How to Loop and Print 2D array using Java 8

Question

Consider this two dimentional array

String[][] names = { {"Sam", "Smith"},
                     {"Robert", "Delgro"},
                     {"James", "Gosling"},
                   };

Using the classic way, if we want to access each element of a two dimensional array, then we need to iterate through two dimensional array using two for loops.

for (String[] a : names) {
    for (String s : a) {
        System.out.println(s);
    }
}

Is there a new elegant way to loop and Print 2D array using Java 8 features (Lambdas,method reference,Streams,...)?

What I have tried so far is this:

Arrays.asList(names).stream().forEach(System.out::println);

Output:

[Ljava.lang.String;@6ce253f1
[Ljava.lang.String;@53d8d10a
[Ljava.lang.String;@e9e54c2

How do your Strings become ints in the middle of your operation? — Holger
– Holger, Commented May 6, 2015 at 10:40
Ooops sorry. I have edited the code from for (int[] a : names) { for (int i : a) { System.out.println(i); } } to for (String[] a : names) { for (String s : a) { System.out.println(s); } } Thanks @Holger — MChaker
– MChaker, Commented May 6, 2015 at 11:57

Radiodef · Accepted Answer · 2015-05-06 01:50:23Z

23

Keeping the same output as your for loops:

Stream.of(names)
    .flatMap(Stream::of)
        .forEach(System.out::println);

(See Stream#flatMap.)

Also something like:

Arrays.stream(names)
    .map(a -> String.join(" ", a))
        .forEach(System.out::println);

Which produces output like:

Sam Smith
Robert Delgro
James Gosling

(See String#join.)

Also:

System.out.println(
    Arrays.stream(names)
        .map(a -> String.join(" ", a))
            .collect(Collectors.joining(", "))
);

Which produces output like:

Sam Smith, Robert Delgro, James Gosling

(See Collectors#joining.)

Joining is one of the less discussed but still wonderful new features of Java 8.

edited May 6, 2015 at 1:50

answered May 6, 2015 at 1:40

Radiodef

38k14 gold badges95 silver badges127 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Paul Boddington · Accepted Answer · 2015-05-06 01:03:33Z

12

Try this

Stream.of(names).map(Arrays::toString).forEach(System.out::println);

answered May 6, 2015 at 1:03

Paul Boddington

37.8k10 gold badges69 silver badges120 bronze badges

Comments

Reimeus · Accepted Answer · 2015-05-06 00:43:03Z

10

In standard Java

System.out.println(Arrays.deepToString(names));

answered May 6, 2015 at 0:43

Reimeus

160k16 gold badges225 silver badges282 bronze badges

1 Comment

MChaker Over a year ago

Very nice, but is there a new way using java 8 features?

drac_o · Accepted Answer · 2021-01-26 10:09:06Z

1

With Java 8 using Streams and forEach:

    Arrays.stream(names).forEach((i) -> {
        Arrays.stream(i).forEach((j) -> System.out.print(j + " "));
        System.out.println();
    });

The first forEach acts as outer loop while the next as inner loop.

This gives the following output:

Sam Smith 
Robert Delgro 
James Gosling

answered Jan 26, 2021 at 10:09

drac_o

4475 silver badges12 bronze badges

Collectives™ on Stack Overflow

How to Loop and Print 2D array using Java 8

4 Answers 4

Comments

Comments

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related