers[3]);
		
		// Calculate angles
		double A = Math.acos((a*a-b*b-c*c)/(-2.0*b*c));
		double B = Math.acos((b*b-a*a-c*c)/(-2.0*a*c));
		double C = Math.acos((c*c-b*b-a*a)/(-2.0*a*b));
		
		//Convert angles to degrees
		A = Math.toDegrees(A);
		B = Math.toDegrees(B);
		C = Math.toDegrees(C);
		
		System.out.printf("The three angles are %.2f %.2f %.2f\n",A,B,C);
		
	}
	
	public static String readInput() throws IOException {
		byte[] buffer = new byte[64];
		int count = System.in.read(buffer);
		String input = new String(buffer,0,count);
		return input;
	}
	
	public static double[] parseInput(String input) {
		String[] split = input.split(" +");
		double[] output = new double[split.length];
		for(int i = 0; i < split.length; ++i)
			output[i] = Double.parseDouble(split[i]);
		return output;
	}
}