package threadbook.ch09;

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class BalanceLookup extends JPanel {

private JTextField acctTF;

private JTextField pinTF;

private JButton searchB;

private JButton cancelB;

private JLabel balanceL;

private volatile Thread lookupThread;

public BalanceLookup() {

buildGUI();

hookupEvents();

}

private void buildGUI() {

JLabel acctL = new JLabel("Account Number:");

JLabel pinL = new JLabel("PIN:");

acctTF = new JTextField(12);

pinTF = new JTextField(4);

JPanel dataEntryP = new JPanel();

dataEntryP.setLayout(new FlowLayout(FlowLayout.CENTER));

dataEntryP.add(acctL);

dataEntryP.add(acctTF);

dataEntryP.add(pinL);

dataEntryP.add(pinTF);

searchB = new JButton("Search");

cancelB = new JButton("Cancel Search");

cancelB.setEnabled(false);

JPanel innerButtonP = new JPanel();

innerButtonP.setLayout(new GridLayout(1, -1, 5, 5));

innerButtonP.add(searchB);

innerButtonP.add(cancelB);

JPanel buttonP = new JPanel();

buttonP.setLayout(new FlowLayout(FlowLayout.CENTER));

buttonP.add(innerButtonP);

JLabel balancePrefixL = new JLabel("Account Balance:");

balanceL = new JLabel("BALANCE UNKNOWN");

JPanel balanceP = new JPanel();

balanceP.setLayout(new FlowLayout(FlowLayout.CENTER));

balanceP.add(balancePrefixL);

balanceP.add(balanceL);

JPanel northP = new JPanel();

northP.setLayout(new GridLayout(-1, 1, 5, 5));

northP.add(dataEntryP);

northP.add(buttonP);

northP.add(balanceP);

setLayout(new BorderLayout());

add(northP, BorderLayout.NORTH);

}

private void hookupEvents() {

searchB.addActionListener(new ActionListener() {

public void actionPerformed(ActionEvent e) {

search();

}

});

cancelB.addActionListener(new ActionListener() {

public void actionPerformed(ActionEvent e) {

cancelSearch();

}

});

}

private void search() {

// better be called by event thread!

ensureEventThread();

searchB.setEnabled(false);

cancelB.setEnabled(true);

balanceL.setText("SEARCHING ...");

// get a snapshot of this info in case it changes

String acct = acctTF.getText();

String pin = pinTF.getText();

lookupAsync(acct, pin);

}

private void lookupAsync(String acct, String pin) {

// Called by event thread, but can be safely

// called by any thread.

final String acctNum = acct;

final String pinNum = pin;

Runnable lookupRun = new Runnable() {

public void run() {

String bal = lookupBalance(acctNum, pinNum);

setBalanceSafely(bal);

}

};

lookupThread = new Thread(lookupRun, "lookupThread");

lookupThread.start();

}

private String lookupBalance(String acct, String pin) {

// Called by lookupThread, but can be safely

// called by any thread.

try {

// Simulate a lengthy search that takes 5 seconds

// to communicate over the network.

Thread.sleep(5000);

// result "retrieved", return it

return "1,234.56";

} catch ( InterruptedException x ) {

return "SEARCH CANCELLED";

}

}

private void setBalanceSafely(String newBal) {

// Called by lookupThread, but can be safely

// called by any thread.

final String newBalance = newBal;

Runnable r = new Runnable() {

public void run() {

try {

setBalance(newBalance);

} catch ( Exception x ) {

x.printStackTrace();

}

}

};

SwingUtilities.invokeLater(r);

}

private void setBalance(String newBalance) {

// better be called by event thread!

ensureEventThread();

balanceL.setText(newBalance);

cancelB.setEnabled(false);

searchB.setEnabled(true);

}

private void cancelSearch() {

// better be called by event thread!

ensureEventThread();

cancelB.setEnabled(false); // prevent additional requests

if ( lookupThread != null ) {

lookupThread.interrupt();

}

}

private void ensureEventThread() {

// throws an exception if not invoked by the

// event thread.

if ( SwingUtilities.isEventDispatchThread() ) {

return;

}

throw new RuntimeException("only the event " +

"thread should invoke this method");

}

public static void main(String[] args) {

BalanceLookup bl = new BalanceLookup();

JFrame f = new JFrame("Balance Lookup");

f.addWindowListener(new WindowAdapter() {

public void windowClosing(WindowEvent e) {

System.exit(0);

}

});

f.setContentPane(bl);

f.setSize(400, 150);

f.setVisible(true);

}

}