//    This applet demonstrates the use of the if statement.  
//    User input consists of a TextField and an "add" button.  
//    Positive integers input through the TextField are added 
//    to a sum when the add button is pressed.  
//    The sum is displayed.  Non-Positive integers are ignored.

import java.applet.*;
import java.awt.*;
import java.awt.event.*;

public class Lesson5 extends Applet implements ActionListener
{
   Label title = new Label("Sum Positive Integers");

   // Input panel.
   Panel inputP = new Panel(new GridLayout(1, 2));
   Label inputL = new Label("Enter integers:");
   TextField input = new TextField(15);

   // Sum output.
   Label sumL = new Label();

   // Pressing this will cause the input to be read and processed.
   Button addB = new Button("Add");

   int sum = 0;

   public void init()
   {
      setLayout(new GridLayout(4, 1));

      add(title);

      add(inputP);
      inputP.add(inputL);
      inputP.add(input);

      add(sumL);
      sumL.setText("sum: " + sum);

      add(addB);
      addB.addActionListener(this);
      setSize(200,100);
   }

    // actionPerformed handles button presses.  It is executed whenever
    // the add button is pressed.
   public void actionPerformed(ActionEvent e)
   {
      int inputI;

      // Read the input integer.
      inputI = Integer.parseInt(input.getText());

      // Ignore non-positive inputs.
      if (inputI > 0)
      {
         sum += inputI;
         sumL.setText("sum: " + sum);
      }
   }
}