how do i handle number format exception in java?

StackOverflow https://stackoverflow.com/questions/22828417

Question

I am running a simple applet in my machine.Note that when executing applet "Number format exception" error occurs when the applet is trying to run. The below code is shown

import java.util.*;
import java.awt.*;
import java.applet.*;

<html>
<body>
<applet code="s09_03.class" width=400 height=400>
</applet>
</body>
</html>

public class s09_03 extends Applet
{
GregorianCalendar cal=new GregorianCalendar();
String s,s1,s2,s3,s4;
int a=0,b=0,c=0,d=0;
public void start(){s=getParameter("fg");
s1=getParameter("as");
s2=getParameter("as1");
s3=getParameter("as2");
s4=getParameter("as3");
a=Integer.parseInt(s1);
b=Integer.parseInt(s2);
c=Integer.parseInt(s3);
d=Integer.parseInt(s4);
}
public void init()
{
}
public void paint(Graphics g)
{
if(s.equals("red"))g.setColor(Color.red);g.drawRect(a,b,c,d);
g.drawString("Color = "+"",25,25);
g.drawString("Calendar is"+cal.DATE+"/"+cal.MONTH+"/"+cal.YEAR,34,36);
}
}

The command used are

javac s09_03.java
and
appletviewer s09_03.java

Terminal output:

  java.lang.NumberFormatException: null 
    at java.lang.Integer.parseInt(Integer.java:443)
    at java.lang.Integer.parseInt(Integer.java:514)
    at s09_03.start(s09_03.java:22)
    at sun.applet.AppletPanel.run(AppletPanel.java:477)
    at java.lang.Thread.run(Thread.java:701).

So my question is why this error occurs and when does it usually occur??Also suggest some necessary changes in code so that the code runs without any error.Note that the code is being run through linux...Thanks...

~

Was it helpful?

Solution

Take a look Try-Catch, NumberFormatException, nullPointerException

Use try catch to handle the Exception

Try this, because you got the value as null. so check the passing value should not be null 

        try
        {
        a = Integer.parseInt(s1 != null ? s1 : "0");
        b = Integer.parseInt(s2 != null ? s2 : "0");
        c = Integer.parseInt(s3 != null ? s3 : "0");
        d = Integer.parseInt(s4 != null ? s4 : "0");
        }
        catch(NumberFormatException ex)
        {
            System.out.println("Exception : "+ex);
        }

And also the variable s is also null so you got the NullPointerException

if (s != null && s.equals("red"))

instead of

if (s.equals("red"))

OTHER TIPS

Catch the Exception and handle it

try{    
    a=Integer.parseInt(s1);
    b=Integer.parseInt(s2);
    c=Integer.parseInt(s3);
    d=Integer.parseInt(s4);
} catch(NumberFormatException e){
    //exceptionhandling
}

Simply catch the exception in catch block and take the appropriate action.

try{
  // some code that may throw NumberFormatException 

}catch(NumberFormatException e){
  // when number format exception occur, take appropriate action
}

Root cause of your problem:

As exception says clearly
  java.lang.NumberFormatException: null 
    at java.lang.Integer.parseInt(Integer.java:443)

You are trying to parse a String value that is null into an Integer, that is why parseInt() threw an exception.

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