/* 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 void main (String[] args) throws java.lang.Exception
	{
        String str = "This is a test. The app should break this string in substring on whitespaces after 13 characters"; 
		System.out.println(str.replaceAll(".{13,}?[ ]", "$0\n"));
	}
}

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