PercentLayout.java

package jas.util.layout;
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.LayoutManager2;
import java.util.Enumeration;
import java.util.Hashtable;

/**
 * Lays out components within a Container such that each component takes a fixed percentage of the size.
 * 
 * Each Component added to the Container must have a Constraint object that specifies what proportion 
 * of the container it will fill. The Component will be stretched to fill exactly that percentage.
 * 
 * @see Constraint
 */
public class PercentLayout implements LayoutManager2
{
	public void addLayoutComponent(Component component, Object constraint)
	{
		if (constraint instanceof Constraint)
		{
			hash.put(component,constraint);
		}
		else throw new IllegalArgumentException("Invalid constraint");
	}
	public void addLayoutComponent(String constraint, Component comp)
	{
		throw new IllegalArgumentException("Invalid constraint");
	}
	public void removeLayoutComponent(Component component)
	{
		hash.remove(component);
	}

	public Dimension preferredLayoutSize(Container p1)
	{
		int prefx=0;
		int prefy=0;
		
		Enumeration keys = hash.keys();
		while (keys.hasMoreElements())
		{
			Component comp = (Component) keys.nextElement();
			Constraint constraint = (Constraint) hash.get(comp);
			Dimension pref = comp.getPreferredSize();
			prefx += pref.width * 100/constraint.width; 
			prefy += pref.height * 100/constraint.height; 
		}
		int n = hash.size();
		return new Dimension(prefx/n,prefy/n);
	}
	public Dimension minimumLayoutSize(Container p1)
	{
		int minx=0;
		int miny=0;
		
		Enumeration keys = hash.keys();
		while (keys.hasMoreElements())
		{
			Component comp = (Component) keys.nextElement();
			Constraint constraint = (Constraint) hash.get(comp);
			Dimension min = comp.getMinimumSize();
			int mx = (int) (min.width * 100/constraint.width); 
			int my = (int) (min.height * 100/constraint.height); 
			if (mx>minx) minx=mx;
			if (my>miny) miny=my;
		}
		return new Dimension(minx,miny);
	}
	public Dimension maximumLayoutSize(Container p1)
	{
		int maxx=Integer.MAX_VALUE;
		int maxy=Integer.MAX_VALUE;
		
		Enumeration keys = hash.keys();
		while (keys.hasMoreElements())
		{
			Component comp = (Component) keys.nextElement();
			Constraint constraint = (Constraint) hash.get(comp);
			Dimension max = comp.getMaximumSize();
			int mx = max.width==Integer.MAX_VALUE ? max.width : (int) (max.width * 100/constraint.width); 
			int my = max.height==Integer.MAX_VALUE ? max.height : (int) (max.height * 100/constraint.height); 
			if (mx<maxx) maxx=mx;
			if (my<maxy) maxy=my;
		}
		return new Dimension(maxx,maxy);
	}
	public void layoutContainer(Container p1)
	{
		Dimension size = p1.getSize();
		Enumeration keys = hash.keys();
		while (keys.hasMoreElements())
		{
			Component comp = (Component) keys.nextElement();
			Constraint constraint = (Constraint) hash.get(comp);
			int x = (int) (size.width*constraint.x/100);
			int y = (int) (size.height*constraint.y/100);
			int width = (int) (size.width*constraint.width/100);
			int height = (int) (size.height*constraint.height/100);
			comp.setBounds(x,y,width,height);
		}
	}
	public void invalidateLayout(Container p1)
	{
	}
	public float getLayoutAlignmentY(Container p1)
	{
		return 0.5f;
	}
	public float getLayoutAlignmentX(Container p1)
	{
		return 0.5f;
	}

	private Hashtable hash = new Hashtable();
	
	public static class Constraint
	{
		/**
		 * Creates a Constraint Object. 
		 * @param x The X position of the top left corner of the component (0-100)
		 * @param y The Y position of the top left corner of the component (0-100)
		 * @param width The percentage width of the component (0-100)
		 * @param height The percentage height of the component (0-100)
		 */
		public Constraint(double x, double y, double width, double height)
		{
			this.x = x;
			this.y = y;
			this.width = width;
			this.height = height;
		}
		double x,y,width,height;
	}
}