layout demo code

java/5-layout/DemoFormLayout.java

+import java.awt.*;
+import javax.swing.*;
+
+import java.awt.LayoutManager;
+import java.awt.Insets;
+import java.util.ArrayList;
+import java.awt.Component;
+import java.awt.Container;
+import java.awt.Dimension;
+
+// give positions and sizes for all widgets
+public class DemoFormLayout extends JFrame {
+
+	public static void main(String[] args) {
+		DemoFormLayout demo = new DemoFormLayout();
+	}
+
+	DemoFormLayout() {
+		
+		this.setSize(400, 150);
+		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+
+		// layout 
+		this.setLayout(new FormLayout(10, 10));
+
+		// add first pair
+		JComponent c;
+		c = new JLabel("Number");
+		// try uncommenting this
+		// c.setPreferredSize(new Dimension(200, 50));
+		debugBorder(c); 
+		this.add(c);
+
+		c = new JSlider(0, 100, 50);
+		debugBorder(c);
+		this.add(c);
+
+		// add second pair
+		c = new JLabel("Choice");
+		debugBorder(c); 
+		this.add(c);
+
+		// create a radio button group
+		ButtonGroup radiobuttons = new ButtonGroup();
+		JPanel radioPanel = new JPanel(new GridLayout(1, 0));
+		for (String s: new String[] {"A", "B", "C"})
+		{
+			JRadioButton rb = new JRadioButton(s);
+			radiobuttons.add(rb);
+			radioPanel.add(rb);
+		}
+		debugBorder(radioPanel);
+		this.add(radioPanel);
+				
+		this.setVisible(true);		
+	}
+
+	void debugBorder(JComponent c) {
+		// try uncommenting this
+		// c.setBorder(BorderFactory.createLineBorder(Color.black));
+	}
+}
+
+
+
+/**
+ * A layout manager that arranges components in a double column. In most cases
+ * the left column will hold a label and the right column will hold a component
+ * the user can manipulate. Preferred component sizes are respected as much as
+ * possible. Components in the left column are right justified; components in
+ * the right column are left justified.
+ * 
+ * @author Byron Weber Becker
+ */
+class FormLayout implements LayoutManager {
+
+	private int hGap = 8;
+	private int vGap = 8;
+
+	/** Construct a new FormLayout object. */
+	public FormLayout() {
+		super();
+	}
+
+	/**
+	 * Construct a new FormLayout object.
+	 * 
+	 * @param hGap
+	 *            the number of hortizontal pixels between components
+	 * @param vGap
+	 *            the number of vertical pixels between components
+	 */
+	public FormLayout(int hGap, int vGap) {
+		super();
+		this.hGap = hGap;
+		this.vGap = vGap;
+	}
+
+	/**
+	 * Adds the specified component with the specified name to the layout.
+	 * 
+	 * @param name
+	 *            the component name
+	 * @param comp
+	 *            the component to be added
+	 */
+	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) {
+	}
+
+	/**
+	 * 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) {
+		synchronized (parent.getTreeLock()) {
+			ColDims cd = colDims(parent, true);
+
+			Insets insets = parent.getInsets();
+			Dimension d = new Dimension(cd.left + cd.right + insets.left
+					+ insets.right, cd.height + insets.top + insets.bottom);
+			return d;
+		}
+	}
+
+	/*
+	 * Precondition: the caller has gotten the treelock. preferred = true for
+	 * preferred sizes; false for minimum sizes
+	 */
+	private ColDims colDims(Container parent, boolean preferred) {
+
+		// ColDims: left col width, right col width, height of all rows
+		ColDims cd = new ColDims();
+
+		int nComponents = parent.getComponentCount();
+
+		// step through rows (every other component)
+		for (int i = 1; i < nComponents; i += 2) {
+
+			Component left = parent.getComponent(i - 1);
+			Component right = parent.getComponent(i);
+
+			Dimension dLeft;
+			Dimension dRight;
+
+			if (preferred) {
+				dLeft = left.getPreferredSize();
+				dRight = right.getPreferredSize();
+			} else {
+				dLeft = left.getMinimumSize();
+				dRight = right.getMinimumSize();
+			}
+			cd.left = (int) Math.max(cd.left, dLeft.width);
+			cd.right = (int) Math.max(cd.right, dRight.width);
+			cd.height += (int) Math.max(dLeft.height, dRight.height);
+			cd.height += this.vGap;
+		}
+
+		// edge case (odd number of components...)
+		if (nComponents % 2 == 1) { // get the last one on the left
+			Component left = parent.getComponent(nComponents - 1);
+
+			Dimension dLeft;
+			if (preferred) {
+				dLeft = left.getPreferredSize();
+			} else {
+				dLeft = left.getMinimumSize();
+			}
+			cd.left = (int) Math.max(cd.left, dLeft.width);
+			cd.height += dLeft.height + this.vGap;
+		}
+
+		cd.left += this.hGap / 2;
+		cd.right += this.hGap / 2;
+		return cd;
+	}
+
+	/**
+	 * 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) {
+		synchronized (parent.getTreeLock()) {
+			ColDims cd = colDims(parent, false);
+
+			Insets insets = parent.getInsets();
+			Dimension d = new Dimension(cd.left + cd.right + insets.left
+					+ insets.right, cd.height + insets.top + insets.bottom);
+			return d;
+		}
+	}
+
+	/**
+	 * Lays out the container in the specified panel.
+	 * 
+	 * @param parent
+	 *            the component which needs to be laid out
+	 */
+	public void layoutContainer(Container parent) {
+		Insets insets = parent.getInsets();
+
+		synchronized (parent.getTreeLock()) {
+			ColDims cd = this.colDims(parent, true);
+
+			int desiredWidth = cd.left + cd.right + insets.left + insets.right;
+			double widthScale = Math.min(1.0, parent.getWidth()
+					/ (double) desiredWidth);
+			double heightScale = Math.min(1.0, parent.getHeight()
+					/ (double) cd.height);
+
+			double scale = Math.min(widthScale, heightScale);
+
+			// System.out.println("FormLayout.layoutContainer: widthScale = " +
+			// widthScale + "; heightScale = " + heightScale);
+
+			int midPt = (int) (((cd.left + insets.left + this.hGap) / (double) (cd.left
+					+ cd.right + insets.left + insets.right + hGap)) * parent
+					.getWidth());
+			int top = insets.top + this.vGap;
+
+			int nComponents = parent.getComponentCount();
+			for (int i = 1; i < nComponents; i += 2) {
+				Component left = parent.getComponent(i - 1);
+				Component right = parent.getComponent(i);
+				Dimension lDim = left.getPreferredSize();
+				Dimension rDim = right.getPreferredSize();
+
+				int rowHeight = (int) (Math.max(lDim.height, rDim.height) * heightScale);
+
+				// scale left side, if necessary; then position
+				if (lDim.width > desiredWidth || lDim.height > rowHeight) {
+					lDim.width = (int) (lDim.width * scale);
+					lDim.height = (int) (lDim.height * scale);
+				}
+				left.setBounds((midPt - lDim.width - this.hGap / 2), top,
+						lDim.width, lDim.height);
+
+				// scale right side, if necessary; then position
+				if (rDim.width > desiredWidth || rDim.height > rowHeight) {
+					rDim.width = (int) (rDim.width * scale);
+					rDim.height = (int) (rDim.height * scale);
+				}
+				right.setBounds(midPt + this.hGap / 2, top, rDim.width,
+						rDim.height);
+				top = top + rowHeight + this.vGap;
+			}
+			if (nComponents % 2 == 1) { // odd number of components -- get the
+										// last one on the left
+				Component left = parent.getComponent(nComponents - 1);
+				Dimension lDim = left.getPreferredSize();
+				lDim.width = (int) (lDim.width * scale);
+				lDim.height = (int) (lDim.height * scale);
+				left.setBounds((midPt - lDim.width - this.hGap / 2), top,
+						lDim.width, lDim.height);
+			}
+		}
+	}
+
+	private static class ColDims {
+		int left = 0;
+		int right = 0;
+		int height = 0;
+	}
+}
+
+
+
+
+

java/5-layout/LayoutDemo.java

+
+import java.awt.BorderLayout;
+import java.awt.Color;
+import java.awt.Component;
+import java.awt.Container;
+import java.awt.Dimension;
+import java.awt.FlowLayout;
+import java.awt.GridBagConstraints;
+import java.awt.GridBagLayout;
+import java.awt.GridLayout;
+import javax.swing.SpringLayout;
+import java.awt.LayoutManager;
+
+import javax.swing.Box;
+import javax.swing.BoxLayout;
+import javax.swing.JButton;
+import javax.swing.JCheckBox;
+import javax.swing.JFrame;
+import javax.swing.JLabel;
+import javax.swing.JPanel;
+import javax.swing.JTextArea;
+import javax.swing.JTextField;
+
+/* Demonstrate various layout managers available in Java, 
+ * including defining your own layout manager.
+ * 
+ * @author Byron Weber Becker
+ */
+public class LayoutDemo {
+	public static void main(String[] args) {
+		// These are stacked bottom to top, so put the first one
+		// to be discussed last.
+		new LayoutFrame("RandomLayout", new DemoRandomLayout());
+		new LayoutFrame("SpringLayout", new DemoSpringLayout());
+		new LayoutFrame("GridBagLayout", new DemoGridBagLayout());
+		new LayoutFrame("BorderLayout", new DemoBorderLayout());
+		new LayoutFrame("BoxLayout3", new DemoBoxLayout3());
+		new LayoutFrame("BoxLayout2", new DemoBoxLayout2());
+		new LayoutFrame("BoxLayout1", new DemoBoxLayout1());
+		new LayoutFrame("GridLayout", new DemoGridLayout());
+		new LayoutFrame("FlowLayout", new DemoFlowLayout());
+		new LayoutFrame("NullLayout", new DemoNullLayout());
+	}
+}
+
+class LayoutFrame extends JFrame {
+	private static int xPos = 10;
+	private static int yPos = 10;
+	private static final int OFFSET = 50;
+
+	public LayoutFrame(String title, JPanel contents) {
+		super(title);
+		this.setContentPane(contents);
+		this.setSize(300, 130);
+		// set this to keep the JFrame from shrinking too small
+		//this.setMinimumSize(new Dimension(150,  100));
+		this.setLocation(xPos, yPos);
+		xPos += OFFSET;
+		yPos += OFFSET;
+		//this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+		this.setVisible(true);
+	}
+
+}
+
+
+// give positions and sizes for all widgets
+class DemoNullLayout extends JPanel {
+	public DemoNullLayout() {
+		super();
+		this.setBackground(Color.DARK_GRAY);
+		
+		this.setLayout(null);
+		JButton b1 = new JButton("Button1");
+		JButton b2 = new JButton("Button2");
+		b1.setBounds(10, 20, 150, 50); // x, y, width, height
+		b2.setBounds(40, 60, 100, 30);
+		this.add(b2);
+		this.add(b1);
+	}
+}
+
+
+class DemoFlowLayout extends JPanel {
+	public DemoFlowLayout() {
+		super();
+		this.setBackground(Color.DARK_GRAY);
+		// note also FlowLayout(int alignment, int horizontalSpace, int verticalSpace);
+		this.setLayout(new FlowLayout());
+		this.add(new JButton("  One  "));
+		this.add(new JTextField("  Two  ", 10));
+		this.add(new JButton("  Three  "));
+		this.add(new JButton("  Four  "));
+	}
+}
+
+class DemoGridLayout extends JPanel {
+	private JButton one = new JButton("One");
+	private JButton two = new JButton("Two");
+	private JButton three = new JButton("Three");
+	private JButton four = new JButton("Four");
+	private JButton five = new JButton("Five");
+	private JButton six = new JButton("Six");
+
+	public DemoGridLayout() {
+		super();
+		this.setBackground(Color.DARK_GRAY);
+
+		// Set the layout strategy to a grid with 2 rows and 3 columns.
+		GridLayout strategy = new GridLayout(2, 3);
+		this.setLayout(strategy);
+
+		// Add the components 
+		// (always added in left-to-right, top-to-bottom reading order )
+		this.add(this.one);
+		this.add(this.two);
+		this.add(this.three);
+		this.add(this.four);
+		this.add(this.five);
+		this.add(this.six);
+	}
+}
+
+
+
+class DemoBoxLayout1 extends JPanel {
+	// Default behaviour of BoxLayout
+	public DemoBoxLayout1() {
+		super();
+		this.setBackground(Color.DARK_GRAY);
+
+		// try BoxLayout.X_AXIS as well 
+		this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
+		this.add(new JButton("One"));
+		this.add(new JButton("Two"));
+		this.add(new JTextArea("TextArea"));
+		this.add(new JButton("Three"));
+	}
+}
+
+class DemoBoxLayout2 extends JPanel {
+	public DemoBoxLayout2() {
+		super();
+		this.setBackground(Color.DARK_GRAY);
+
+		JTextArea ta = new JTextArea("TextArea");
+		// Text areas have infinite maximum size by default, so BoxLayout will
+		// grow it to fill all available space unless we place a limit.
+		ta.setMaximumSize(new Dimension(200, 150));
+		// now add same as DemoBoxLayout1
+		this.setLayout(new BoxLayout(this, BoxLayout.X_AXIS));
+		this.add(new JButton("One"));
+		this.add(new JButton("Two"));
+		this.add(ta);
+		this.add(new JButton("Three"));
+	}
+}
+
+class DemoBoxLayout3 extends JPanel {
+	// Using rigid areas, struts and glue
+	public DemoBoxLayout3() {
+		super();
+		this.setBackground(Color.DARK_GRAY);
+
+		this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
+		this.add(new JButton("One"));
+		this.add(Box.createRigidArea(new Dimension(0,10)));
+		this.add(Box.createVerticalGlue());
+		this.add(new JButton("Two"));
+		this.add(Box.createVerticalStrut(10));
+		this.add(new JButton("Three"));
+	}
+}
+
+
+class DemoBorderLayout extends JPanel {
+	public DemoBorderLayout() {
+		super();
+		this.setBackground(Color.DARK_GRAY);
+
+		this.setLayout(new BorderLayout());
+		this.add(new JButton("North"), BorderLayout.NORTH);
+		this.add(new JButton("East"), BorderLayout.EAST);
+		this.add(new JButton("West"), BorderLayout.WEST);
+		
+		// Layouts can be nested ...
+		
+		// Box is an easy-to-create JPanel with a BoxLayout
+		Box b = Box.createHorizontalBox();
+		b.add(Box.createHorizontalGlue());
+		b.add(new JButton("Ok"));
+		b.add(Box.createHorizontalStrut(20));
+		b.add(new JButton("Cancel"));
+		
+		this.add(b, BorderLayout.SOUTH);
+		
+		// nesting a previous demo panel ...
+		this.add(new DemoBoxLayout1(), BorderLayout.CENTER);
+	}
+}
+
+
+
+class DemoGridBagLayout extends JPanel {
+	public DemoGridBagLayout() {
+		super();
+		this.setBackground(Color.DARK_GRAY);
+
+		this.setLayout(new GridBagLayout());
+		
+		// create a constraints object
+		GridBagConstraints gc = new GridBagConstraints();
+		// stretch the widget horizontally and vertically
+		gc.fill = GridBagConstraints.BOTH;
+		gc.gridwidth = 1; // 1 grid cell wide
+		gc.gridheight = 3; // 3 grid cells tall
+		gc.weightx = 0.5; // the proportion of space to give this column
+		gc.weighty = 0.5; // the proportion of space to give this row
+		this.add(new JButton("One"), gc);
+		
+		// modify gc for the next widget to be added
+		gc.fill = GridBagConstraints.VERTICAL;
+		gc.gridwidth = 1; 
+		gc.gridheight = 1;
+		gc.gridx = 1;
+		gc.gridy = 0;
+		gc.anchor = GridBagConstraints.WEST;
+		this.add(new JButton("Two"), gc);
+		gc.gridy = 1;
+		gc.anchor = GridBagConstraints.CENTER;
+		this.add(new JButton("Three"), gc);
+		gc.gridy = 2;
+		gc.anchor = GridBagConstraints.EAST;
+		this.add(new JButton("Four"), gc);
+		// add something spanning across the bottom
+		gc.fill = GridBagConstraints.HORIZONTAL;
+		gc.gridx = 0;
+		gc.gridy = 3;
+		gc.gridwidth = 2;
+		this.add(new JButton("Five"), gc);
+	}
+}
+
+class DemoSpringLayout extends JPanel {
+	private JButton b1 = new JButton("b1 - - - - ");
+	private JTextArea t1 = new JTextArea("t1");
+	private JButton b2 = new JButton("b2");
+
+	public DemoSpringLayout() {
+		super();
+		this.setBackground(Color.DARK_GRAY);
+
+		SpringLayout layout = new SpringLayout();
+		this.setLayout(layout);
+		
+		this.add(this.b1);
+		this.add(this.t1);
+		this.add(this.b2);
+
+		// Add constraints
+		// constrain west side of b1 to be 10 pixels from west side of the panel
+		layout.putConstraint(SpringLayout.WEST, b1, 10, 
+			SpringLayout.WEST, this);
+		// constrain north side of b1 to be 10 pixels from north side of the panel
+		layout.putConstraint(SpringLayout.NORTH, b1, 10, 
+			SpringLayout.NORTH, this);
+
+		// constrain b2 to stay 10 pixels from left of panel
+		layout.putConstraint(SpringLayout.WEST, b2, 10, 
+			SpringLayout.WEST, this);		
+		// constrain b2 to stay 10 pixels from bottom of panel
+		layout.putConstraint(SpringLayout.SOUTH, b2, -10, 
+			SpringLayout.SOUTH, this);
+		
+		layout.putConstraint(SpringLayout.EAST, b2, 0, 
+			SpringLayout.EAST, b1);
+		
+		// Let the textarea grow as large as requested
+		t1.setMaximumSize(new Dimension(Integer.MAX_VALUE, 
+			Integer.MAX_VALUE));
+
+		// constrain t1 to be east of the buttons and spread vertically to fill
+		// the entire height of the panel
+		layout.putConstraint(SpringLayout.WEST, t1, 10, 
+			SpringLayout.EAST, b2);
+		layout.putConstraint(SpringLayout.NORTH, t1, 10, 
+			SpringLayout.NORTH, this);
+		layout.putConstraint(SpringLayout.SOUTH, t1, -10, 
+			SpringLayout.SOUTH, this);
+		layout.putConstraint(SpringLayout.EAST, t1, -10, 
+			SpringLayout.EAST, this );
+	}
+}
+
+
+class DemoRandomLayout extends JPanel {
+	private JButton one = new JButton("One");
+	private JButton two = new JButton("Two");
+	private JButton three = new JButton("Three");
+	private JButton four = new JButton("Four");
+	private JButton five = new JButton("Five");
+	private JButton six = new JButton("Six");
+
+	public DemoRandomLayout() {
+		super();
+		this.setBackground(Color.DARK_GRAY);
+
+		this.setLayout(new RandomLayout());
+
+		// Add the components.
+		this.add(this.one);
+		this.add(this.two);
+		this.add(this.three);
+		this.add(this.four);
+		this.add(this.five);
+		this.add(this.six);
+	}
+}
+
+// a custom layout manager
+class RandomLayout implements LayoutManager {
+    public void addLayoutComponent(String name, Component comp) {
+        ; // no-op
+    }
+    public void layoutContainer(Container container) {