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Thread: String to Int messing up

  1. #1
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    Default String to Int messing up

    Hi, I have a problem where when I try to convert a string to an int, an error comes up. I'm converting the string from a text file so that probably has something to do with it. The text file has nothing on it, so I would think it would read, ""(nothing). Here is the relevant code:

    static File file = new File("temp");
    static String dir = file.getAbsolutePath().substring(0, file.getAbsolutePath().length() - 4 );
    File rfile3 = new File(dir + "linenum.txt");
    ...
                           FileInputStream fis4 = null;
    	                BufferedInputStream bis4 = null;
    	                DataInputStream dis4 = null;
    ...
    	                fis4 = new FileInputStream(rfile3);
    	                  bis4 = new BufferedInputStream(fis4);
    	                  dis4 = new DataInputStream(bis4);
    	                  String rlinenumRead = dis4.readLine();
    	                  System.out.println(rlinenumRead); //This line yields "null"
    	                  if(rlinenumRead.equals(null)||rlinenumRead.equals("")||rlinenumRead.equals("null")) //**
    	                  {
    	               	        rlinenumRead.equals("0");
    	                  }
    	                  int rlinenumInt = Integer.parseInt(rlinenumRead);

    **=I'm trying multiple possibilities of what it could read as.

    Here is the error I'm getting:

     

    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at layout.testing2.actionPerformed(testing2.java:337) //This is the line I starred above
    at javax.swing.AbstractButton.fireActionPerformed(Unk nown 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.mouseRe leased(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(U nknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unkno wn 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.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilter s(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(U nknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarch y(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)




  2. #2
    Super Moderator copeg's Avatar
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    Default Re: String to Int messing up

    Note the readLine int DataInputStream is deprecated (BufferedReader is recommended). Also note that the readLine methods in the readers will return null if the end of the stream is reached.

  3. #3
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    Default Re: String to Int messing up

    If it returns null, then why wouldn't
    if(rlinenumRead.equals(null))
    work? Is that not how I'm suppose to say "if the string returns null"?

  4. #4
    Super Moderator copeg's Avatar
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    Default Re: String to Int messing up

    Quote Originally Posted by The_Mexican View Post
    If it returns null, then why wouldn't
    if(rlinenumRead.equals(null))
    work? Is that not how I'm suppose to say "if the string returns null"?
    Because rlinenumRead is not an object, it is null, so by definition a NullPointerException will be thrown. Try using
    if ( rlinenumRead == null )
    to check for a null value.

  5. #5
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    Default Re: String to Int messing up

    Ok you're right, and I also had to change
    rlinenumRead.equals("0");
    to
    rlinenumRead = ("0");
    Strange...I remember being taught that with strings, you use .equals instead of equal signs...

  6. #6
    Super Moderator copeg's Avatar
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    Default Re: String to Int messing up

    You should use equals, so don't change to ==. The exception (pun intended) is if there is a possibility that the string you wish to call equals on could be null, in which case you first check for null, then check equals
    String s1 = "test";
    Stirng s2 = null;
    if ( s1 != null ){
        if ( s1.equals("test")){
            //do something
        }
    }
    if ( s2 != null ){
        if ( s2.equals("test") ){
     
        }
    }
    Last edited by copeg; November 28th, 2010 at 03:14 PM.

  7. The Following User Says Thank You to copeg For This Useful Post:

    The_Mexican (November 28th, 2010)

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