1 /* 2 * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 8 * - Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 11 * - Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * - Neither the name of Oracle nor the names of its 16 * contributors may be used to endorse or promote products derived 17 * from this software without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS 20 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, 21 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR 23 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 24 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 25 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 26 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 27 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 28 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 29 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 // Usage: jjs list_mapreduce.js 33 34 // Many Array.prototype functions such as map, 35 // filter, reduce, reduceRight, every, some are generic. 36 // These functions accept ECMAScript array as well as 37 // many array-like objects including java.util.ArrayLists. 38 // So, you can do map/filter/reduce with Java streams or 39 // you can also use Array.prototype functions as below. 40 // See also http://en.wikipedia.org/wiki/MapReduce 41 42 var ArrayList = Java.type("java.util.ArrayList"); 43 var list = new ArrayList(); 44 list.add("nashorn"); 45 list.add("ecmascript"); 46 list.add("javascript"); 47 list.add("js"); 48 list.add("scheme"); 49 50 var map = Array.prototype.map; 51 var filter = Array.prototype.filter; 52 var reduce = Array.prototype.reduce; 53 54 // sum of word lengths 55 print("Sum word length:", 56 reduce.call( 57 map.call(list, function(x) x.length), 58 function(x, y) x + y) 59 ); 60 61 // filter use to filter out "j*" and concatenate rest with ":" 62 // after uppercasing all strings 63 print( 64 reduce.call( 65 map.call( 66 filter.call(list, function(x) !x.startsWith("j")), 67 function(x) x.toUpperCase()), 68 function(x, y) x + ":" + y) 69 ); 70 71 // another list example involving numbers 72 list.clear(); 73 // make random list of numbers 74 for (var i = 0; i < 10; i++) 75 list.add(Math.random()); 76 77 var forEach = Array.prototype.forEach; 78 // print numbers in the list 79 forEach.call(list, function(x) print(x)); 80 81 // print sum of squares of the random numbers 82 print("Square sum:", 83 reduce.call( 84 map.call(list, function(x) x*x), 85 function(x, y) x + y) 86 );