uni/inf1000/hw1/MinOppgave1.java

import java.util.ArrayList;
import java.util.Scanner;
import java.util.Random;

//A 2D vector, with an x and a y property
class Vec2 {
	public int x;
	public int y;

	public Vec2(int vx, int vy) {
		x = vx;
		y = vy;
	}
}

//A ball, with a velocity and position
class Ball {
	public Vec2 pos;
	public Vec2 vel;
	public final String img = "0";

	public Ball(int x, int y, int vx, int vy) {
		pos = new Vec2(x, y);
		vel = new Vec2(vx, vy);
	}

	//Update the ball's position, according to its velocicty
	public void update() {
		pos.x += vel.x;
		pos.y += vel.y;
	}
}

//An arena full of balls
class Arena {
	private Vec2 dimensions;
	private ArrayList<Ball> balls;
	private final String ANSI_CLS = "\u001b[2J";
	private final String ANSI_HOME = "\u001b[H";

	public Arena(int w, int h) {
		dimensions = new Vec2(w, h);
		balls = new ArrayList<Ball>();
	}

	public void addBall(Ball b) {
		balls.add(b);
	}

	//Update all balls, reversing their velocity if they collide with walls
	public void update() {
		for (Ball b: balls) {
			if (b.pos.x + b.vel.x <= 0 || b.pos.x + b.vel.x >= dimensions.x) {
				b.vel.x *= -1;
			}
			if (b.pos.y + b.vel.y < 0 || b.pos.y + b.vel.y >= dimensions.y) {
				b.vel.y *= -1;
			}

			b.update();
		}
	}

	public void draw() {
		//Buffer to avoid drawing to the screen a billion times
		String str = "";

		//Draw top part of frame
		str += " ";
		for (int i = 0; i < dimensions.x; ++i) {
			str += "-";
		}
		str += "\n";

		//Draw all balls
		for (int y = 0; y < dimensions.y; ++y) {
			str += "|";
			for (int x = 0; x < dimensions.x; ++x) {

				//Draw a ball if there's a ball in this square
				boolean isBall = false;
				for (Ball b: balls) {
					if (b.pos.x == x && b.pos.y == y) {
						isBall = true;
						str += b.img;
						break;
					}
				}

				//Draw blank if there's no ball here
				if (!isBall)
					str += " ";
			}
			str += "|\n";
		}

		//Draw bottom part of frame
		str += " ";
		for (int i = 0; i < dimensions.x; ++i) {
			str += "-";
		}

		//Clear the screen and print
		System.out.print(ANSI_CLS + ANSI_HOME + str);
	}
}

class MinOppgave1 {
	private static Arena arena;
	private static final Random rand = new Random();

	//Random int in range
	private static int randInt(int min, int max) {
		return rand.nextInt((max - min) + 1) + min;
	}

	//Overloading randInt to let us exclude a number if we want
	private static int randInt(int min, int max, int exclude) {
		int r;
		do {
			r = rand.nextInt((max - min) + 1) + min;
		} while (r == exclude);

		return r;
	}

	//We generally don't want user input to be 0 or negative
	private static int getPositiveInt(Scanner s) {
		int i = s.nextInt();

		if (i <= 0) {
			System.out.println("Please only input positive integers.");
			System.exit(1);
		}

		return i;
	}

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);

		//Get arena width, arena height, and the amount of balls from the user
		System.out.println("Insert arena width");
		int width = getPositiveInt(s);
		System.out.println("Insert arena height");
		int height = getPositiveInt(s);
		System.out.println("How many balls do you want?");
		int nBalls = getPositiveInt(s);

		arena = new Arena(width, height);

		//Add balls to the arena, with a random position and velocity
		for (int i = 0; i < nBalls; ++i) {
			arena.addBall(new Ball(
				randInt(0, width),  //X
				randInt(0, height), //Y
				randInt(-4, 4, 0),  //Velocity X
				randInt(-2, 2, 0)   //Velocity Y
			));
		}

		//Update the arena (moving the balls, etc), draw the result,
		//and sleep for 33 milliseconds to get an animation at about 30 FPS
		while (true) {
			arena.update();
			arena.draw();

			try {
				Thread.sleep(33);
			} catch (Exception e) {
				System.out.println("Failed to sleep.");
				System.exit(1);
			}
		}
	}
}