Thread: Game moving keys

I want to write simple game. Why if I press button UP and RIGHT it not move diogonally, may be it have special code. And how I need to write correctly border and gravity? (Sorry for my English, it is not my home language).

public class Main {
 
	public static void main(String args[]) {
		JFrame frame = new JFrame("Stickman");
		Ground ground = new Ground();
		frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
		frame.setSize(710, 480);
		frame.add(ground);
		frame.setVisible(true);
		ground.requestFocus();
 
	}
 
 
 
}

public class Ground extends JPanel {
	public Ground() {
 
		addKeyListener(new myKeyAdapter());
 
	}
 
	Image img = new ImageIcon("Resourse/Untitled.jpg").getImage();
	Stickman stk = new Stickman();
 
	private class myKeyAdapter extends KeyAdapter {
		public void keyPressed(KeyEvent e) {
 
			stk.keyPressed(e);
			repaint();
		}
 
		public void keyReleased(KeyEvent e) {
 
			stk.keyReleased(e);
			repaint();
		}
 
	}
 
	public void paint(Graphics g) {
 
		g = (Graphics2D) g;
		g.drawImage(img, stk.sloi1, 0, null);
		g.drawImage(stk.img, stk.x, stk.y, null);
 
 
 
	}
}

public class Stickman {
 
	public static final int MAX_TOP = (4);
	public static final int MAX_BOTTOM = (120);
 
	Image img = new ImageIcon("Resourse/Untitled2.png").getImage();
 
	int x = 5;
	int y = 143;
	int moveAmount = 5;
	int sloi1 = 0;
 
	public void move() {
		if (y <= MAX_TOP)y = MAX_TOP;
		if(y >= MAX_BOTTOM)y = MAX_BOTTOM;
 
	}
 
	public void keyPressed(KeyEvent e) {
		int key = e.getKeyCode();
 
		if (key == KeyEvent.VK_RIGHT) {
			x += moveAmount;
 
 
		}
 
		if (key == KeyEvent.VK_LEFT) {
 
			x -= moveAmount;
 
		}
 
		if (key == KeyEvent.VK_UP) {
 
			y -= 20;
		}
 
	}
 
 
	public void keyReleased(KeyEvent e) {
	}
 
}

Override paintComponent() rather than paint() in a JPanel. For more information, refer to the Oracle Trail on custom painting.