import java.awt.GridLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.Font;

import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.UIManager;
import javax.swing.plaf.FontUIResource;

/**
   A simple user-interface for computing the area of
   a triangle.   We have places to input the base and height,
   and a place to read out the area.

   We'll use the grid layout with two columns and three rows,
   laid out something like this:
   <pre>
   base             _(field to enter base)___
   height           _(field to enter height)_
   compute button   _(field that gets area)__
   </pre>

   @author P. Conrad
   @version 2011-01-01

 */

public class MyJFrame extends JFrame {

    private JLabel  baseLabel;
    private JLabel  heightLabel;
    private JButton computeAreaButton;

    private JTextField baseTextField;
    private JTextField heightTextField;
    private JTextField areaTextField;

    public MyJFrame() {
	super("Compute Area Of Triangle, My Friends"); // superclass constructor sets the title
	setLayout(new GridLayout(3,2)); // rows, columns

	FontUIResource fbold = new FontUIResource(Font.SANS_SERIF,Font.BOLD,24);
	FontUIResource fplain = new FontUIResource(Font.SANS_SERIF,Font.PLAIN,24);
	UIManager.put("Label.font", fbold);
	UIManager.put("Button.font", fbold);
	UIManager.put("TextField.font", fplain);

	baseLabel = new JLabel("base");
	baseTextField = new JTextField(10); // 10 wide, and initially empty
	baseTextField.setToolTipText("enter a floating point number for triangle base");

	heightLabel = new JLabel("height");
	heightTextField = new JTextField(10); // 10 wide, and initially empty
	heightTextField.setToolTipText("enter a floating point number for triangle height");

	computeAreaButton = new JButton("Compute Area");
	computeAreaButton.setToolTipText("click when data has been entered");
	areaTextField = new JTextField(10);
	areaTextField.setEditable(false); // not an editable field

	// add everything to the panel
	// note how the code is formatted to resemble the grid layout!


	add(baseLabel);         add(baseTextField);
	add(heightLabel);       add(heightTextField);
	add(computeAreaButton); add(areaTextField);

	/* 
        // this is here for demoing the way GridLayout
	// deals with extra stuff...
	JLabel extraStupidField = new JLabel("This is dumb");
	add(extraStupidField);
	*/

	// The only thing we want to wait for is a click on the button

	MyHandler handler = new MyHandler();
	computeAreaButton.addActionListener(handler);
	

    } // MyJFrame

    // inner class 

    private class MyHandler implements ActionListener {
	public void actionPerformed(ActionEvent event) {

	    // the only thing we are expecting is a button press
	    if (event.getSource()!=computeAreaButton) 
		return;
	    
	    // So the button was pressed.  Let's validate
	    // that the contents of baseTextField and 
	    // heightTextField can be converted to double.
	    // For each one, if its not valid, set it to zero.

	    double base = getDoubleValue(baseTextField);
	    double height = getDoubleValue(heightTextField);
	    
	    // Here is where in a true MVC app we'd
	    // separate out the computation.  For now,
	    // just hard code it.

	    double area=0.5 * base * height;

	    // format answer as string, and put back into field
	    String areaAsString = String.format("%f",area);
	    areaTextField.setText(areaAsString);
	    
	} // actionPerformed

	/** Get a double value from a JTextField.  As a
	    side-effect, if the value is not valid as a double,
	    force the field's value to "0.0", and return 0.0 

	@param the JTextField to operate on 
	*/

	public double getDoubleValue(JTextField jtf) {
	    String currValue = jtf.getText();
	    double value = 0.0;
	    try {
		value = Double.parseDouble(currValue);
	    } catch (NumberFormatException nfe) {
		jtf.setText("0.0");
		value = 0.0;
	    }
	    return value;
	}

    }// innerclass MyHandler
} // outerclass MyJFrame