PICalculator.java Source code

Introduction

Here is the source code for PICalculator.java

Source

/******************************************************************************
 * Copyright (c) 1998, 2004 Jackwind Li Guojie
 * All right reserved. 
 * 
 * Created on Oct 25, 2003 4:12:32 PM by JACK
 * $Id: PICalculator.java,v 1.1 2003/12/22 12:07:54 jackwind Exp $
 * 
 * visit: http://www.asprise.com/swt
 *****************************************************************************/

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.SelectionEvent;
import org.eclipse.swt.events.SelectionListener;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

/**
 * Illustrates multithread UI programming issues.
 */
public class PICalculator {
    Display display = new Display();
    Shell shell = new Shell(display);
    Button buttonThread = new Button(shell, SWT.PUSH);
    Button buttonAsyncExec = new Button(shell, SWT.PUSH);

    public PICalculator(boolean asyncExecEnabled) {
        final boolean async = asyncExecEnabled;

        shell.setText("PI Calculator");
        shell.setSize(400, 80);

        Rectangle clientArea = shell.getClientArea();

        buttonThread.setText("Click here to calculate PI  [Non-UI thread UI Update]");
        buttonThread.setBounds(clientArea.x, clientArea.y, clientArea.width, clientArea.height / 2);
        buttonThread.addSelectionListener(new SelectionListener() {
            public void widgetDefaultSelected(SelectionEvent e) {
            }

            public void widgetSelected(SelectionEvent e) {
                buttonThread.setText("Calculation in progress ...");
                getTask(buttonThread).start();
            }
        });

        buttonAsyncExec.setText("Click here to calculate PI  [asynExec method UI Update]");
        buttonAsyncExec.setBounds(clientArea.x, clientArea.y + clientArea.height / 2, clientArea.width,
                clientArea.height / 2);
        buttonAsyncExec.addSelectionListener(new SelectionListener() {
            public void widgetDefaultSelected(SelectionEvent e) {
            }

            public void widgetSelected(SelectionEvent e) {
                buttonAsyncExec.setText("Calculation in progress ...");
                getTask2(buttonAsyncExec).start();
            }
        });
        shell.open();

        while (!shell.isDisposed()) {
            if (!display.readAndDispatch()) {
                display.sleep();
            }
        }

        display.dispose();
    }

    public static void main(String[] args) {
        // new CalculatePI(false);
        new PICalculator(true);
    }

    public Thread getTask(Button button) {
        final Button theButton = button;
        return new Thread() {
            public void run() {
                double pi = calculatePI(9999999);
                theButton.setText("PI = " + pi); // Update UI.
            }
        };
    }

    public Thread getTask2(Button button) {
        final Button theButton = button;
        return new Thread() {

            public void run() {
                final double pi = calculatePI(9999999);

                display.asyncExec(new Runnable() {
                    public void run() {

                        // Update UI.

                        theButton.setText("PI = " + pi);

                    }
                });
            }
        };
    }

    /**
     * Calculate value of PI using Vieta's formula. For a complete discussion,
     * please visit:
     * http://documents.wolfram.com/v4/GettingStarted/CalculatingPi.html
     * 
     * @param nestedLevel -
     *            level of nested square roots in Vieta's formula.
     * @return value of PI
     */
    public static double calculatePI(int nestedLevel) {
        double product = 1;
        double lastSqrtValue = 0;

        for (int i = 0; i < nestedLevel; i++) {
            double sqrt = getNextSqrtValue(lastSqrtValue);
            product *= 0.5 * sqrt;

            lastSqrtValue = sqrt;
        }

        return 2 / product;
    }

    /**
     * Return the square root item value.
     * 
     * @param lastValue -
     *            last square root item value.
     * @return
     */
    public static double getNextSqrtValue(double lastValue) {
        return Math.sqrt(2 + lastValue);
    }
}