User Input

The Echo Applet

Look over the code and try out the sample applet.

The only tricky part of this applet is in the init method. There you will see what is known as an inner class. The inner class is everything inside the following block of code:

    this.addKeyListener(new KeyAdapter(){

    });

Just before the beginning of this inner class you will notice a line that looks like this:

  requestFocus();

The inner class and the requestFocus() line enable the applet to take input from the keyboard. You will notice that within the inner class (which happens to be an instance of the KeyAdapter class), a single method is defined called keyPressed. The code within keyPressed basically runs this applet. It defines what to do when the ENTER key is pressed, when the DELETE key is pressed, when the BACKSPACE key is pressed, and when any other key is pressed. Here's the if-else block skeleton:

        if(k.getKeyCode() == KeyEvent.VK_ENTER){
        }
        else if(k.getKeyCode() == KeyEvent.VK_DELETE){
        }
        else if(k.getKeyCode() == KeyEvent.VK_BACK_SPACE){
        }
        else{
        }

Finally, at the end of this method the repaint() method is called which allows the display to be updated.
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HIGHEST PEAKS APPLET
Here's another example for you to inspect.

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

public class peaks extends Applet{
  String input, output;
  
  public void init(){
    setBackground(Color.green);
    input = "";
    output = "";
    requestFocus();
    this.addKeyListener(new KeyAdapter(){
      public void keyPressed(KeyEvent k) { 
        if(k.getKeyCode() == KeyEvent.VK_ENTER){
          if(input.equals("California")) output="Mt. Whitney";
          else if(input.equals("Nevada") ) output = "Boundary Peak";
          else if(input.equals("Arizona") ) output = "Humphrey's Peak";
          else if(input.equals("South Dakota") ) output = "Harney Peak";
          else if(input.equals("Colorado") ) output = "Mt. Elbert";
          else if(input.equals("Oregon") ) output = "Mt. Hood";
          else if(input.equals("Washington") ) output = "Mt. Ranier";
          else if(input.equals("Idaho") ) output = "Borah Peak";
          else if(input.equals("Montana") ) output = "Granite Peak";
          else if(input.equals("Utah") ) output = "King's Peak";
          else if(input.equals("Wyoming") ) output = "Gannett Peak";
          else if(input.equals("New Mexico") ) output = "Wheeler Peak";
          else output = "State Not Recognized";
        } 
        else if(k.getKeyCode() == KeyEvent.VK_DELETE){
          input = "";
          output = "";
        }
        else if(k.getKeyCode() == KeyEvent.VK_BACK_SPACE &&
                input.length() > 0 ){
          input = input.substring(0,input.length()-1);
          output = "";
        }
        else if(k.getKeyCode() != KeyEvent.VK_SHIFT){
          input += k.getKeyChar();
        }
        repaint();
      }
    });
  }

public void paint(Graphics g){
    g.setColor(Color.black);
    g.drawString("Western High Points", 10, 20);
    g.drawString("INPUT: "+input, 10, 40);
    g.drawString("OUTPUT: "+output, 10, 60);
  }
}
//<applet code=peaks.java width=200 height=80></applet>

The important part of this code to take a close look at is the part where the output is determined. This is done in a series of if and if-else statements. Make sure you understand how this works and try out the applet to make doubly sure that you understand why it behaves as it does.

NOTE: Alaska and Hawaii were intentionally left out of this applet.

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Assignment:

Create an applet which provides a list of twelve foods for the user to select from. The user selects foods by typing the name of a food. When a food is selected the cost of that item is provided as output.