Thread: using ActionListeners to draw circles

Hey there,

We're learning GUI, and I'm working on a program that takes the input of x, y, and radius, and draws a circle from those points.

I'm stuck, because in my listener, I'm not sure how to specify that I want the program to take the input from x, y, and radius JTextFields, and use the DrawOval() method to make a circle. So far I have:

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
 
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
 
public class Circle extends JPanel {
 
 
 
JButton draw = new JButton("draw circle");
JTextField xcoord = new JTextField("x-coord");
JTextField ycoord = new JTextField("y-coord");
JTextField rad = new JTextField("radius");
 
public Circle() {
	JPanel northPanel = new JPanel();
	northPanel.add(draw);
	northPanel.add(xcoord);
	northPanel.add(ycoord);
	northPanel.add(rad);
	add(northPanel);
}
 
class drawlistener implements ActionListener {
	public void actionPerformed(ActionEvent event) {
 
		String inputString = xcoord.getText();
	    int x = Integer.parseInt(inputString);
 
	    String inputString2 = ycoord.getText();
	    int y = Integer.parseInt(inputString2);
 
	    String inputString3 = rad.getText();
	    int r = Integer.parseInt(inputString3);
 
 
 
	}
}
 
 
public static void main(String[] args) {
	JFrame frame = new JFrame();
	Circle c1 = new Circle();
	frame.add(c1);
	frame.setSize(500,500);
	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	frame.setVisible(true);
 
}
 
 
}

What are the values of x, y, and r after running the code you have so far? Did it work as expected? If so, what is your question? If not, what values did you get and what did you expect?

Well, x,y, and r are just the values that the user would input into the JTextFields, then upon clicking the "draw" button, I want a circle to be drawn. I just don't know how to actually invoke the drawOval() method from inside my ActionListener.

How do you invoke the add method inside the constructor?
How do you invoke the parseInt method inside the action listener?
You call drawOval the same way you call any other method. Just type the name, open paren, any parameters if any are needed, close paren, and semicolon.

Swing's drawing or painting mechanism can be used to respond to actions on the user interface. In this case, the ActionListener that handles the button press could read and set the values x, y, and r and then call repaint() to draw the oval.

I recommend the following changes to your fundamental design:

The main class (CircleFrame) composes a JFrame in which 2 panels are placed:
1. North (or South?): A JPanel to contain the text fields and button is built in and returned from a CircleFrame method. An action listener is added to the button much as you've already done. (Class names begin with capital letters.) The action listener's actionPerformed() method reads and sets the values x, y, and r and then calls repaint() to draw the oval.
2. Center: A JPanel to draw the ovals (OvalPanel) is built from an enclosed class that extends JPanel.

The paintComponent() method of OvalPanel is overridden to draw ovals specified by x, y, and radius as set by the button's action listener which calls repaint() after the values are set.

The main() method of CircleFrame simply creates an instance of CircleFrame on the EDT, nothing else.

Good luck!