• Post Reply
  • Bookmark Topic Watch Topic
  • New Topic

null pointer exception

 
terry oliver
Greenhorn
Posts: 22
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
help can anyone help it does compile and thows the exception at runtime.

private void okButton_actionPerformed(ActionEvent e)
{
System.out.println("\nokButton_actionPerformed(ActionEvent e) called.");

nt.setSteel(Double.parseDouble(newSteelSize.getText()));
System.out.println("adjused steel = "+nt.getSteel());
this.dispose();
}
 
Ernest Friedman-Hill
author and iconoclast
Marshal
Pie
Posts: 24208
35
Chrome Eclipse IDE Mac OS X
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
A NullPointerException happens when something directly to the left of a "." or "[" operator is null at the time the line of code executes. Here, that could be the variables "nt" or "newSteelSize". Carefully check the code elsewhere in your application that's supposed to set those to some value.

One beginner mistake that's very likely to be the cause of this: make sure that in your class's constructor, you're not accidentally declaring local variables with the same names as these members. You should be writing

nt = ...

not

Whatever nt = ...

The stack trace should tell you exactly which line the error occurred on; it's probably that "setSteel" line, since both variables are used there.
 
Bruno Giminiani
Greenhorn
Posts: 1
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hi Terry, there is a list of top ten error by java programmers.
"Null Pointer" is the FIRST. See the link: http://www.javacoffeebreak.com/articles/toptenerrors.html

Greetings,
Bruno Giminiani
 
  • Post Reply
  • Bookmark Topic Watch Topic
  • New Topic