Loading Images

JavaMan1.java Applet that loads an image from a relative URL.
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import java.applet.Applet;
import java.awt.*;

/** An applet that loads an image from a relative URL. 
 *
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public class JavaMan1 extends Applet {
  private Image javaMan;

  public void init() {
    javaMan = getImage(getCodeBase(),"images/Java-Man.gif");
  }

  public void paint(Graphics g) {
    g.drawImage(javaMan, 0, 0, this);
  }
}
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JavaMan2.java Illustrates loading an image from an absolute URL.
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import java.applet.Applet;
import java.awt.*;
import java.net.*;

/** An applet that loads an image from an absolute
 *  URL on the same machine that the applet came from.
 *
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public class JavaMan2 extends Applet {
  private Image javaMan;

  public void init() {
    try {
      URL imageFile = new URL("http://www.corewebprogramming.com" +
                              "/images/Java-Man.gif");
      javaMan = getImage(imageFile);
    } catch(MalformedURLException mue) {
      showStatus("Bogus image URL.");
      System.out.println("Bogus URL");
    }
  }

  public void paint(Graphics g) {
    g.drawImage(javaMan, 0, 0, this);
  }
}
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# JavaMan3.java An application that loads an image from a local file. Uses the following image and two files:

    * Java-Man.gif which should be placed in images subdirectory.
    * WindowUtilities.java Simplifies the setting of native look and feel.
    * ExitListener.java WindowListener to support terminating the application.
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JavaMan3.java
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import java.awt.*;
import javax.swing.*;

/** An application that loads an image from a local file. 
 *  Applets are not permitted to do this.
 *
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class JavaMan3 extends JPanel {
  private Image javaMan;

  public JavaMan3() {
    String imageFile = System.getProperty("user.dir") +
                       "/images/Java-Man.gif";
    javaMan = getToolkit().getImage(imageFile);
    setBackground(Color.white);
  }

  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.drawImage(javaMan, 0, 0, this);
  }
  
  public static void main(String[] args) {
    JPanel panel = new JavaMan3();
    WindowUtilities.setNativeLookAndFeel();
    WindowUtilities.openInJFrame(panel, 380, 390);
  }   
}
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Preload.java An application that demonstrates the effect of preloading an image before drawing. Specify -preload as a command-line argument to preload the image. In this case, the prepareImage method is called to immediately start a thread to load the image. Thus, the image is ready to display when the user later selects the Display Image button. 
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import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.net.*;

/** A class that compares the time to draw an image preloaded
 *  (getImage, prepareImage, and drawImage) vs. regularly
 *  (getImage and drawImage).
 *  


 *  The answer you get the regular way is dependent on the
 *  network speed and the size of the image, but if you assume
 *  you load the applet "long" (compared to the time the image
 *  loading requires) before pressing the button, the drawing
 *  time in the preloaded version depends only on the speed of
 *  the local machine.
 *
 **********************

public class Preload extends JPanel implements ActionListener {

  private JTextField timeField;
  private long start = 0;
  private boolean draw = false;
  private JButton button;
  private Image plate;

  public Preload(String imageFile, boolean preload) {
    setLayout(new BorderLayout());
    button = new JButton("Display Image");
    button.setFont(new Font("SansSerif", Font.BOLD, 24));
    button.addActionListener(this);
    JPanel buttonPanel = new JPanel();
    buttonPanel.add(button);
    timeField = new JTextField(25);
    timeField.setEditable(false);
    timeField.setFont(new Font("SansSerif", Font.BOLD, 24));
    buttonPanel.add(timeField);
    add(buttonPanel, BorderLayout.SOUTH);
    registerImage(imageFile, preload);

  }

  /** No need to check which object caused this,
   *  since the button is the only possibility.
   */

  public void actionPerformed(ActionEvent event) {
    draw = true;
    start = System.currentTimeMillis();
    repaint();
  }

  // Do getImage, optionally starting the loading.

  private void registerImage(String imageFile, boolean preload) {
    try {
      plate = getToolkit().getImage(new URL(imageFile));
      if (preload) {
        prepareImage(plate, this);
      }
    } catch(MalformedURLException mue) {
      System.out.println("Bad URL: " + mue);
    }
  }

  /** If button has been clicked, draw image and
   *  show elapsed time. Otherwise, do nothing.
   */

  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    if (draw) {
      g.drawImage(plate, 0, 0, this);
      showTime();
    }
  }

  // Show elapsed time in textfield.

  private void showTime() {
    timeField.setText("Elapsed Time: " + elapsedTime() +
                      " seconds.");
  }

  // Time in seconds since button was clicked.

  private double elapsedTime() {
    double delta = (double)(System.currentTimeMillis() - start);
    return(delta/1000.0);
  }

  public static void main(String[] args) {
    JPanel preload;

    if (args.length == 0) {
      System.out.println("Must provide URL");
      System.exit(0);
    }
    if (args.length == 2 && args[1].equals("-preload")) {
      preload = new Preload(args[0], true);
    } else {
      preload = new Preload(args[0], false);
    }

    WindowUtilities.setNativeLookAndFeel();
    WindowUtilities.openInJFrame(preload, 1000, 750);
  }
}
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