added AlignLayout demo

java/5-layout/DemoAlignLayout.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 DemoAlignLayout extends JFrame {
+
+	public static void main(String[] args) {
+		DemoAlignLayout demo = new DemoAlignLayout();
+	}
+
+	DemoAlignLayout() {
+		
+		this.setSize(800, 300);
+		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+
+		// layout 
+		this.setLayout(new AlignLayout(40, 40));
+
+		// add components
+		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);
+
+		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);
+
+		System.out.println("Preferred size: " + this.getPreferredSize());
+		System.out.println("Minimum size: " + this.getMinimumSize());
+
+		this.setVisible(true);		
+	}
+
+	// I made this to make it easy to add some debug information
+	void debugBorder(JComponent c) {
+		// try uncommenting this
+		c.setBorder(BorderFactory.createLineBorder(Color.black));
+	}
+}
+
+
+
+/**
+ * A layout manager that arranges components in a horizontal line equally spaced 
+ * and centred vertically in the parent container.
+ */
+class AlignLayout implements LayoutManager {
+
+	int minimumSpacing;
+	int preferredSpacing;
+
+	/** Construct a new AlignLayout object with spacing between components. */
+	public AlignLayout(int minSpacing, int preferredSpacing) {
+		super();
+		this.minimumSpacing = minimumSpacing;
+		this.preferredSpacing = preferredSpacing;
+	}
+
+	// for specialized layouts, not used here
+	public void addLayoutComponent(String name, Component comp) { }
+	public void removeLayoutComponent(Component comp) {	}
+
+	/**
+	 * Calculates the preferred size dimensions for the specified panel given
+	 * the components in the specified parent container.
+	 */
+	public Dimension preferredLayoutSize(Container parent) {
+
+		synchronized (parent.getTreeLock()) {
+
+			// get space needed for all children
+			Dimension space = calculateSpace(parent, true);
+
+			// this container's padding
+			Insets insets = parent.getInsets();
+
+			Dimension d = new Dimension(insets.left + space.width +insets.right, 
+										insets.top + space.height + insets.bottom);
+			return d;
+		}
+	}
+
+
+	/**
+	 * Calculates the minimum size dimensions for the specified panel given the
+	 * components in the specified parent container.
+	 */
+	public Dimension minimumLayoutSize(Container parent) {
+
+		synchronized (parent.getTreeLock()) {
+
+			// get space needed for all children
+			Dimension space = calculateSpace(parent, false);
+
+			// this container's padding
+			Insets insets = parent.getInsets();
+
+			Dimension d = new Dimension(insets.left + space.width +insets.right, 
+										insets.top + space.height + insets.bottom);
+			return d;
+		}
+	}
+
+
+	/**
+	 * Lays out the container in the specified panel.
+	 */
+	public void layoutContainer(Container parent) {
+
+		synchronized (parent.getTreeLock()) {
+
+			// get space needed for all children (preferred)
+			Dimension space = calculateSpace(parent, true);
+
+			// this container's padding
+			Insets insets = parent.getInsets();
+
+			// get actual space available in parent
+			int w = parent.getWidth() - insets.left - insets.right;
+			int h = parent.getHeight() - insets.top - insets.bottom;
+
+			System.out.println("layoutContainer (parent size " + w + "," + h + ")");
+
+			// vertical centre line to layout component
+			int y = h / 2;
+
+			// starting x is left side of all components to lay out
+			int x = (w - space.width) / 2;
+
+			int nComponents = parent.getComponentCount();
+			for (int i = 0; i < nComponents; i++) {
+
+				Component c = parent.getComponent(i);
+
+				Dimension d = c.getPreferredSize();
+
+				c.setBounds(x, y - d.height / 2, d.width, d.height);
+
+				x += d.width + preferredSpacing;
+			}
+
+		}
+	}	
+
+
+	/*
+	 * Precondition: the caller has gotten the treelock.
+	 */
+	private Dimension calculateSpace(Container parent, boolean isPreferred) {
+
+		// find total width for all components and
+		// height of tallest component
+		Dimension result = new Dimension(0,0);
+
+		int nComponents = parent.getComponentCount();
+		for (int i = 0; i < nComponents; i++) {
+
+			Dimension d;
+			if (isPreferred) {
+				d = parent.getComponent(i).getPreferredSize();
+			} else {
+				d = parent.getComponent(i).getMinimumSize();
+			}
+			// update the total width and height required
+			result.width += d.width;
+			result.height = Math.max(result.height, d.height);
+		}
+
+		// add spacing in between components
+		if (isPreferred) {
+			result.width += (nComponents - 1) * preferredSpacing;
+		} else {
+			result.width += (nComponents - 1) * minimumSpacing;
+		}		
+
+		return result;
+	}
+
+
+
+
+
+}
+
+
+
+
+