/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
 
public static String duplicatePrefix(final String source, final int prefixLength, final int count) {
    if (source == null || source.length() == 0 || prefixLength <= 0 || count <= 0) {
        return "";
    }
 
    final int actual = Math.min(source.length(), prefixLength);
    final int size = actual * count;
    final char[] results = new char[size];
    // copy the first prefix to the output
    source.getChars(0, actual, results, 0);
    // duplicate the previously populated chars as often as needed.
    int currentpos = actual;
    while (currentpos < size) {
        // copy as much as you can, limited by the available space to copy to.
        System.arraycopy(results, 0, results, currentpos, Math.min(currentpos, size - currentpos));
        // double the current position
        currentpos <<= 1;
        System.out.println("Currently writing to " + currentpos);
    }
    return new String(results);
}
	public static void main (String[] args) throws java.lang.Exception
	{
		System.out.println(duplicatePrefix("Hello World", 5, 10));
	}
}

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