american-identity-project/American-Identity-Project/Enemy.java

import java.util.*;
import javax.swing.ImageIcon;

public class Enemy extends Collidable {
  int xVelo, yVelo;
  boolean alive;

  public Enemy(int x, int y, int w, int h, int level) {
    super(x, y, w, h, new ImageIcon("Sprites/Enemies/" + level + ".png"));
    xVelo = 2;
    yVelo = 0;
    alive = true;
  }

  public void moveX(int moveX) {
    this.x += moveX;
    this.rect.x = this.x;
  }

  public void moveY(int moveY) {
    this.y += moveY;
    this.rect.y = this.y;
  }

  public void patrol(ArrayList<Collidable> collidables) {
    moveX(xVelo);

    for (Collidable c : collidables) {
      if (this.collidesWith(c)) {
        xVelo = -xVelo;
        moveX(xVelo * 2);
        break;
      }
    }

    // check edge detection - is there ground below next step?
    boolean edgeAhead = true;
    int nextX = this.x + xVelo;
    for (Collidable c : collidables) {
      if (c instanceof Tile) {
        Tile t = (Tile) c;
        // check if tile is below enemy's next position
        if (nextX + this.width > t.x && nextX < t.x + t.width && t.y == this.y + this.height) {
          edgeAhead = false;
          break;
        }
      }
    }
    if (edgeAhead) {
      xVelo = -xVelo;
    }
  }
}