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\n<\/p>\n
Compare 2 lists by<\/p>\n
import java.util.Arrays;\nimport java.util.Comparator;\nimport java.util.List;\nimport java.util.Objects;\nimport java.util.function.IntFunction;\nimport java.util.stream.Collectors;\nimport java.util.stream.IntStream;\n\npublic class SortNestedList {\n\n protected List<List<Long>> transform(Long[][] inputArray) {\n return Arrays.stream(inputArray)\n .filter(Objects::nonNull) \/\/ filter outer null lists\n .map(nested -> Arrays.stream(nested)\n .filter(Objects::nonNull)\n .collect(Collectors.toList())) \/\/ generate nested list by filtering any null values\n .collect(Collectors.toList());\n }\n\n protected void sortWithElementComparator(List<List<Long>> lists) {\n lists.sort((a, b) -> {\n return IntStream.range(0, Math.min(a.size(), b.size())) \/\/ check till end of minimum sized list\n .map(i -> Long.compare(a.get(i), b.get(i))) \/\/ compare elements at same index\n .filter(i -> i != 0) \/\/ ignore equal values comparison\n .findFirst() \/\/ get first non-zero comparison result (unequal)\n .orElse(Integer.compare(a.size(), b.size())); \/\/ if nothing, then compare size\n });\n\n lists.forEach(System.out::println);\n }\n\n protected void sortWithDecoratedComparator(List<List<Long>> lists) {\n \/\/ comparator for an index\n IntFunction<Comparator<List<Long>>> elementAtIndexComparator =\n index -> (a, b) -> index < Math.min(a.size(), b.size()) ?\n Long.compare(a.get(index), b.get(index)) : \/\/ compare elements if index is valid for both lists\n Integer.compare(a.size(), b.size()); \/\/ compare size if index is invalid for atleast 1 list\n\n final int maxInnerIndices = lists.stream()\n .mapToInt(List::size)\n .max().orElse(0); \/\/ get max inner list size or 0 if empty\n\n Comparator<List<Long>> listComparator = IntStream.range(0, maxInnerIndices)\n .mapToObj(elementAtIndexComparator) \/\/ index comparator for every index\n .reduce(Comparator::thenComparing) \/\/ kind of chain of responsibility \/ decorator\n .orElse((a, b) -> 0);\n\n lists.sort(listComparator);\n\n lists.forEach(System.out::println);\n }\n\n protected void sort(Long[][] inputArray, int run) {\n System.out.println(\"Sort input using direct element comparator: \" + run);\n sortWithElementComparator(transform(inputArray));\n System.out.println(\"Sort input using decorated comparator: \" + run);\n sortWithDecoratedComparator(transform(inputArray));\n }\n}\n<\/code><\/pre>\nTest code<\/h2>\n public static void main(String[] args) {\n final SortNestedList sortNestedList = new SortNestedList();\n int run = 0;\n\n Long[][] inputArray = new Long[][]{};\n sortNestedList.sort(inputArray, ++run);\n\n inputArray = new Long[][]{{null}};\n sortNestedList.sort(inputArray, ++run);\n\n inputArray = new Long[][]{{null}, {1L}};\n sortNestedList.sort(inputArray, ++run);\n\n inputArray = new Long[][]{null, {1L}};\n sortNestedList.sort(inputArray, ++run);\n\n inputArray = new Long[][]{{1L}, {1L}};\n sortNestedList.sort(inputArray, ++run);\n\n inputArray = new Long[][]{{2L}, {1L}};\n sortNestedList.sort(inputArray, ++run);\n\n inputArray = new Long[][]{{2L, 1L}, {1L, 3L}};\n sortNestedList.sort(inputArray, ++run);\n\n inputArray = new Long[][]{{Long.MAX_VALUE, 1L}, {Long.MIN_VALUE, 3L}};\n sortNestedList.sort(inputArray, ++run);\n\n inputArray = new Long[][]{{1L}, {2L, 5L, 6L},\n {1L, 2L}, {2L}, {1L, 2L, 3L}, {3L, 2L}, {2L, 3L},\n {1L, 2L, 3L, 4L, 6L}, {1L, 2L, 3L, 4L, 5L},\n {1L, 2L, 3L, 4L, 6L, 2L}, {1L, 2L, 3L, 4L, 5L, 3L, 5L},\n {Long.MAX_VALUE, Long.MAX_VALUE, 1L, 5L, Long.MIN_VALUE + 1, Long.MAX_VALUE - 1},\n {Long.MAX_VALUE, Long.MIN_VALUE, 1L, 5L, Long.MIN_VALUE + 1, Long.MAX_VALUE - 1},\n {Long.MIN_VALUE}, {Long.MAX_VALUE}};\n sortNestedList.sort(inputArray, ++run);\n }\n<\/code><\/pre>\nThanks to Holger and WJS<\/p>\n<\/p><\/div>\n