Interate over char array with another int array using streams

Question

I want to use streams in java like LINQ in .net. I have two arrays one is a char array and the other is int array. Now I looping with a foreach loop to print a message using the two arrays, one hold the chars and the other is just the positions where to pick the char.

Here is the code:

char[] letter = {115, 116, 97, 99, 107, 111, 118, 101, 114, 102, 108, 119, 105, 110, 100, 103, 32 };
int[] pos = {0,1,2,3,4,5,6,7,8,9,10,5,11,16,12,0,16,4,12,13,15};

for(int s:pos){
    System.out.print(letter[s]);
}

I want to make this using streams.

My idea was to do something like this.

Arrays.asList(
    0,1,2,3,4,5,6,7,8,9,10,5,11,16,12,0,16,4,12,13,15
)
.stream()
.forEach(p -> p)

So in the lambda expression in the forEach use the letter char array but maybe now but it straight in like

letter[p]

if i get you try this Arrays.stream(pos).forEach(p->System.out.println(letter[p])); — user16669986
– user16669986, Commented Aug 20, 2021 at 8:12

vszholobov · Accepted Answer · 2021-08-20 08:23:58Z

2

You can do it with map and access by index

public static void main(String[] args) {
    char[] letter = {115, 116, 97, 99, 107, 111, 118, 101, 114, 102, 108, 119, 105, 110, 100, 103, 32 };
    int[] pos = {0,1,2,3,4,5,6,7,8,9,10,5,11,16,12,0,16,4,12,13,15};

    Arrays.stream(pos).map(x -> letter[x]).forEach(System.out::print);
}

Output:

11511697991071111181011141021081111193210511532107105110103

If you don't want to create int[] array you can use Stream.of()

Stream.of(0,1,2,3,4,5,6,7,8,9,10,5,11,16,12,0,16,4,12,13,15)
      .map(x -> letter[x])
      .forEach(System.out::print);

But output would be

stackoverflow is king

The difference appears because in the first example the stream was started from an int array and chars later converted to int. if you want to display the word in the first example, then replace the stream with

Arrays.stream(pos)
      .mapToObj(x -> (char) letter[x])
      .forEach(System.out::print);

edited Aug 20, 2021 at 8:23

answered Aug 20, 2021 at 8:11

vszholobov

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8 Comments

codemoonger Over a year ago

Is it possible to bake in the arrays directly in the stream and not declare them outside, so everything in one big chunk of code. Also the output should be letters, without the MAP it worked

vszholobov Over a year ago

Added this to answer

codemoonger Over a year ago

Is it possible to add the letter array inside the map method,

vszholobov Over a year ago

What do you mean by add inside? It is already inside method x -> letter[x]. You want to create char array inside map?

Holger Over a year ago

@mogren3000 recreating the char array for every stream element is very expensive. If you want to treat a sequence of char values like a constant, use the old idiomatic solution that is both, readable and efficient:

IntStream.of(0,1,2,3,4,5,6,7,8,9,10,5,11,16,12,0,16,4,12,13,15) .mapToObj("stackoverflwindg "::charAt) .forEach(System.out::print);

. If you want to be even more efficient, avoid the boxing to Character objects:

IntStream.of(0,1,2,3,4,5,6,7,8,9,10,5,11,16,12,0,16,4,12,13,15) .map("stackoverflwindg "::charAt) .forEach(c -> System.out.print((char)c));

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