title: Setting divider location on a JSplitPane doesn't work
body: <p>I'm trying to set the divider location of a JSplitPane but it seems not to work. </p>
  
  <p>Here's an SSCCE:</p>
  
  <pre><code>import java.awt.Color;
  import javax.swing.BoxLayout;
  import javax.swing.JFrame;
  import javax.swing.JPanel;
  import javax.swing.JSplitPane;
  
  
  public class JSplitProblem extends JFrame {
  
      public JSplitProblem(){
          JPanel upperPanel = new JPanel();
          upperPanel.setLayout(new BoxLayout(upperPanel, BoxLayout.X_AXIS));
  
          JPanel leftPanel = new JPanel();
  
          leftPanel.setLayout(new BoxLayout(leftPanel, BoxLayout.Y_AXIS));
          JPanel red = new JPanel();
          red.setBackground(Color.red);
          leftPanel.add(red);
  
          JPanel rightPanel = new JPanel();
          rightPanel.setLayout(new BoxLayout(rightPanel, BoxLayout.Y_AXIS));
          JPanel blue = new JPanel();
          blue.setBackground(Color.blue);
          rightPanel.add(blue);
  
          upperPanel.add(leftPanel);
          upperPanel.add(rightPanel);
          JPanel bottomPanel = new JPanel();
          bottomPanel.setBackground(Color.black);
  
          JSplitPane mainSplittedPane = new JSplitPane(JSplitPane.VERTICAL_SPLIT, upperPanel,bottomPanel);
          mainSplittedPane.setOneTouchExpandable(true);
          mainSplittedPane.setDividerLocation(0.5);
  
          this.add(mainSplittedPane);
          this.setSize(800,600);
          this.setResizable(true);
          this.setVisible(true);
      }
  
      public static void main(String[] args) {
          new JSplitProblem();
      }
  
  }
  </code></pre>
  
  <p>I would like the black bottom panel to lay on a 50% of the whole area by default. What am I doing wrong?</p>