FPS drops after loading images in java

Question

So, I recently asked a question on how to preload images in Java (preloading images in Java) and it worked great! Until I went to play the game. Framerate dropped drastically. I don't know what it was, but basically, I have a whole sprite map loaded into an array. Each image corresponds to a three-degree rotation. So, 5 degrees would become the 3-degree image, 6 would stay the 6, and so on (I tried Math.round and it actually made the 5 and 4-degree images go to the 6-degree image, and that's more desirable, however, it's slower)
I am looking for some ways to optimize the code. Here are my angle calculations:

private float getAngle(double x, double y) {
    float angle = (float) Math.toDegrees(Math.atan2(y - this.getCenterY(), x - this.getCenterX()));
    if(angle < 0){
        angle += 360;
    }
    return angle;
}

The x and y values inputted into the method are the center x and y values of the enemy being targeted by the tower performing this calculation. Then this code is executed in the draw method:

if(airID==Value.towerCannon && (airRow>0 && airRow<5) && angle>=0) {
    if(angle==Canvas.rotatedAirMap.length) angle = 0;
        g.drawImage(Canvas.rotatedAirMap[angle][level-1], x, y, width, height, null); 
    } else {
        g.drawImage(Canvas.airMap[airRow][airID], x, y, width, height, null); 
    }
}

This will draw the appropriate, preloaded image rotated at the specified angle (The "angle" - or image identifier - is calculated when the tower shoots by dividing the result of the angle calculation by three and then casting that to an int - I could also round that value)
Any suggestions on how to optimize this so I don't get such massive frame drops? I assume the frame drops are due to the VM heap size being too small, but I've increased it and still, nothing significant happens. Any help would be greatly appreciated.
Thanks!

@VGR here is what I did with your response:

public void paintComponent(Graphics g) {
    if(isFirst) { //Define stuff when isFirst is true
        define(); //Sets up the image arrays

        GraphicsConfiguration config = getGraphicsConfiguration();
        if(config == null) {
            GraphicsEnvironment env = GraphicsEnvironment.getLocalGraphicsEnvironment();
            config = env.getDefaultScreenDevice().getDefaultConfiguration();
        }

        BufferedImage compatibleImage = config.createCompatibleImage(image.getWidth(), image.getHeight(), image.getTransparency());

        g = compatibleImage.createGraphics();

        isFirst = false;
    }
}

This works a little bit faster, but I had to do some workarounds. repaint() is called in the game loop (this class implements runnable) So the graphics component created by the repaint method (however that works) is the graphics I use for the whole game. Would this be the correct way to do it?

Answer 1

Translating images from their inherent color model to the color model of the current video mode can slow down rendering. To avoid this, you can make sure each image is compatible with the screen where your window resides:

BufferedImage image = ImageIO.read(/* ... */);

GraphicsConfiguration config = getGraphicsConfiguration();
if (config == null) {
    GraphicsEnvironment env = GraphicsEnvironment.getLocalGraphicsEnvironment;
    config = env.getDefaultScreenDevice().getDefaultConfiguration();
}

BufferedImage compatibleImage = config.createCompatibleImage(
    image.getWidth(), image.getHeight(), image.getTransparency());

Graphics2D g = compatibleImage.createGraphics();
g.drawImage(image, 0, 0, null);
g.dispose();

image = compatibleImage;

If an image has the same color model as the current video mode, there is no translation needed when drawing it. It’s even possible that painting of such an image may be done entirely by the GPU.