Java-Code

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class GrossKleinSchreibung {

	public static void main(String[] args) throws IOException {
		System.out.println("Enter text: ");
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		String text = in.readLine();
		System.out.println(manipulate(text));
	}
	/**
	 * makes all letters at position 2*k a lowerCase letter, all others upperCase.
	 * All characters will be counted, but only letters will be modified.
	 * @param text the text to manipulate
	 * @return the manipulated String
	 */
	private static String manipulate(String text){
		char[] chars = new char[text.length()];
		//copy all chars as lowerCase into array
		text.toLowerCase().getChars(0, text.length(), chars, 0);
		//make every second letter a capital one
		for(int i=0; i<chars.length; i+=2)
			chars[i] = Character.toUpperCase(chars[i]);
		//rebuilt a String and return it
		return String.copyValueOf(chars);
	}

}

Ruby-Code

#die "klassiche Lösung"
print "Texteingabe: "
text = gets.chop
ausgabe = ""
for i in 0..text.size-1 do
  if i % 2 == 0 then
    ausgabe += text[i].upcase
  else
    ausgabe += text[i].downcase
  end	
end
puts "Textausgabe: " + ausgabe

#es geht auch kürzer:
#print "Texteingabe: "
#text = gets.chop
#print "Textausgabe: "
#for i in 0..text.size-1 do
#  if i % 2 == 0 then
#    print text[i].upcase
#  else
#    print text[i].downcase
#  end	
#end
#++++++++++++++++
#oder so:
#print "Texteingabe: "
#text = gets.chop
#print "Textausgabe: "
#i = 1
#text.each_char {|c| i+=1; print c.upcase if i%2 == 0; print c.downcase if i%2 != 0}