diff -r 4ebc2e2fb97c -r 71c04702a3d5 src/sample/nashorn/list_mapreduce.js --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/sample/nashorn/list_mapreduce.js Tue Sep 12 19:03:39 2017 +0200 @@ -0,0 +1,86 @@ +/* + * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * - Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * + * - Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * - Neither the name of Oracle nor the names of its + * contributors may be used to endorse or promote products derived + * from this software without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS + * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, + * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR + * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR + * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, + * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, + * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR + * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF + * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING + * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS + * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + */ + +// Usage: jjs list_mapreduce.js + +// Many Array.prototype functions such as map, +// filter, reduce, reduceRight, every, some are generic. +// These functions accept ECMAScript array as well as +// many array-like objects including java.util.ArrayLists. +// So, you can do map/filter/reduce with Java streams or +// you can also use Array.prototype functions as below. +// See also http://en.wikipedia.org/wiki/MapReduce + +var ArrayList = Java.type("java.util.ArrayList"); +var list = new ArrayList(); +list.add("nashorn"); +list.add("ecmascript"); +list.add("javascript"); +list.add("js"); +list.add("scheme"); + +var map = Array.prototype.map; +var filter = Array.prototype.filter; +var reduce = Array.prototype.reduce; + +// sum of word lengths +print("Sum word length:", + reduce.call( + map.call(list, function(x) x.length), + function(x, y) x + y) +); + +// filter use to filter out "j*" and concatenate rest with ":" +// after uppercasing all strings +print( + reduce.call( + map.call( + filter.call(list, function(x) !x.startsWith("j")), + function(x) x.toUpperCase()), + function(x, y) x + ":" + y) +); + +// another list example involving numbers +list.clear(); +// make random list of numbers +for (var i = 0; i < 10; i++) + list.add(Math.random()); + +var forEach = Array.prototype.forEach; +// print numbers in the list +forEach.call(list, function(x) print(x)); + +// print sum of squares of the random numbers +print("Square sum:", + reduce.call( + map.call(list, function(x) x*x), + function(x, y) x + y) +);