Thread: 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)

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.

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"?

Originally Posted by The_Mexican

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.

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...