Question

In short, I want to achieve this layout using swing:

Notice two main objectives:

• JPanels behaves as text, they are wrapped to width of a window,
  and in case of lack of space, they are wraped to next “lines” of
  JPanels.

• There is no horizontal scorll, but vertical scroll is present to
  privide access to view all possible elements in window.

Nick Rippe provided an almost done solution below, it can be seen here as standalone java program with my updated more-random innermost textarea strings and left aligment.

The last step is to fix each-row top alignment of textareas in CPanel:

((WrapLayout)getLayout()).setAlignOnBaseline( true );

Complete solution:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.Border;

public class APanel extends JScrollPane {

    int width = 0;

    public static String getRandomMultilineText() {
        String filler = "";
        int words = (int) (Math.random() * 7) + 1;
        for ( int w = 0 ; w < words ; w++ ) {
            int lettersInWord = (int) (Math.random() * 12) + 1;
            for ( int l = 0 ; l < lettersInWord ; l++ ) {
                filler += "a";
            }
            filler += "\n";
        }
        return filler.trim();
    }

    public APanel() {
        super();

        setAlignmentX( LEFT_ALIGNMENT );
        setAlignmentY( TOP_ALIGNMENT );

        final Box B = Box.createVerticalBox();
        B.setAlignmentX( LEFT_ALIGNMENT );
        B.setAlignmentY( TOP_ALIGNMENT );

        for ( int i = 0 ; i < 4 ; i++ ) {
            B.add( new CPanel() {


                //Important!!! Make sure the width always fits the screen
                public Dimension getPreferredSize() {


                    Dimension result = super.getPreferredSize();
                    result.width = width - 20; // 20 is for the scroll bar width
                    return result;
                }
            } );
        }

        setViewportView( B );

        //Important!!! Need to invalidate the Scroll pane, othewise it
        //doesn't try to lay out when the container is shrunk
        addComponentListener( new ComponentAdapter() {
            public void componentResized( ComponentEvent ce ) {
                width = getWidth();
                B.invalidate();
            }
        } );
    }

    // nothing really very special in this class - mostly here for demonstration
    public static class CPanel extends JPanel {

        public CPanel() {
            super( new WrapLayout( WrapLayout.LEFT ) );
            ((WrapLayout)getLayout()).setAlignOnBaseline( true);


            setOpaque( true );
            setBackground( Color.gray );
            setAlignmentY( TOP_ALIGNMENT );
            setAlignmentX( LEFT_ALIGNMENT );


            int wordGroups = (int) (Math.random() * 14) + 7;

            //Adding test data (TextAreas)
            for ( int i = 0 ; i < wordGroups ; i++ ) {

                JTextArea ta = new JTextArea( getRandomMultilineText() );
                ta.setAlignmentY( TOP_ALIGNMENT );
                ta.setAlignmentX( LEFT_ALIGNMENT);
                add( ta );
            }
            Border bx = BorderFactory.createTitledBorder( "Lovely container" );

            setBorder( bx );
        }
    }

    public static void main( String[] args ) {
        final JFrame frame = new JFrame();
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.add( new APanel() );
        frame.pack();
        frame.setSize( 400 , 300 );
        frame.setLocationRelativeTo( null );
        frame.setVisible( true );
    }
}

Answer 1

Your problem is your calculation of your preferredSize of panel C. This preferred size needs to both be overridden (for the width) and contain the default height.

I’ve put together a demonstration so you can see how this would be done:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class APanel extends JScrollPane {

    int width = 0;

    public APanel(){
        super();        

        final Box B = Box.createVerticalBox();

        for(int i = 0; i < 4; i++){
            B.add(new CPanel(){

                //Important!!! Make sure the width always fits the screen
                public Dimension getPreferredSize(){
                    Dimension result = super.getPreferredSize();
                    result.width = width - 20; // 20 is for the scroll bar width
                    return result;
                }

            });
        }

        setViewportView(B);

        //Important!!! Need to invalidate the Scroll pane, othewise it
        //doesn't try to lay out when the container is shrunk
        addComponentListener(new ComponentAdapter(){
            public void componentResized(ComponentEvent ce){
                width = getWidth();
                B.invalidate();
            }
        });
    }

    // nothing really very special in this class - mostly here for demonstration
    public static class CPanel extends JPanel{

        //Test Data - not necessary
        static StringBuffer fillerString;
        static {
            fillerString = new StringBuffer();
            int i = 0;
            for(char c = '0'; c < 'z'; c++){
                fillerString.append(c);
                if(i++ %10 == 0){
                    fillerString.append('\n');
                }
            }
        }

        public CPanel(){
            super(new WrapLayout());
            setOpaque(true);
            setBackground(Color.gray);

            //Adding test data (TextAreas)
            for(int i = 0; i < 9; i++){
                JTextArea ta = new JTextArea(fillerString.toString());
                ta.setAlignmentX(LEFT_ALIGNMENT);
                add(ta);
            }

            setBorder(BorderFactory.createTitledBorder("Lovely container"));
        }
    }

    public static void main(String[] args){
        final JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new APanel());
        frame.pack();
        frame.setSize(400, 300);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

}