Say I have two string arrays:
String[] first = new String[]{"12","23","44","67"};
String[] second= new String[]{"12","22","46","67"};
I searched for a function like PHP's array_diff which will give me the difference of these two arrays like this:
{"23","44"}
Is there a in-built function for this operation, or should I create a for loop and check for the differences ?
You can create two Sets from these arrays, like:
List<String> firstList = Arrays.asList(first);
List<String> secondList = Arrays.asList(second);
Set<String> firstSet = new HashSet<String>(first);
Set<String> secondSet = new HashSet<String>(second);
and then use the removeAll method:
firstSet.removeAll(secondList);
secondSet.removeAll(firstList);
so now firstList contains all the elements that are only available in the first array and secondList only the elements available in the second array.
A set that will contain only the elements available in one of the sets (without elements available in both sets) can be created using:
new HashSet<String>(firstSet).addAll(secondSet);
Set<String> firstSet = new HashSet<String>(first); gives "Connot resolve constructor Hashset(java.lang.String[])" error. Can Hashset be constructed like this?Guava's Sets class has a difference method.
so
Set<String> diff = Sets.difference(newHashSet(first), newHashSet(second));
PHP arrays are not arrays at all, that's why there is such weird method for diff.
If you want difference between two sets (A - B) in mathematical sense, then
1) use sets
Set<Integer> set1 = new HashSet<Integer>();
Set<Integer> set2 = new HashSet<Integer>();
2) use difference method (contains all elements in set1 that not in set2)
set1.removeAll(set2)
Note, this is assymetric difference.
List<String> first = new ArrayList<String>(Arrays.asList("12", "23");instead ofString[].Arrays.asListreturns aList, why would you pass this to aListconstructor? Second, depending on the use case an array is a perfectly acceptable data structure."12","22","23","67", what would he diff be?Arrays.asList, the returned list implements some of the methods (e.g.add()) of theListinterface by throwing an exception. I do not know the circumstances under which the OP wants to use the Strings and therefore choose the more flexible version.