Here you can find the source of emptyDeque()
@SuppressWarnings("unchecked") public static <T> Deque<T> emptyDeque()
//package com.java2s; //License from project: Apache License import java.util.ArrayDeque; import java.util.Deque; public class Main { @SuppressWarnings("rawtypes") public static final Deque EMPTY_DEQUE = new ArrayDeque(); @SuppressWarnings("unchecked") public static <T> Deque<T> emptyDeque() { return EMPTY_DEQUE; }//from w w w.j av a 2 s . c o m }