Null pointer when calling a method in another class

Question

I have an input panel and want to call a method in another class when the button is pressed but am getting a null pointer exception. Was hoping someone might be able to tell me what I'm doing wrong?

Here is the code causing it:

public void actionPerformed(ActionEvent ae)
    {
        if (ae.getSource() == resultsButton)
        {
            jbTour.processAdditionalResult();
        }

    }


public void processAdditionalResult()
    {
        System.out.println("button pressed");
    }

Answer 1

您需要初始化jbTour： jbTour = new JBTourObject() （或其他），以便在调用actionPerformed方法之前它不为null。

Answer 2

I think I can tell even without the stack trace: jbTour is null. You've declared a name of that reference type in the class that implements the ActionListener interface, but you never initialized it to point a new reference.

Answer 3

If this throws a NullPointerException

jbTour.processAdditionalResult();

that means jbTour has not been set or is null .