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The following example is an advancement of the above example. This example shows how to handle exceptions. For example, the following code catches the NumberFormatException in case leaves either of the text boxes empty or enters an invalid value such as a String.

/* =========================================================== File Name : RunTimeExcepApp.java WebSite : http://javaproglang.blogspot.in/ Facebook : https://www.facebook.com/AdvanceJavaProgramming Twitter ID : https://twitter.com/AdvanceJava Created By : Bintu Chaudhary =========================================================== */ import javax.swing.*; import java.awt.event.*; import java.awt.*; public class RunTimeExcepApp extends JApplet implements ActionListener { String ansStr, strFirst, strSecond; JLabel lblFirst,lblSecond,lblAns; JTextField txtFirst,txtSecond; Container contPane; public void init() { contPane = getContentPane( ); contPane.setLayout(null); lblAns = new JLabel (); lblFirst = new JLabel ("Enter the first number:"); txtFirst = new JTextField ( ); lblSecond = new JLabel ("Enter the second number:"); txtSecond = new JTextField ( ); lblFirst.setBounds(75,15,175,25); txtFirst.setBounds(230,15,100,25); lblSecond.setBounds(75,70,175,25); txtSecond.setBounds(230,70,100,25); lblAns.setBounds(120,150,500,40); contPane.add(lblFirst); contPane.add(txtFirst); contPane.add(lblSecond); contPane.add(txtSecond); contPane.add(lblAns); Font font = new Font("TimesRoman", Font.PLAIN, 24); lblAns.setFont(font); txtFirst.addActionListener(this); txtSecond.addActionListener(this); } public void actionPerformed (ActionEvent actEvt) { try { strFirst = txtFirst.getText(); strSecond = txtSecond.getText(); int intFirst = Integer.parseInt(strFirst); int intSecond = Integer.parseInt(strSecond); int answer = intFirst / intSecond; ansStr = String.valueOf(answer); lblAns.setText("The answer is :" + ansStr); } catch(NumberFormatException numFmtExcep) { lblAns.setText("Invalid Number"); } } }

<HTML> <HEAD> <TITLE> This is an Applet Test </TITLE> </HEAD> <BODY> <APPLET Code="RunTimeExcepApp.class" Width=500 Height=300> </APPLET> </BODY> </HTML>

C:\>jdk1.4\bin>javac RunTimeExcepApp.java
C:\>jdk1.4\bin>appletviewer RunTimeExcepApp.html

The actionPerformed() uses the try and the catch blocks to handle the NumberFormatException. The below Diagram shows what happens when the user leaves the text fields blank or enters an invalid numerical value. When the program gets to the first call to String.valueOf(). Java generates the NumberFormatException exception, which causes program execution to jump to the catch block. In the catch block, the program sets the display string to "Invalid Number". This is done by setting the text of the label to "Invalid Number".

Invalid numerical value being entered

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Java Exception Handling

Catching Java Exceptions	Catching a RunTime Exception
Handling Multiple Exceptions	The finally Clause
Creating User-defined Exceptions

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Catching a RunTime Exception

Java Exception Handling

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