http://programmingpraxis.com/2013/01/18/triangle-trilemma/

Triangle.java

public class Triangle {

  public static String identifyTriangle(Point w, Point r, Point t) {
		double A, B, C;
		double angA, angB, angC;
		String sideClass, angleClass;
		
		A = distance(w, r);
		B = distance(w, t);
		C = distance(r, t);
		
		//Check valid triangle
		if(area(w, r, t) == 0){
			return "Not a triangle";
		}
		
		if(A == B && A == C){
			sideClass = "equilateral";
		} else if(A == B || A == C || B == C){
			sideClass = "isosceles";
		} else {
			sideClass = "scalene";
		}
		
		//cos rule
		angC = Math.toDegrees(Math.acos(Math.toRadians((Math.pow(A, 2) + Math.pow(B, 2) - Math.pow(C, 2)) / (2 * A * B))));
		//sin rule
		angA = Math.toDegrees(Math.asin(A * Math.sin(Math.toRadians(angC)) / C));
		//triangle is 180degrees
		angB = 180 - angA - angC;
		
		
		if(angA == 90 || angB == 90 || angC == 90){
			angleClass = "right";
		} else if(angA > 90 || angB > 90 || angC > 90){
			angleClass = "obtuse";
		} else {
			angleClass = "acute";
		}
		
		return sideClass + " " + angleClass + " triangle";
	}
	
	public static double distance(Point w, Point r){
		return Math.sqrt(Math.pow(w.x - r.x, 2) + Math.pow(w.y - r.y, 2));
	}
	
	public static double area(Point w , Point r, Point t){
		return (w.x*(r.y - t.y)) + (r.x*(t.y - w.y)) + (t.x*(w.y - r.y));
	}
	
}