Reputation: 1169
I am about to create the two dimensional array from string:
char[][] chars;
String alphabet = "abcdefghijklmnopqrstuvwxyz";
So the array will ilustrate this matrix:
But how can I do that using Java 8 Streams, cause I do not want to do this by casual loops ?
Upvotes: 2
Views: 1259
Reputation: 140554
Poor loops. They get such a bad rap. I doubt a streams-based solution would be as clear as this:
int n = alphabet.length();
char[][] cs = new char[n][n];
for (int i = 0; i < n; ++i) {
for (int j = 0; j < n; ++j) {
cs[i][j] = alphabet.charAt((i + j) % n);
}
}
If I had to do it with streams, I guess I'd do something like this:
IntStream.range(0, n)
.forEach(
i -> IntStream.range(0, n).forEach(j -> cs[i][j] = alphabet.charAt((i + j) % n)));
Or, if I didn't care about creating lots of intermediate strings:
cs = IntStream.range(0, n)
.mapToObj(i -> alphabet.substring(i) + alphabet.substring(0, i))
.map(String.toCharArray())
.toArray(new char[n][]);
A slightly more fun way to do it:
char[][] cs = new char[n][];
cs[0] = alphabet.toCharArray();
for (int i = 1; i < n; ++i) {
cs[i] = Arrays.copyOfRange(cs[i-1], 1, n+1);
cs[i][n-1] = cs[i-1][0];
}
Upvotes: 9
Reputation: 50776
You can use Stream.iterate()
to rotate each string incrementally and then convert them to char
arrays:
chars = Stream.iterate(alphabet, str -> str.substring(1) + str.charAt(0))
.limit(alphabet.length())
.map(String::toCharArray)
.toArray(char[][]::new);
Or you can rotate each string by its index, with Apache's StringUtils.rotate()
:
chars = IntStream.range(0, alphabet.length())
.mapToObj(i -> StringUtils.rotate(alphabet, -i))
.map(String::toCharArray)
.toArray(char[][]::new);
Or with Guava's Chars
utility class:
chars = Stream.generate(alphabet::toCharArray)
.limit(alphabet.length())
.toArray(char[][]::new);
IntStream.range(0, chars.length)
.forEach(i -> Collections.rotate(Chars.asList(chars[i]), -i));
Upvotes: 2