This is a java program with two buttons used to change an integer value and display it. However in IntelliJIDEA the two lines with
increase.addActionListener(incListener());
decrease.addActionListener(decListener());
keep displaying errors 'Method call expected'.
I am not sure what to do to fix this.
Any help will be greatly appreciated
Thanks
Note: the full code is attached below.
import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class Main extends JDialog {
public JPanel contentPane;
public JButton decrease;
public JButton increase;
public JLabel label;
public int number;
public Main() {
setContentPane(contentPane);
setModal(true);
increase = new JButton();
decrease = new JButton();
increase.addActionListener(incListener());
decrease.addActionListener(decListener());
number = 50;
label = new JLabel();
}
public class incListener implements ActionListener {
public void actionPerformed (ActionEvent event) {
number++;
label.setText("" + number);
}
}
public class decListener implements ActionListener {
public void actionPerformed (ActionEvent event) {
number--;
label.setText("" + number);
}
}
public static void main(String[] args) {
Main dialog = new Main();
dialog.pack();
dialog.setVisible(true);
System.exit(0);
}
}
7 Answers
incListener and declListener are classes, not methods.
Try
increase.addActionListener(new incListener());
btw, rename your classes names to make them start with an uppercase
It's simple: use new incListener() instead of incListener(). The later is trying to call a method named incListener, the former creates an object from the class incListener, which is what we want.
incListener and decListener are a classes but not a methods, so you must call new to use them, try this:
increase.addActionListener(new incListener()); decrease.addActionListener(new decListener());
sorry for my bad english
substitute the lines with
increase.addActionListener( new incListener());
decrease.addActionListener( new decListener());
Make these changes:
public Main() {
contentPane = new JPanel();
setContentPane(contentPane);
setModal(true);
increase = new JButton("inc");
decrease = new JButton("dec");
contentPane.add(increase);
contentPane.add(decrease);
increase.addActionListener(new incListener());
decrease.addActionListener(new decListener());
number = 50;
label = new JLabel(number+"");
contentPane.add(label);
}
It's sad but I had to Google this same error... I was staring at a method that returned a class. I left off the new operator.
return <class>(<parameters>)
vs
return new <class>(<parameters>)
Whenever a string object is created using new operator a new object is created which is what your program is looking for. The following link is useful in learning about the difference between a string and a new string. What is the difference between "text" and new String("text")?
