Data update

Task/Goldbachs-comet/Java/goldbachs-comet.java

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+import java.awt.Color;
+import java.awt.Graphics;
+import java.awt.image.BufferedImage;
+import java.io.File;
+import java.io.IOException;
+import java.util.List;
+
+import javax.imageio.ImageIO;
+
+public final class GoldbachsComet {
+
+	public static void main(String[] aArgs) {
+		initialisePrimes(2_000_000);		
+		
+		System.out.println("The first 100 Goldbach numbers:");
+		for ( int n = 2; n < 102; n++ ) {
+			System.out.print(String.format("%3d%s", goldbachFunction(2 * n), ( n % 10 == 1 ? "\n" : "" )));
+		}
+		
+		System.out.println();
+		System.out.println("The 1,000,000th Goldbach number = " + goldbachFunction(1_000_000));
+		
+		createImage();
+	}	
+	
+	private static void createImage() {
+		final int width = 1040;
+		final int height = 860;
+		BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
+		Graphics graphics = image.getGraphics();
+        graphics.setColor(Color.WHITE);
+        graphics.fillRect(0, 0, width, height);
+		
+        List<Color> colours = List.of( Color.BLUE, Color.GREEN, Color.RED );
+        for ( int n = 2; n < 2002; n++ ) {
+        	graphics.setColor(colours.get(n % 3));
+        	graphics.fillOval(n / 2, height - 5 * goldbachFunction(2 * n), 10, 10);
+        }		
+		
+		try {
+			ImageIO.write(image, "png", new File("GoldbachsCometJava.png"));
+		} catch (IOException ioe) {
+			ioe.printStackTrace();
+		}
+	}
+	
+	private static int goldbachFunction(int aNumber) {
+		if (  aNumber <= 2 || aNumber % 2 == 1 ) {
+			throw new AssertionError("Argument must be even and greater than 2: " + aNumber);
+		}
+		
+		int result = 0;
+		for ( int i = 1; i <= aNumber / 2; i++ ) {			
+		    if ( primes[i] && primes[aNumber - i] ) {
+		    	result += 1;
+		    }
+		}
+		return result;
+	}
+	
+	private static void initialisePrimes(int aLimit) {
+		primes = new boolean[aLimit];
+		for ( int i = 2; i < aLimit; i++ ) {
+			primes[i] = true;
+		}
+		
+		for ( int n = 2; n < Math.sqrt(aLimit); n++ ) {
+			for ( int k = n * n; k < aLimit; k += n ) {
+				primes[k] = false;
+			}
+		}
+	}
+	
+	private static boolean[] primes;
+
+}