import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class MainPanel extends JPanel implements ActionListener {

JComboBox shapeList;

JTextField answer;
JTextField shapeSelected;
JTextField circle;
JTextField square;
JTextField triangle;
JTextField triangle3;

JLabel circle2;
JLabel square2;
JLabel triangle2;
JLabel triangle4;
JLabel triangle5;
JLabel squareAnswer;
JLabel circleAnswer;
JLabel triangleAnswer;

JButton calculate;

MainPanel()
{
    String [] shapes = {"circle", "square", "triangle"};

    shapeList = new JComboBox(shapes);
    shapeList.addActionListener(this);
    add(shapeList);
}

private void squareDraw()
{
    Graphics g = getGraphics();
    g.setColor(Color.blue);
    g.fillRect(200, 250, 100, 100);
}

private void circleDraw()
{
    Graphics g = getGraphics();
    g.setColor(Color.blue);
    g.fillOval(200, 250, 100, 100);
}

private void triangleDraw()
{
    Graphics g = getGraphics();
    g.setColor(Color.blue);
    g.fillPolygon(new int[] {50, 100, 0}, new int[] {0, 100, 100}, 3);
}

@Override
public void actionPerformed(ActionEvent e)
{
    Object o = e.getSource();

    if (o == shapeList)
    {
        if (shapeList.getSelectedItem().equals("circle"))
        {
            circle2 = new JLabel();
            circle2.setText("Radius:");
            add(circle2);

            circle = new JTextField(10);
            add(circle);

            circleAnswer = new JLabel();
            circleAnswer.setText("Area:");
            add(circleAnswer);

            answer = new JTextField(10);
            add(answer);

            calculate = new JButton("Calculate Area");
            calculate.addActionListener(this);
            add(calculate);

            this.revalidate();
            this.repaint();
        }

        if (shapeList.getSelectedItem().equals("square"))
        {
            square2 = new JLabel();
            square2.setText("Width/Height:");
            add(square2);

            square = new JTextField(10);
            add(square);

            squareAnswer = new JLabel();
            squareAnswer.setText("Area:");
            add(squareAnswer);

            answer = new JTextField(10);
            add(answer);

            calculate = new JButton("Calculate Area");
            calculate.addActionListener(this);
            add(calculate);

            this.revalidate();
            this.repaint();
        }

        if (shapeList.getSelectedItem().equals("triangle"))
        {
            triangle4 = new JLabel();
            triangle4.setText("Base:");
            add(triangle4);

            triangle = new JTextField(10);
            add(triangle);

            triangle5 = new JLabel();
            triangle5.setText("Height:");
            add(triangle5);

            triangle3 = new JTextField(10);
            add(triangle3);

            triangleAnswer = new JLabel();
            triangleAnswer.setText("Area:");
            add(triangleAnswer);

            answer = new JTextField(10);
            add(answer);

            calculate = new JButton("Calculate Area");
            calculate.addActionListener(this);
            add(calculate);

            this.revalidate();
            this.repaint();
        }
    }

    if (o == calculate)
    {
        if (shapeList.getSelectedItem().equals("square"))
        {
            double sum = Double.parseDouble(square.getText()) * Double.parseDouble(square.getText());
            answer.setText(String.valueOf(sum));

            squareDraw();
        }

        if (shapeList.getSelectedItem().equals("triangle"))
        {
            double sum = (Double.parseDouble(triangle.getText()) * Double.parseDouble(triangle3.getText())) / 2;
            answer.setText(String.valueOf(sum));

            triangleDraw();
        }

        if (shapeList.getSelectedItem().equals("circle"))
        {
            double sum = (Double.parseDouble(circle.getText()) * Double.parseDouble(circle.getText())) * Math.PI;
            answer.setText(String.valueOf(sum));

            circleDraw();
        }
    }
}
}