title: Java - Vertical "FlowLayout" with Horizontal Scrolling
body: <p>As described in the title, I've been trying to set up sort of a vertical flow layout with horizontal scrolling.  The components within the layout will be JLabels.  Let me draw a picture:</p>
  
  <pre><code>+-------------------------+   &lt;--- window
  |Label1   Label4    Label7|
  |Label2   Label5    Label8|   &lt;--- labels
  |Label3   Label6    Label9|
  |&lt;===============&gt;========|   &lt;--- scrollbar
  +-------------------------+
  </code></pre>
  
  <p>Same window, expanded vertically</p>
  
  <pre><code>+--------------------------+   &lt;--- window
  |Label1   Label5    Label9 |
  |Label2   Label6    Label10|   &lt;--- labels
  |Label3   Label7    Label11|
  |Label4   Label8    Label12|
  |&lt;===================&gt;=====|   &lt;--- scrollbar
  +--------------------------+
  </code></pre>
  
  <p>So, the labels would fill the available vertical space and then create a new column.  Once the available horizontal space is exhausted, a <strong>horizontal</strong> scrollbar would appear.</p>
  
  <p>A vertical scrollbar should not typically appear; however, it would be nice to have a vertical scrollbar if the vertical height of the window is unusually small.</p>
  
  <p>Any help is greatly appreciated.  I'm new to Java, so any additional explanation would be wonderful.  Thanks!</p>
  
  <p>Edit:</p>
  
  <p>Based on the responses below, I am now working with:
  <a href="http://tips4java.wordpress.com/2008/11/06/wrap-layout/" rel="noreferrer">http://tips4java.wordpress.com/2008/11/06/wrap-layout/</a>  and
  <a href="http://code.google.com/p/verticalflowlayout/" rel="noreferrer">http://code.google.com/p/verticalflowlayout/</a></p>
  
  <p>I have the WrapLayout extending VerticalFlowLayout as such:</p>
  
  <pre><code>package LogicSim;
  
  import java.awt.*;
  import javax.swing.JScrollPane;
  import javax.swing.SwingUtilities;
  
  /**
   *  FlowLayout subclass that fully supports wrapping of components.
   */
  public class VerticalWrapLayout extends VerticalFlowLayout
  {
  private Dimension preferredLayoutSize;
  
  /**
  * Constructs a new &lt;code&gt;WrapLayout&lt;/code&gt; with a left
  * alignment and a default 5-unit horizontal and vertical gap.
  */
  public VerticalWrapLayout()
  {
      super();
  }
  
  /**
  * Constructs a new &lt;code&gt;FlowLayout&lt;/code&gt; with the specified
  * alignment and a default 5-unit horizontal and vertical gap.
  * The value of the alignment argument must be one of
  * &lt;code&gt;WrapLayout&lt;/code&gt;, &lt;code&gt;WrapLayout&lt;/code&gt;,
  * or &lt;code&gt;WrapLayout&lt;/code&gt;.
  * @param align the alignment value
  */
  public VerticalWrapLayout(int align)
  {
      super(align);
  }
  
  /**
  * Creates a new flow layout manager with the indicated alignment
  * and the indicated horizontal and vertical gaps.
  * &lt;p&gt;
  * The value of the alignment argument must be one of
  * &lt;code&gt;WrapLayout&lt;/code&gt;, &lt;code&gt;WrapLayout&lt;/code&gt;,
  * or &lt;code&gt;WrapLayout&lt;/code&gt;.
  * @param align the alignment value
  * @param hgap the horizontal gap between components
  * @param vgap the vertical gap between components
  */
  public VerticalWrapLayout(int align, int hgap, int vgap)
  {
      super(align, hgap, vgap);
  }
  
  /**
  * Returns the preferred dimensions for this layout given the
  * &lt;i&gt;visible&lt;/i&gt; components in the specified target container.
  * @param target the component which needs to be laid out
  * @return the preferred dimensions to lay out the
  * subcomponents of the specified container
  */
  @Override
  public Dimension preferredLayoutSize(Container target)
  {
      return layoutSize(target, true);
  }
  
  /**
  * Returns the minimum dimensions needed to layout the &lt;i&gt;visible&lt;/i&gt;
  * components contained in the specified target container.
  * @param target the component which needs to be laid out
  * @return the minimum dimensions to lay out the
  * subcomponents of the specified container
  */
  @Override
  public Dimension minimumLayoutSize(Container target)
  {
      Dimension minimum = layoutSize(target, false);
      minimum.width -= (getHgap() + 1);
      return minimum;
  }
  
  /**
  * Returns the minimum or preferred dimension needed to layout the target
  * container.
  *
  * @param target target to get layout size for
  * @param preferred should preferred size be calculated
  * @return the dimension to layout the target container
  */
  private Dimension layoutSize(Container target, boolean preferred)
  {
          synchronized (target.getTreeLock())
          {
      //  Each row must fit with the width allocated to the containter.
      //  When the container width = 0, the preferred width of the container
      //  has not yet been calculated so lets ask for the maximum.
  
      int targetWidth = target.getSize().width;
  
      if (targetWidth == 0)
          targetWidth = Integer.MAX_VALUE;
  
      int hgap = getHgap();
      int vgap = getVgap();
      Insets insets = target.getInsets();
      int horizontalInsetsAndGap = insets.left + insets.right + (hgap * 2);
      int maxWidth = targetWidth - horizontalInsetsAndGap;
  
      //  Fit components into the allowed width
  
      Dimension dim = new Dimension(0, 0);
      int rowWidth = 0;
      int rowHeight = 0;
  
      int nmembers = target.getComponentCount();
  
      for (int i = 0; i &lt; nmembers; i++)
      {
          Component m = target.getComponent(i);
  
          if (m.isVisible())
          {
              Dimension d = preferred ? m.getPreferredSize() : m.getMinimumSize();
  
              //  Can't add the component to current row. Start a new row.
  
              if (rowWidth + d.width &gt; maxWidth)
              {
                  addRow(dim, rowWidth, rowHeight);
                  rowWidth = 0;
                  rowHeight = 0;
              }
  
              //  Add a horizontal gap for all components after the first
  
              if (rowWidth != 0)
              {
                  rowWidth += hgap;
              }
  
              rowWidth += d.width;
              rowHeight = Math.max(rowHeight, d.height);
          }
      }
  
      addRow(dim, rowWidth, rowHeight);
  
      dim.width += horizontalInsetsAndGap;
      dim.height += insets.top + insets.bottom + vgap * 2;
  
      //  When using a scroll pane or the DecoratedLookAndFeel we need to
      //  make sure the preferred size is less than the size of the
      //  target containter so shrinking the container size works
      //  correctly. Removing the horizontal gap is an easy way to do this.
  
      Container scrollPane = SwingUtilities.getAncestorOfClass(JScrollPane.class, target);
  
      if (scrollPane != null)
      {
          dim.width -= (hgap + 1);
      }
  
      return dim;
  }
  }
  
  /*
   *  A new row has been completed. Use the dimensions of this row
   *  to update the preferred size for the container.
   *
   *  @param dim update the width and height when appropriate
   *  @param rowWidth the width of the row to add
   *  @param rowHeight the height of the row to add
   */
  private void addRow(Dimension dim, int rowWidth, int rowHeight)
  {
      dim.width = Math.max(dim.width, rowWidth);
  
      if (dim.height &gt; 0)
      {
          dim.height += getVgap();
      }
  
      dim.height += rowHeight;
  }
  }
  </code></pre>
  
  <p>Here is my frame setup:</p>
  
  <pre><code>    JFrame frame = new JFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setSize(300, 300);
      frame.setVisible(true);
  
  
      JPanel panel = new JPanel();
      panel.setLayout( new VerticalWrapLayout(0) );
  
      JScrollPane pane = new JScrollPane(panel);
      frame.add( pane, BorderLayout.CENTER );
  
      for (int i=0; i &lt; 80; i++ ) {
          panel.add( new JLabel( "Label" + i ) );
      }
  </code></pre>
  
  <p>Now, this sets up the labels in vertical columns in the way that I'm after, but it still creates the vertical scroll bar.  I'm pretty shaky when it comes to modifying the VerticalWrapLayout class.  Also, I really don't understand how the JScrollPane interacts will these classes.  Any suggestions on how to proceed?</p>
  
  <hr>
  
  <p><strong>Solved!</strong>  Please see the answers below as well as my answer.</p>