Sort ArrayList of Array in Java
You create a Comparator<String[]>
like so:
new Comparator<String[]>() {
public int compare(String[] first, String[] second) {
return first[1].compareTo(second[1]);
}
}
then pass it to Collections.sort()
.
You might want to do some checking if the second element is actually present in the array. You could also do a custom comparison if the standard String comparison isn't enough.
You write a Comparator
that compares two String[]
by the correct child, and then you pass it to Collections.sort(List<T> list, Comparator<? super T> c)
.
Start with Collections.sort, the one that takes a custom Comparator. You'll need to write a custom Comparator for this also.
For instance, assuming you want to rely on the natural ordering of Strings as defined in their compareTo method:
public static void main(String[] args) throws Exception {
ArrayList<String[]> listOfStringArrays = new ArrayList<String[]>();
listOfStringArrays.add(new String[] {"x","y","z"});
listOfStringArrays.add(new String[] {"a","b","c"});
listOfStringArrays.add(new String[] {"m","n","o"});
Collections.sort(listOfStringArrays,new Comparator<String[]>() {
public int compare(String[] strings, String[] otherStrings) {
return strings[1].compareTo(otherStrings[1]);
}
});
for (String[] sa : listOfStringArrays) {
System.out.println(Arrays.toString(sa));
}
/* prints out
[a, b, c]
[m, n, o]
[x, y, z]
*/
}
This is extremely easy to do with Java 8. Just write:
list.sort(Comparator.comparing(a -> a[1]));
For example, the following code:
List<String[]> list = Arrays.asList(
new String[] { "abc", "abc", "abc", "abc", "abc", "abc", "abc" },
new String[] { "xyz", "xyz", "xyz", "xyz", "xyz", "xyz", "xyz" },
new String[] { "fgh", "fgh", "fgh", "fgh", "fgh", "fgh", "fgh" });
list.sort(Comparator.comparing(a -> a[1]));
list.stream().map(Arrays::toString).forEach(System.out::println);
Will yield the wanted result:
[abc, abc, abc, abc, abc, abc, abc]
[fgh, fgh, fgh, fgh, fgh, fgh, fgh]
[xyz, xyz, xyz, xyz, xyz, xyz, xyz]