java - Java で JPanel を使用して長方形を描画する

Question

次のコードの何が問題になっていますか? 長方形が表示されないのはなぜですか

public class SynapsePermanencesViewer {

public JPanel createContentPane(Region region) {
JPanel synapseLayer = new JPanel();
synapseLayer.setLayout(null);

Column[][] columns = region.getColumns();

JPanel redSquare = new JPanel();
Color color = new Color(128, 0, 0);
redSquare.setBackground(color);
int squareLength = 50;
redSquare.setSize(squareLength, squareLength);

// calculate the correct location
redSquare.setLocation(150, 150); // <==== This square isn't displaying WHY???

synapseLayer.setOpaque(true);
return synapseLayer;
}

public SynapsePermanencesViewer(Region region) {
JFrame frame = new JFrame("Synapse Permanences Viewer");

frame.setContentPane(this.createContentPane(region));

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible(true);
}

public static void main(String[] args) {
Region parentRegion = new Region("parentRegion", 2, 2, 1, 20, 1);
Region childRegion = new Region("childRegion", 4, 4, 1, 20, 3);
RegionToRegionConnect connectType = new RegionToRegionRectangleConnect();
connectType.connect(childRegion, parentRegion, 0, 0);

SynapsePermanencesViewer object = new SynapsePermanencesViewer(parentRegion);
}

}