I have a panel(JPanel) and it has FlowLayout by default. It has no preferredsize. I have a JScrollPane. So When I am adding buttons to the panel, the buttons are horizontally added. I want that to be added vertically.

panel = new JPanel();
JButton clearButton = new JButton("CLEAR");
panel.add(button);
JScrollPane scroller = new JScrollPane(panel);
scroller.setWheelScrollingEnabled(true);
scroller.setPreferredSize(new Dimension(100, 80));
scroller.setMinimumSize(new Dimension(100, 80));
scroller.setMaximumSize(new Dimension(100, 80));
content.add(scroller, BorderLayout.WEST);

content is the container of the JFrame.

Now if I set a BoxLayout for the panel, then the buttons are left-aligned and I don't want that. So I can't add this code : panel.setLayout(new BoxLayout(panel,BoxLayout.Y_AXIS));

So can you tell me a process where I can add buttons vertically and also center aligned and after the area is full, then a vertical scrollbar will automatically come.

Okay, I have got some code from internet that modifies the FlowLayout and serves my purpose. But can anyone explain this to me :

import java.awt.*;

/**
  * A modified version of FlowLayout that allows containers using this
  * Layout to behave in a reasonable manner when placed inside a
  * JScrollPane
 * Class got from Internet, not written by me
  */
 public class ModifiedFlowLayout extends FlowLayout {
       public ModifiedFlowLayout() {
              super();
           }

           public ModifiedFlowLayout(int align) {
              super(align);
           }
       public ModifiedFlowLayout(int align, int hgap, int vgap) {
          super(align, hgap, vgap);
       }

    @Override
       public Dimension minimumLayoutSize(Container target) {
          // Size of largest component, so we can resize it in
          // either direction with something like a split-pane.
          return computeMinSize(target);
       }

    @Override
       public Dimension preferredLayoutSize(Container target) {
          return computeSize(target);
       }

       private Dimension computeSize(Container target) {
          synchronized (target.getTreeLock()) {
             int hgap = getHgap();
             int vgap = getVgap();
             int w = target.getWidth();

             // Let this behave like a regular FlowLayout (single row)
             // if the container hasn't been assigned any size yet
             if (w == 0) {
                w = Integer.MAX_VALUE;
             }

             Insets insets = target.getInsets();
             if (insets == null){
                insets = new Insets(0, 0, 0, 0);
             }
             int reqdWidth = 0;

             int maxwidth = w - (insets.left + insets.right + hgap * 2);
             int n = target.getComponentCount();
             int x = 0;
             int y = insets.top + vgap; // FlowLayout starts by adding vgap, so do that here too.
             int rowHeight = 0;

             for (int i = 0; i < n; i++) {
                Component c = target.getComponent(i);
                if (c.isVisible()) {
                   Dimension d = c.getPreferredSize();
                   if ((x == 0) || ((x + d.width) <= maxwidth)) {
                      // fits in current row.
                      if (x > 0) {
                         x += hgap;
                      }
                      x += d.width;
                      rowHeight = Math.max(rowHeight, d.height);
                   }
                   else {
                      // Start of new row
                      x = d.width;
                      y += vgap + rowHeight;
                      rowHeight = d.height;
                   }
                   reqdWidth = Math.max(reqdWidth, x);
                }
             }
             y += rowHeight;
             y += insets.bottom;
             return new Dimension(reqdWidth+insets.left+insets.right, y);
          }
       }

       private Dimension computeMinSize(Container target) {
          synchronized (target.getTreeLock()) {
             int minx = Integer.MAX_VALUE;
             int miny = Integer.MIN_VALUE;
             boolean found_one = false;
             int n = target.getComponentCount();

             for (int i = 0; i < n; i++) {
                Component c = target.getComponent(i);
                if (c.isVisible()) {
                   found_one = true;
                   Dimension d = c.getPreferredSize();
                   minx = Math.min(minx, d.width);
                   miny = Math.min(miny, d.height);
                }
             }
             if (found_one) {
                return new Dimension(minx, miny);
             }
             return new Dimension(0, 0);
          }
       }

    }

I will be greatful to the person.

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