Here you can find the source of sleep(Long millis)
public static boolean sleep(Long millis)
//package com.java2s; //License from project: Apache License public class Main { public static boolean sleep(Long millis) { if (millis == null || millis <= 0) { return true; }/*from w w w . j a v a 2s . c o m*/ try { Thread.sleep(millis); } catch (InterruptedException e) { return false; } return true; } }