Java GUI โปรแกรมบวกเลข ที่ดัก Exception แล้ว

จากบทความ http://javacodeexam.blogspot.com/2014/03/java-gui.html

ตัวอย่างโค้ดในบทความ เรายังไม่ได้ดัก Exception ซึ่งจะทำให้เกิด Exception 

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: "asdf"

at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)

at java.lang.Double.parseDouble(Unknown Source)

at com.doesystem.JavaCodeExam.actionPerformed(JavaCodeExam.java:53)

at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)

at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)

at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)

at javax.swing.DefaultButtonModel.setPressed(Unknown Source)

at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)

at java.awt.Component.processMouseEvent(Unknown Source)

at javax.swing.JComponent.processMouseEvent(Unknown Source)

at java.awt.Component.processEvent(Unknown Source)

at java.awt.Container.processEvent(Unknown Source)

at java.awt.Component.dispatchEventImpl(Unknown Source)

at java.awt.Container.dispatchEventImpl(Unknown Source)

at java.awt.Component.dispatchEvent(Unknown Source)

at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)

at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)

at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)

at java.awt.Container.dispatchEventImpl(Unknown Source)

at java.awt.Window.dispatchEventImpl(Unknown Source)

at java.awt.Component.dispatchEvent(Unknown Source)

at java.awt.EventQueue.dispatchEventImpl(Unknown Source)

at java.awt.EventQueue.access$200(Unknown Source)

at java.awt.EventQueue$3.run(Unknown Source)

at java.awt.EventQueue$3.run(Unknown Source)

at java.security.AccessController.doPrivileged(Native Method)

at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)

at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)

at java.awt.EventQueue$4.run(Unknown Source)

at java.awt.EventQueue$4.run(Unknown Source)

at java.security.AccessController.doPrivileged(Native Method)

at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)

at java.awt.EventQueue.dispatchEvent(Unknown Source)

at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)

at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)

at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)

at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

at java.awt.EventDispatchThread.run(Unknown Source)

ดังนั้น ในตัวอย่างโค้ดนี้เรามาดูตัวอย่างโค้ดที่ได้ทำการดัก Exception กันคับ

ตัวอย่างโค้ด

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import javax.swing.JButton;

import javax.swing.JFrame;

import javax.swing.JLabel;

import javax.swing.JPanel;

import javax.swing.JTextField;

public class JavaCodeExam extends JFrame implements ActionListener {

private JFrame frame;

private JTextField txtField1;

private JTextField txtField2;

private JLabel lblAns;

public static void main(String[] args) throws Exception {

new JavaCodeExam();

}

public JavaCodeExam() {

this.frame = new JFrame();

this.frame.setVisible(true);

this.frame.setTitle("Frame By Java Code Exam");

this.frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

JPanel panel = new JPanel();

this.txtField1 = new JTextField(5);

this.txtField2 = new JTextField(5);

panel.add(this.txtField1);

panel.add(new JLabel(" + "));

panel.add(this.txtField2);

JButton btnAlert = new JButton("=");

btnAlert.addActionListener(this);

panel.add(btnAlert);

this.lblAns = new JLabel();

panel.add(this.lblAns);

this.frame.add(panel);

this.frame.pack();

this.frame.setSize(500, 200);

this.frame.setLocation(10, 10);

}

@Override

public void actionPerformed(ActionEvent e) {

try {

double val1 = Double.parseDouble(this.txtField1.getText());

double val2 = Double.parseDouble(this.txtField2.getText());

this.lblAns.setText((val1 + val2) + "");

} catch (NumberFormatException ex) {

ex.printStackTrace();

this.lblAns.setText("Cannot a Number");

} catch (Exception ex) {

ex.printStackTrace();

this.lblAns.setText(ex.getMessage());

}

}

}

ตัวอย่างนี้เราได้ทำการเพิ่ม try catch ให้กับโค้ด และดักจับ Exception โดยถ้าเกิด NumberFormatException ให้แสดงข้อความว่า Cannot a Number แต่ถ้าเกิด Exception อื่น ๆ จะแสดง message exception นั้น ๆ 

ใน catch เราได้ใส่ Exception ไว้ในตัวแปร ex และได้ทำการ printStackTrace เพื่อแสดงค่า Exceeption ใน Console

ผลลัพธ์ที่ได้