Thread: NullPointerException when canceling JOptionPane.showInputDialog

Hello folks,

Not sure what the problem is here. When I run this code it creates directories just fine. If I hit the "cancel" button, however, it creates a directory called "null". When I attempt to check the string for null, I get a NullPointerException. Any help is greatly appreciated.

	public void makeTables() throws IOException{
		String dirPath = "data/tendtables/";
		String tname = (String)JOptionPane.showInputDialog(
				"Enter the name of the new strain:");
 
		// Canceled?
		if (tname.equals(null))
			return;
 
		// Check if directory already exists
		File tendTableDir = new File(dirPath + tname);
		if (tendTableDir.exists()){
			JOptionPane.showMessageDialog(null, "Strain already created!");
		}else{
				// Create the directory
				tendTableDir.mkdir();

If tname is null, then there is no object with an equals() method to dereference. Hence a NPE
The way to test if an object reference such as tname is null it to use ==
For example: if (tname == null) ...

Or to try/catch them NPE's. Try/catching is good practice, youll need to be adept at it later anyways . Not to mention the fact that teachers love error-handling.