Collision Detection between two images in Java

I have two characters displayed in a game I am writing, the player and the enemy. defined as such:

public void player(Graphics g) {
    g.drawImage(plimg, x, y, this);
}

public void enemy(Graphics g) {
    g.drawImage(enemy, 200, 200, this);
}

Then called with:

player(g);
enemy(g);

I am able to move player() around with the keyboard, but I am at a loss when trying to detect a collision between the two. A lot of people have said to use Rectangles, but being a beginner I cannot see how I would link this into my existing code. Can anyone offer some advice for me?