How to print two dimensional array of strings as String

Question

I know how to do the toString method for one dimensional arrays of strings, but how do I print a two dimensional array? With 1D I do it this way:

public String toString() {
    StringBuffer result = new StringBuffer();
    res = this.magnitude;

    String separator = "";
    if (res.length > 0) {
        result.append(res[0]);
        for (int i=1; i<res.length; i++) {
            result.append(separator);
            result.append(res[i]);
        }
    }
return result.toString();

How can I print a 2D array?

If you are in a single-threaded environment, the StringBuilder class should generally be used in preference to StringBuffer as it supports all of the same operations but it is faster, as it performs no synchronization. — Desintegr
– Desintegr, Commented Mar 7, 2010 at 19:23

Robert Christie · Accepted Answer · 2010-03-07 20:16:38Z

79

The Arrays class defines a couple of useful methods

Arrays.toString - which doesn't work for nested arrays
Arrays.deepToString - which does exactly what you want

String[][] aastr = {{"hello", "world"},{"Goodbye", "planet"}};
System.out.println(Arrays.deepToString(aastr));

Gives

  [[hello, world], [Goodbye, planet]]

edited Mar 7, 2010 at 20:16

answered Mar 7, 2010 at 19:32

Robert Christie

20.7k8 gold badges45 silver badges38 bronze badges

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

1 Comment

Ojonugwa Jude Ochalifu Over a year ago

10 years and I never heard of deepToString. Facepalm

Jack · Accepted Answer · 2010-03-07 19:21:06Z

6

You just iterate twice over the elements:

StringBuffer results = new StringBuffer();
String separator = ","
float[][] values = new float[50][50];

// init values

for (int i = 0; i < values.length; ++i)
{
  result.append('[');
  for (int j = 0; j < values[i].length; ++j)
    if (j > 0)
      result.append(values[i][j]);
    else
      result.append(values[i][j]).append(separator);
  result.append(']');
}

IMPORTANT: StringBuffer are also useful because you can chain operations, eg: buffer.append(..).append(..).append(..) since it returns a reference to self! Use synctactic sugar when available..

IMPORTANT2: since in this case you plan to append many things to the StringBuffer it's good to estimate a capacity to avoid allocating and relocating the array many times during appends, you can do it calculating the size of the multi dimensional array multiplied by the average character length of the element you plan to append.

answered Mar 7, 2010 at 19:21

Jack

134k33 gold badges252 silver badges349 bronze badges

3 Comments

polygenelubricants Over a year ago

Method chaining has nothing to do with syntactic sugar; it's an API feature, not a language feature. Otherwise, +1.

Karussell Over a year ago

you could use StringBuilder which is not synchronized and could be faster under some circumstances

Jack Over a year ago

Yep, I knew about it. Synctactic sugar should regard the syntax (grammar) of the language while this is just a method of the class.. but no other term came into my mind, see it as a poetic license :)

Pindatjuh · Accepted Answer · 2010-03-07 20:00:15Z

2

public static <T> String to2DString(T[][] x) {
    final String vSep = "\n";
    final String hSep = ", ";
    final StringBuilder sb = new StringBuilder();

    if(x != null)
    for(int i = 0; i < x.length; i++) {
        final T[] a = x[i];
        if(i > 0) {
            sb.append(vSep);
        }
        if(a != null)
        for(int j = 0; j < a.length; j++) {
            final T b = a[j];
            if(j > 0) {
                sb.append(hSep);
            }
            sb.append(b);
        }
    }
    return sb.toString();
}

edited Mar 7, 2010 at 20:00

answered Mar 7, 2010 at 19:24

Pindatjuh

10.6k1 gold badge45 silver badges69 bronze badges

1 Comment

polygenelubricants Over a year ago

This is problematic if the array contains multiple references that are ==. For example, it wouldn't work with new String[][] {{"1", "1"}, {"1", "1"}} because of interning. Bad technique, in my opinion.

Felix Kling · Accepted Answer · 2010-03-07 19:20:26Z

0

Two for loops:

for (int i=1; i<res.length; i++) {
    for (int j=1; j<res[i].length; j++) {
        result.append(separator);
        result.append(res[i][j]);
    }
}

answered Mar 7, 2010 at 19:20

Felix Kling

820k181 gold badges1.1k silver badges1.2k bronze badges

Comments

Sil · Accepted Answer · 2019-04-11 19:11:12Z

0

public static void main(String[] args) {

    String array [] [] = {
        {"*","*", "*", "*", "*", "*"},
        {"*"},
        {"*"},
        {"*"},
        {"*","*", "*", "*", "*", "*"},
        {"*"},
        {"*"},
        {"*"},
        {"*"},
        {"*"}};


    for (int row=0; row<array.length;row++) {

        for (int column = 0; column < array[row].length; column++) {
            System.out.print(array[row][column]);
        }
        System.out.println();
    }
}

answered Apr 11, 2019 at 19:11

Sil

1

Collectives™ on Stack Overflow

How to print two dimensional array of strings as String

5 Answers 5

1 Comment

3 Comments

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

1 Comment

3 Comments

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest