Here you can find the source of sleep(long millis)
public static void sleep(long millis)
//package com.java2s; //License from project: LGPL public class Main { public static void sleep(long millis) { try {// ww w . j a va2s . c om Thread.sleep(millis); } catch (InterruptedException interruptedException) { throw new RuntimeException("Unable to sleep for " + millis + " millis.", interruptedException); } } }