{"id":448,"date":"2015-12-30T23:07:28","date_gmt":"2015-12-30T21:07:28","guid":{"rendered":"http:\/\/kra.lc\/blog\/?p=448"},"modified":"2015-12-30T23:10:43","modified_gmt":"2015-12-30T21:10:43","slug":"generic-arraycomparator-for-comparable-java-types","status":"publish","type":"post","link":"https:\/\/kra.lc\/blog\/2015\/12\/generic-arraycomparator-for-comparable-java-types\/","title":{"rendered":"Generic ArrayComparator for Comparable Java types"},"content":{"rendered":"

Another day, another post! The marathon continues.<\/a> After watching “Star Wars: The Force Awakens” yesterday<\/a>, let’s speak a few words about Open Source<\/a>. Since I began releasing my projects<\/a>, most of it has been released on a dedicated website or on this blog. Meanwhile GitHub is the main source for free and open source code, therefore I decided to create an own profile at: https:\/\/github.com\/kristian<\/strong><\/a> (yay! xD)<\/em><\/p>\n

I think GitHub is a great way to contribute to Open Source and collaborate between individuals. I’m going to release much of my stuff on GitHub, but add a few more words about it here in my blog. Some smaller snippets will stay though, such as one thing, that I was surprised is not part of the Java standard libraries yet: A generic ArrayComparator<\/code> for Comparable<\/code> Java types.<\/p>\n

<\/p>\n

The task was quite simple, I wanted to sort a Collection<\/code> of arrays in Java. To do so, I wanted to use a TreeMap<\/code> to sort it’s elements, while adding elements to the SortedMap<\/code>. Unfortunately arrays in Java do not implement the Compareable<\/code> interface by default. So a Comparator<\/code> was needed. Much to my surpise, I found no ArrayComparator<\/code>, neither in the standard Java library code, nor on any source on the internet. Here’s my implementation of a generic ArrayComparator<\/code> class:<\/p>\n

\r\npublic class ArrayComparator<T extends Comparable<T>> implements Comparator<T[]> {\r\n\t@Override public int compare(T[] arrayA, T[] arrayB) {\r\n\t\tif(arrayA==arrayB) return 0; int compare;\r\n\t\tfor(int index=0;index<arrayA.length;index++)\r\n\t\t\tif(index<arrayB.length) {\r\n\t\t\t\tif((compare=arrayA[index].compareTo(arrayB[index]))!=0)\r\n\t\t\t\t\treturn compare;\r\n\t\t\t} else return 1; \/\/first array is longer\r\n\t\tif(arrayA.length==arrayB.length)\r\n\t\t\t   return 0; \/\/arrays are equal\r\n\t\telse return -1; \/\/first array is shorter \r\n\t}\r\n}\r\n<\/pre>\n
There is only one prerequisite for the comparator though, the generic base type of the array must implement the Comparable<\/code> interface. Now sorting multi-dimensional arrays, Collections<\/code>, or (Sorted)Maps<\/code> really becomes a piece of cake! Let me share a few examples:<\/p>\n
\r\nString[][] sorted = new String[][]{{"A","B"},{"B","C"},{"A","C"}};\r\nArrays.sort(sorted, new ArrayComparator<>());\r\n<\/pre>\n
\r\nList<String[]> sorted = new ArrayList<>();\r\nsorted.add(new String[]{"A","B"});\r\nsorted.add(new String[]{"B","C"});\r\nsorted.add(new String[]{"A","C"});\r\nsorted.sort(new ArrayComparator<>());\r\n<\/pre>\n
\r\nMap<String[],Object> sorted = new TreeMap<>(new ArrayComparator<>());\r\nsorted.put(new String[]{"A","B"}, new Object());\r\nsorted.put(new String[]{"B","C"}, new Object());\r\nsorted.put(new String[]{"A","C"}, new Object());\r\n<\/pre>\n
I hope you find this little code snippet useful. Stay tuned for the forth post of my little coding marathon tomorrow<\/em>.<\/p>\n","protected":false},"excerpt":{"rendered":"
Another day, another post! The marathon continues. After watching “Star Wars: The Force Awakens” yesterday, let’s speak a few words about Open Source. Since I began releasing my projects, most of it has been released on a dedicated website or on this blog. Meanwhile GitHub is the main source for free and open source code, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[200,202,203,201,204,53,5],"class_list":["post-448","post","type-post","status-publish","format-standard","hentry","category-release","tag-array","tag-arraycomparator","tag-comparable","tag-comparator","tag-compare","tag-generic","tag-java"],"_links":{"self":[{"href":"https:\/\/kra.lc\/blog\/wp-json\/wp\/v2\/posts\/448","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/kra.lc\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/kra.lc\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/kra.lc\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/kra.lc\/blog\/wp-json\/wp\/v2\/comments?post=448"}],"version-history":[{"count":26,"href":"https:\/\/kra.lc\/blog\/wp-json\/wp\/v2\/posts\/448\/revisions"}],"predecessor-version":[{"id":474,"href":"https:\/\/kra.lc\/blog\/wp-json\/wp\/v2\/posts\/448\/revisions\/474"}],"wp:attachment":[{"href":"https:\/\/kra.lc\/blog\/wp-json\/wp\/v2\/media?parent=448"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/kra.lc\/blog\/wp-json\/wp\/v2\/categories?post=448"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/kra.lc\/blog\/wp-json\/wp\/v2\/tags?post=448"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}