How to Perfectly Center an Application Window and its Contents on a Resizable Screen?

How to Center an Application Window on a Resized Screen

Your question involves two challenges: aligning a bouncing object within a JFrame and determining the exact center of a resizable screen.

Part 1: Aligning a Bouncing Object within a JFrame

From your description, it seems that the bouncing object goes off track by about 10 pixels. This discrepancy is likely due to the misconception that the width and height of a JFrame include only the client area (where you draw). In reality, a JFrame consists of a frame, a JRootPane, a JLayeredPane, and the content pane. Therefore, the actual paintable region is smaller than the JFrame's dimensions.

To account for this, adjust the object's boundaries by subtracting the border width from both the width and height of the JFrame.

Part 2: Determining the Exact Screen Center

Determining the center of a resizable screen requires considering both the frame's dimensions and the content pane's dimensions.

• From the frame's perspective, the center is at 50% of the frame's width and height.
• From the content pane's perspective, the center is at 50% of the content pane's width and height.

Depending on your needs, you may use the center point of either the frame or the content pane.

• To center the frame on the screen, use the Window#setLocationRelativeTo(null) method.
• To align your drawing within the content pane, use the content pane's dimensions.

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