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Java_Intro/HelloWorld.java

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+/**************************************************/
+/* Java Lab 1 i Programspråk                      */
+/**************************************************/
+/* Textsträng som fladdrar runt i appleten        */
+/**************************************************/
+/* Christian Ohlsson di7chro@cse.kau.se           */
+/**************************************************/
+import java.applet.*;
+import java.awt.*;
+import java.awt.image.*;
+
+public class HelloWorld extends Applet
+    implements Runnable {
+    
+    Thread animationThread = null;
+    int delay=100, xspeed, yspeed;
+    int xsize, ysize, xOffset, yOffset, helloTextWidth,
+	helloTextHeight;
+    Image backBuffer;
+    Graphics backGC; // Graphics Context
+    String helloText;
+    
+    // Initialize the Applet
+    public void init() {
+	xsize=getSize().width;
+	ysize=getSize().height;
+	backBuffer = createImage(xsize, ysize);
+	backGC = backBuffer.getGraphics();
+	
+	// Get the text from the html page that the user wants to scroll
+	helloText=getParameter("text");
+	String s=getParameter("speed");
+	xspeed=yspeed= Integer.parseInt(s);
+	
+	// Calculate the real size of the string using the font
+	FontMetrics fontInfo=backGC.getFontMetrics();
+	helloTextWidth=fontInfo.stringWidth(helloText);
+	helloTextHeight=fontInfo.getHeight();
+	xOffset=5;
+	yOffset=5;
+	yOffset=helloTextHeight;
+    }
+
+    // This method is called when the applet becomes visible
+    public void start() {
+	// Create a thread and start it
+	if(animationThread == null) {
+	    animationThread = new Thread(this);
+	    animationThread.start();
+	}
+    }
+
+    // This method is called when the applet becomes invisible
+    public void stop() {
+	// Stop animation thread
+	animationThread = null;
+    }
+
+public void run() {
+        long time = System.currentTimeMillis();
+        while(animationThread != null) {
+            // Use a constant frame rate based on the system clock
+            try {
+                time += delay;
+                Thread.sleep(Math.max(0, time -
+                                      System.currentTimeMillis()));
+            } catch (InterruptedException e) {}
+            
+            // initiate a repaint of the screen
+            repaint();
+        }
+    }
+
+    public void paint(Graphics g) {
+        // Clear the screen
+        backGC.setColor(Color.yellow);
+        backGC.fillRect(0,0,xsize,ysize);
+        
+        // Draw text 
+        backGC.setColor(Color.black);
+        backGC.drawString(helloText, xOffset, yOffset);
+        
+        xOffset-=xspeed;
+	if(xOffset <= 1)
+		xspeed = -xspeed;
+	if(xOffset+helloTextWidth >= xsize)
+		xspeed = -xspeed;
+
+        yOffset-=yspeed;
+	if(yOffset <= 5)
+		yspeed = -yspeed;
+
+	if(yOffset+helloTextHeight >= ysize)
+		yspeed = -yspeed;
+
+        // Copy the backbuffer to the screen
+        g.drawImage(backBuffer, 0, 0, this);
+    }
+    public void update(Graphics g) {
+	paint(g);
+    }
+
+}
+