Solution

HTML Interface to Applet

<APPLET CODEBASE="/applets/magelang/AWT-Training/classes/" CODE="RatioLayout.class" WIDTH= HEIGHT= ALIGN=CENTER></APPLET>

Java Code

import java.awt.*;
import java.util.Vector;
import java.util.StringTokenizer;

/* RatioLayout.java -- Layout manager for Java containers
 * 
 * This layout manager allows you to specify ratios of x,y,width,height
 * characteristics of the components.  For example,
 *
 * setLayout(new RatioLayout());
 * add("0,0;.45,.5", new Button("OK")); // upper left corner, 45% x 50%
 * add(".75,.75", new Button("QUIT"));  // 75%,75% and use preferred size
 *
 * You may also specify position coordinates as "c", implying "center".
 *
 * add("c,.2", new Button("OK")); // center across, 20% down 
 *
 * Terence Parr
 * MageLang Institute, www.MageLang.com
 */
public class RatioLayout implements LayoutManager {

    // track the ratios for each object of form "xratio,yratio;wratio,hratio"
    Vector ratios = new Vector(10);
    // track the components also so we can remove associated modifier
    // if necessary.
    Vector components = new Vector(10);

    public void addLayoutComponent(String r, Component comp) {
        ratios.addElement(r);
        components.addElement(comp);
    }

    public void removeLayoutComponent(Component comp) {
        int i = components.indexOf(comp);
        if ( i!=-1 ) {
            ratios.removeElementAt(i);
            components.removeElementAt(i);
        }
    }

    public Dimension preferredLayoutSize(Container target) {
        return target.size();
    }

    public Dimension minimumLayoutSize(Container target) {
        return target.size();
    }

    public void layoutContainer(Container target) {
        Insets insets = target.insets();
        int ncomponents = target.countComponents();
        Dimension d = target.size();
        d.width -=  insets.left+insets.right;
        d.height -= insets.top+insets.bottom;
        for (int i = 0 ; i < ncomponents ; i++) {
            Component comp = target.getComponent(i);
            Dimension compDim = comp.preferredSize();
            StringTokenizer st =
                new StringTokenizer((String)ratios.elementAt(i), ", \t;");
            float rx,ry;
            String sx = st.nextToken();
            String sy = st.nextToken();
            // Compute ratios for x,y.
            // If a coordinate is "c" then center the component.
            if ( sx.equalsIgnoreCase("c") ) {
                // compute: what is ratio position for left-edge
                // of component when centered?
                double px = (d.width/2.0) - (compDim.width/2.0);
                rx = (float)px/d.width;  // convert to ratio
            }
            else {
                rx = Float.valueOf(sx).floatValue();
            }
            if ( sy.equalsIgnoreCase("c") ) {
                double py = (d.height/2.0) - (compDim.height/2.0);
                ry = (float)py/d.height; // convert to ratio
            }
            else {
                ry = Float.valueOf(sy).floatValue();
            }
            float rw=0;
            float rh=0;
            int w,h;
            if ( st.hasMoreElements() ) {// get width, height if they exist
                rw = Float.valueOf(st.nextToken()).floatValue();
                rh = Float.valueOf(st.nextToken()).floatValue();
                w = (int)(d.width*rw);
                h = (int)(d.height*rh);
            }
            else {
                w = compDim.width;
                h = compDim.height;
            }
            int x = (int)(d.width*rx);
            int y = (int)(d.height*ry);
            comp.reshape(x+insets.left,y+insets.top,w,h);
        }
    }
    
    public String toString() {
        return getClass().getName();
    }
}