Numbers on JButtons and set JButtons to Opaque

Question

Hi everyone:
please check for me why numbers(like 1 to 35) don't appears on JButtons, and why I setOpaque(true) to JButtons, it doesn't work. Thanks
// why I can not see the numbers (1 to 35) in JButtons ????????????
// and how can I operate setOpaque(true) to JButtons.
import javax.swing.*;
import java.awt.*;
import java.awt.GridLayout;
public class DrawCalendar extends JPanel{
     private static DrawCalendar dC;
     private static JButton jB1,jB2,jB3;
     private static Dimension dMS;
     private static GridLayout gL;
     private static Container c;
     // why I can not see the numbers (1 to 35) in JButtons ????????????
     public DrawCalendar(){
          JButton j= new JButton("1");
     gL=new GridLayout(5,7,4,4);
          setLayout(gL);
add(j);
add(new JButton("2"));
add(new JButton("3"));
add(new JButton("4"));
add(new JButton("5"));
add(new JButton("6"));
add(new JButton("7"));
add(new JButton("8"));
add(new JButton("9"));
add(new JButton("10"));
add(new JButton("11"));
add(new JButton("12"));
add(new JButton("12"));
add(new JButton("14"));
add(new JButton("15"));
add(new JButton("16"));
add(new JButton("17"));
add(new JButton("18"));
add(new JButton("19"));
add(new JButton("20"));
add(new JButton("21"));
add(new JButton("22"));
add(new JButton("23"));
add(new JButton("24"));
add(new JButton("25"));
add(new JButton("26"));
add(new JButton("27"));
add(new JButton("28"));
add(new JButton("29"));
add(new JButton("30"));
add(new JButton("31"));
add(new JButton("32"));
add(new JButton("33"));
add(new JButton("34"));
add(new JButton("35"));
import java.awt.*;
import java.awt.Color;
import javax.swing.*;
import javax.swing.JButton;
import javax.swing.JMenuBar;
public class TestMain extends JFrame{
private static JButton b1, b2, b3;
private static TestMain tM;
     private static JPanel jP;
private static Container c;
private static DrawCalendar dC;
     public static void main(String[] args){
     tM = new TestMain();
     addItems();
     tM.setVisible(true);
     public TestMain(){
     super(" Test");
     dC=new DrawCalendar();
     setSize(600,600);
//set up layoutManager
c=getContentPane();
c.setLayout ( new GraphPaperLayout(new Dimension (8,20)));
//set up three Button and one JPanel
b1=new JButton("1");
b1.setOpaque(true);
b2=new JButton("2");
b2.setOpaque(true);
b3=new JButton("3");
b3.setOpaque(true);
//add the munuBar, the Jpanel and three JButtons
public static void addItems(){
     c.add(b1, new Rectangle(5,0,1,1));
     c.add(b2, new Rectangle(6,0,1,1));
c.add(b3, new Rectangle(7,0,1,1));
     c.add(dC, new Rectangle(5,1,3,5));
import java.awt.*;
import java.util.Hashtable;
import java.io.*;
* The <code>GraphPaperLayout</code> class is a layout manager that
* lays out a container's components in a rectangular grid, similar
* to GridLayout. Unlike GridLayout, however, components can take
* up multiple rows and/or columns. The layout manager acts as a
* sheet of graph paper. When a component is added to the layout
* manager, the location and relative size of the component are
* simply supplied by the constraints as a Rectangle.
* <p><code><pre>
* import java.awt.*;
* import java.applet.Applet;
* public class ButtonGrid extends Applet {
* public void init() {
* setLayout(new GraphPaperLayout(new Dimension(5,5)));
* // Add a 1x1 Rect at (0,0)
* add(new Button("1"), new Rectangle(0,0,1,1));
* // Add a 2x1 Rect at (2,0)
* add(new Button("2"), new Rectangle(2,0,2,1));
* // Add a 1x2 Rect at (1,1)
* add(new Button("3"), new Rectangle(1,1,1,2));
* // Add a 2x2 Rect at (3,2)
* add(new Button("4"), new Rectangle(3,2,2,2));
* // Add a 1x1 Rect at (0,4)
* add(new Button("5"), new Rectangle(0,4,1,1));
* // Add a 1x2 Rect at (2,3)
* add(new Button("6"), new Rectangle(2,3,1,2));
* </pre></code>
* @author Michael Martak
* Updated by Judy Bowen, September 2002 to allow serialization
public class GraphPaperLayout implements LayoutManager2, Serializable{
int hgap; //horizontal gap
int vgap; //vertical gap
Dimension gridSize; //grid size in logical units (n x m)
Hashtable compTable; //constraints (Rectangles)
* Creates a graph paper layout with a default of a 1 x 1 graph, with no
* vertical or horizontal padding.
public GraphPaperLayout() {
this(new Dimension(1,1));
* Creates a graph paper layout with the given grid size, with no vertical
* or horizontal padding.
public GraphPaperLayout(Dimension gridSize) {
this(gridSize, 0, 0);
* Creates a graph paper layout with the given grid size and padding.
* @param gridSize size of the graph paper in logical units (n x m)
* @param hgap horizontal padding
* @param vgap vertical padding
public GraphPaperLayout(Dimension gridSize, int hgap, int vgap) {
if ((gridSize.width <= 0) || (gridSize.height <= 0)) {
throw new IllegalArgumentException(
"dimensions must be greater than zero");
this.gridSize = new Dimension(gridSize);
this.hgap = hgap;
this.vgap = vgap;
compTable = new Hashtable();
* @return the size of the graph paper in logical units (n x m)
public Dimension getGridSize() {
return new Dimension( gridSize );
* Set the size of the graph paper in logical units (n x m)
public void setGridSize( Dimension d ) {
setGridSize( d.width, d.height );
* Set the size of the graph paper in logical units (n x m)
public void setGridSize( int width, int height ) {
gridSize = new Dimension( width, height );
public void setConstraints(Component comp, Rectangle constraints) {
compTable.put(comp, new Rectangle(constraints));
* Adds the specified component with the specified name to
* the layout. This does nothing in GraphPaperLayout, since constraints
* are required.
public void addLayoutComponent(String name, Component comp) {
* Removes the specified component from the layout.
* @param comp the component to be removed
public void removeLayoutComponent(Component comp) {
compTable.remove(comp);
* Calculates the preferred size dimensions for the specified
* panel given the components in the specified parent container.
* @param parent the component to be laid out
* @see #minimumLayoutSize
public Dimension preferredLayoutSize(Container parent) {
return getLayoutSize(parent, true);
* Calculates the minimum size dimensions for the specified
* panel given the components in the specified parent container.
* @param parent the component to be laid out
* @see #preferredLayoutSize
public Dimension minimumLayoutSize(Container parent) {
return getLayoutSize(parent, false);
* Algorithm for calculating layout size (minimum or preferred).
* <p>
* The width of a graph paper layout is the largest cell width
* (calculated in <code>getLargestCellSize()</code> times the number of
* columns, plus the horizontal padding times the number of columns
* plus one, plus the left and right insets of the target container.
* <p>
* The height of a graph paper layout is the largest cell height
* (calculated in <code>getLargestCellSize()</code> times the number of
* rows, plus the vertical padding times the number of rows
* plus one, plus the top and bottom insets of the target container.
* @param parent the container in which to do the layout.
* @param isPreferred true for calculating preferred size, false for
* calculating minimum size.
* @return the dimensions to lay out the subcomponents of the specified
* container.
* @see java.awt.GraphPaperLayout#getLargestCellSize
protected Dimension getLayoutSize(Container parent, boolean isPreferred) {
Dimension largestSize = getLargestCellSize(parent, isPreferred);
Insets insets = parent.getInsets();
largestSize.width = ( largestSize.width * gridSize.width ) +
( hgap * ( gridSize.width + 1 ) ) + insets.left + insets.right;
largestSize.height = ( largestSize.height * gridSize.height ) +
( vgap * ( gridSize.height + 1 ) ) + insets.top + insets.bottom;
return largestSize;
* Algorithm for calculating the largest minimum or preferred cell size.
* <p>
* Largest cell size is calculated by getting the applicable size of each
* component and keeping the maximum value, dividing the component's width
* by the number of columns it is specified to occupy and dividing the
* component's height by the number of rows it is specified to occupy.
* @param parent the container in which to do the layout.
* @param isPreferred true for calculating preferred size, false for
* calculating minimum size.
* @return the largest cell size required.
protected Dimension getLargestCellSize(Container parent,
boolean isPreferred) {
int ncomponents = parent.getComponentCount();
Dimension maxCellSize = new Dimension(0,0);
for ( int i = 0; i < ncomponents; i++ ) {
Component c = parent.getComponent(i);
Rectangle rect = (Rectangle)compTable.get(c);
if ( c != null && rect != null ) {
Dimension componentSize;
if ( isPreferred ) {
componentSize = c.getPreferredSize();
} else {
componentSize = c.getMinimumSize();
// Note: rect dimensions are already asserted to be > 0 when the
// component is added with constraints
maxCellSize.width = Math.max(maxCellSize.width,
componentSize.width / rect.width);
maxCellSize.height = Math.max(maxCellSize.height,
componentSize.height / rect.height);
return maxCellSize;
* Lays out the container in the specified container.
* @param parent the component which needs to be laid out
public void layoutContainer(Container parent) {
synchronized (parent.getTreeLock()) {
Insets insets = parent.getInsets();
int ncomponents = parent.getComponentCount();
if (ncomponents == 0) {
return;
// Total parent dimensions
Dimension size = parent.getSize();
int totalW = size.width - (insets.left + insets.right);
int totalH = size.height - (insets.top + insets.bottom);
// Cell dimensions, including padding
int totalCellW = totalW / gridSize.width;
int totalCellH = totalH / gridSize.height;
// Cell dimensions, without padding
int cellW = (totalW - ( (gridSize.width + 1) * hgap) )
/ gridSize.width;
int cellH = (totalH - ( (gridSize.height + 1) * vgap) )
/ gridSize.height;
for ( int i = 0; i < ncomponents; i++ ) {
Component c = parent.getComponent(i);
Rectangle rect = (Rectangle)compTable.get(c);
if ( rect != null ) {
int x = insets.left + ( totalCellW * rect.x ) + hgap;
int y = insets.top + ( totalCellH * rect.y ) + vgap;
int w = ( cellW * rect.width ) - hgap;
int h = ( cellH * rect.height ) - vgap;
c.setBounds(x, y, w, h);
// LayoutManager2 /////////////////////////////////////////////////////////
* Adds the specified component to the layout, using the specified
* constraint object.
* @param comp the component to be added
* @param constraints where/how the component is added to the layout.
public void addLayoutComponent(Component comp, Object constraints) {
if (constraints instanceof Rectangle) {
Rectangle rect = (Rectangle)constraints;
if ( rect.width <= 0 || rect.height <= 0 ) {
throw new IllegalArgumentException(
"cannot add to layout: rectangle must have positive width and height");
if ( rect.x < 0 || rect.y < 0 ) {
throw new IllegalArgumentException(
"cannot add to layout: rectangle x and y must be >= 0");
setConstraints(comp, rect);
} else if (constraints != null) {
throw new IllegalArgumentException(
"cannot add to layout: constraint must be a Rectangle");
* Returns the maximum size of this component.
* @see java.awt.Component#getMinimumSize()
* @see java.awt.Component#getPreferredSize()
* @see LayoutManager
public Dimension maximumLayoutSize(Container target) {
return new Dimension(Integer.MAX_VALUE, Integer.MAX_VALUE);
* Returns the alignment along the x axis. This specifies how
* the component would like to be aligned relative to other
* components. The value should be a number between 0 and 1
* where 0 represents alignment along the origin, 1 is aligned
* the furthest away from the origin, 0.5 is centered, etc.
public float getLayoutAlignmentX(Container target) {
return 0.5f;
* Returns the alignment along the y axis. This specifies how
* the component would like to be aligned relative to other
* components. The value should be a number between 0 and 1
* where 0 represents alignment along the origin, 1 is aligned
* the furthest away from the origin, 0.5 is centered, etc.
public float getLayoutAlignmentY(Container target) {
return 0.5f;
* Invalidates the layout, indicating that if the layout manager
* has cached information it should be discarded.
public void invalidateLayout(Container target) {
// Do nothing

Answer 1

Hello,
I think you have really a problem with this layout.
Please first check the standard [url http://java.sun.com/docs/books/tutorial/uiswing/layout/using.html]LayoutManager.
JButtons are opaque usually and they will be shown if you use another LayoutManager:import java.awt.*;
import javax.swing.*;
class DrawCalendar extends JPanel
     private static DrawCalendar dC;
     private static JButton jB1, jB2, jB3;
     private static Dimension dMS;
     private static GridLayout gL;
     private static Container c;
     // why I can not see the numbers (1 to 35) in JButtons ????????????
     public DrawCalendar()
          JButton j = new JButton("1");
          gL = new GridLayout(5, 7, 4, 4);
          setLayout(gL);
          add(j);
          add(new JButton("2"));
          add(new JButton("3"));
          add(new JButton("4"));
          add(new JButton("5"));
          add(new JButton("6"));
          add(new JButton("7"));
          add(new JButton("8"));
          add(new JButton("9"));
          add(new JButton("10"));
          add(new JButton("11"));
          add(new JButton("12"));
          add(new JButton("12"));
          add(new JButton("14"));
          add(new JButton("15"));
          add(new JButton("16"));
          add(new JButton("17"));
          add(new JButton("18"));
          add(new JButton("19"));
          add(new JButton("20"));
          add(new JButton("21"));
          add(new JButton("22"));
          add(new JButton("23"));
          add(new JButton("24"));
          add(new JButton("25"));
          add(new JButton("26"));
          add(new JButton("27"));
          add(new JButton("28"));
          add(new JButton("29"));
          add(new JButton("30"));
          add(new JButton("31"));
          add(new JButton("32"));
          add(new JButton("33"));
          add(new JButton("34"));
          add(new JButton("35"));
public class TestMain extends JFrame
     private static JButton b1, b2, b3;
     private static TestMain tM;
     private static JPanel jP;
     private static Container c;
     private static DrawCalendar dC;
     public static void main(String[] args)
          tM = new TestMain();
          addItems();
          tM.setVisible(true);
     public TestMain()
          super(" Test");
          dC = new DrawCalendar();
          setSize(600, 600);
          //set up layoutManager
          c = getContentPane();
          c.setLayout(new FlowLayout());
          //set up three Button and one JPanel
          b1 = new JButton("1");
          b1.setOpaque(true);
          b2 = new JButton("2");
          b2.setOpaque(true);
          b3 = new JButton("3");
          b3.setOpaque(true);
     //add the munuBar, the Jpanel and three JButtons
     public static void addItems()
          c.add(b1);
          c.add(b2);
          c.add(b3);
          c.add(dC);
}regards
Tim