Here you can find the source of substring(final String lhs, final BigInteger _start, final BigInteger _end)
public static String substring(final String lhs, final BigInteger _start, final BigInteger _end)
//package com.java2s; import java.math.*; public class Main { public static String substring(final String lhs, final BigInteger _start, final BigInteger _end) { int start = _start.intValue(); int end = _end.intValue(); return lhs.substring(start, end); }/*from www . ja va2 s . c om*/ }