Home » Java » What's the simplest way to print a Java array?

What's the simplest way to print a Java array?

Posted by: admin November 14, 2021 Leave a comment

Questions:

In Java, arrays don’t override toString(), so if you try to print one directly, you get the className + ‘@’ + the hex of the hashCode of the array, as defined by Object.toString():

int[] intArray = new int[] {1, 2, 3, 4, 5};
System.out.println(intArray);     // prints something like '[[email protected]'

But usually, we’d actually want something more like [1, 2, 3, 4, 5]. What’s the simplest way of doing that? Here are some example inputs and outputs:

// Array of primitives:
int[] intArray = new int[] {1, 2, 3, 4, 5};
//output: [1, 2, 3, 4, 5]

// Array of object references:
String[] strArray = new String[] {"John", "Mary", "Bob"};
//output: [John, Mary, Bob]

Answers:

Since Java 5 you can use Arrays.toString(arr) or Arrays.deepToString(arr) for arrays within arrays. Note that the Object[] version calls .toString() on each object in the array. The output is even decorated in the exact way you’re asking.

Examples:

  • Simple Array:

    String[] array = new String[] {"John", "Mary", "Bob"};
    System.out.println(Arrays.toString(array));
    

    Output:

    [John, Mary, Bob]
    
  • Nested Array:

    String[][] deepArray = new String[][] {{"John", "Mary"}, {"Alice", "Bob"}};
    System.out.println(Arrays.toString(deepArray));
    //output: [[Ljava.lang.String;@106d69c, [Ljava.lang.String;@52e922]
    System.out.println(Arrays.deepToString(deepArray));
    

    Output:

    [[John, Mary], [Alice, Bob]]
    
  • double Array:

    double[] doubleArray = { 7.0, 9.0, 5.0, 1.0, 3.0 };
    System.out.println(Arrays.toString(doubleArray));
    

    Output:

    [7.0, 9.0, 5.0, 1.0, 3.0 ]
    
  • int Array:

    int[] intArray = { 7, 9, 5, 1, 3 };
    System.out.println(Arrays.toString(intArray));
    

    Output:

    [7, 9, 5, 1, 3 ]
    

###

Always check the standard libraries first.

import java.util.Arrays;

Then try:

System.out.println(Arrays.toString(array));

or if your array contains other arrays as elements:

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

###

This is nice to know, however, as for “always check the standard libraries first” I’d never have stumbled upon the trick of Arrays.toString( myarray )

–since I was concentrating on the type of myarray to see how to do this. I didn’t want to have to iterate through the thing: I wanted an easy call to make it come out similar to what I see in the Eclipse debugger and myarray.toString() just wasn’t doing it.

import java.util.Arrays;
.
.
.
System.out.println( Arrays.toString( myarray ) );

###

In JDK1.8 you can use aggregate operations and a lambda expression:

String[] strArray = new String[] {"John", "Mary", "Bob"};

// #1
Arrays.asList(strArray).stream().forEach(s -> System.out.println(s));

// #2
Stream.of(strArray).forEach(System.out::println);

// #3
Arrays.stream(strArray).forEach(System.out::println);

/* output:
John
Mary
Bob
*/

###

Starting with Java 8, one could also take advantage of the join() method provided by the String class to print out array elements, without the brackets, and separated by a delimiter of choice (which is the space character for the example shown below):

String[] greeting = {"Hey", "there", "amigo!"};
String delimiter = " ";
String.join(delimiter, greeting) 

The output will be “Hey there amigo!”.

###

Prior to Java 8

We could have used Arrays.toString(array) to print one dimensional array and Arrays.deepToString(array) for multi-dimensional arrays.

Java 8

Now we have got the option of Stream and lambda to print the array.

Printing One dimensional Array:

public static void main(String[] args) {
    int[] intArray = new int[] {1, 2, 3, 4, 5};
    String[] strArray = new String[] {"John", "Mary", "Bob"};

    //Prior to Java 8
    System.out.println(Arrays.toString(intArray));
    System.out.println(Arrays.toString(strArray));

    // In Java 8 we have lambda expressions
    Arrays.stream(intArray).forEach(System.out::println);
    Arrays.stream(strArray).forEach(System.out::println);
}

The output is:

[1, 2, 3, 4, 5] [John, Mary, Bob] 1
2
3
4
5
John
Mary
Bob

Printing Multi-dimensional Array
Just in case we want to print multi-dimensional array we can use Arrays.deepToString(array) as:

public static void main(String[] args) {
    int[][] int2DArray = new int[][] { {11, 12}, { 21, 22}, {31, 32, 33} };
    String[][] str2DArray = new String[][]{ {"John", "Bravo"} , {"Mary", "Lee"}, {"Bob", "Johnson"} };

    //Prior to Java 8
    System.out.println(Arrays.deepToString(int2DArray));
    System.out.println(Arrays.deepToString(str2DArray));

    // In Java 8 we have lambda expressions
    Arrays.stream(int2DArray).flatMapToInt(x -> Arrays.stream(x)).forEach(System.out::println);
    Arrays.stream(str2DArray).flatMap(x -> Arrays.stream(x)).forEach(System.out::println);
} 

Now the point to observe is that the method Arrays.stream(T[]), which in case of int[] returns us Stream<int[]> and then method flatMapToInt() maps each element of stream with the contents of a mapped stream produced by applying the provided mapping function to each element.

The output is:

[[11, 12], [21, 22], [31, 32, 33]] [[John, Bravo], [Mary, Lee], [Bob, Johnson]] 11
12
21
22
31
32
33
John
Bravo
Mary
Lee
Bob
Johnson

###

If you’re using Java 1.4, you can instead do:

System.out.println(Arrays.asList(array));

(This works in 1.5+ too, of course.)

###

Arrays.toString

As a direct answer, the solution provided by several, including @Esko, using the Arrays.toString and Arrays.deepToString methods, is simply the best.

Java 8 – Stream.collect(joining()), Stream.forEach

Below I try to list some of the other methods suggested, attempting to improve a little, with the most notable addition being the use of the Stream.collect operator, using a joining Collector, to mimic what the String.join is doing.

int[] ints = new int[] {1, 2, 3, 4, 5};
System.out.println(IntStream.of(ints).mapToObj(Integer::toString).collect(Collectors.joining(", ")));
System.out.println(IntStream.of(ints).boxed().map(Object::toString).collect(Collectors.joining(", ")));
System.out.println(Arrays.toString(ints));

String[] strs = new String[] {"John", "Mary", "Bob"};
System.out.println(Stream.of(strs).collect(Collectors.joining(", ")));
System.out.println(String.join(", ", strs));
System.out.println(Arrays.toString(strs));

DayOfWeek [] days = { FRIDAY, MONDAY, TUESDAY };
System.out.println(Stream.of(days).map(Object::toString).collect(Collectors.joining(", ")));
System.out.println(Arrays.toString(days));

// These options are not the same as each item is printed on a new line:
IntStream.of(ints).forEach(System.out::println);
Stream.of(strs).forEach(System.out::println);
Stream.of(days).forEach(System.out::println);

###

Arrays.deepToString(arr) only prints on one line.

int[][] table = new int[2][2];

To actually get a table to print as a two dimensional table, I had to do this:

System.out.println(Arrays.deepToString(table).replaceAll("],", "]," + System.getProperty("line.separator")));

It seems like the Arrays.deepToString(arr) method should take a separator string, but unfortunately it doesn’t.

###

for(int n: someArray) {
    System.out.println(n+" ");
}

###

Different Ways to Print Arrays in Java:

  1. Simple Way

    List<String> list = new ArrayList<String>();
    list.add("One");
    list.add("Two");
    list.add("Three");
    list.add("Four");
    // Print the list in console
    System.out.println(list);
    

Output:
[One, Two, Three, Four]

  1. Using toString()

    String[] array = new String[] { "One", "Two", "Three", "Four" };
    System.out.println(Arrays.toString(array));
    

Output: [One, Two, Three, Four]

  1. Printing Array of Arrays

    String[] arr1 = new String[] { "Fifth", "Sixth" };
    String[] arr2 = new String[] { "Seventh", "Eight" };
    String[][] arrayOfArray = new String[][] { arr1, arr2 };
    System.out.println(arrayOfArray);
    System.out.println(Arrays.toString(arrayOfArray));
    System.out.println(Arrays.deepToString(arrayOfArray));
    

Output: [[Ljava.lang.String;@1ad086a [[Ljava.lang.String;@10385c1,
[Ljava.lang.String;@42719c] [[Fifth, Sixth], [Seventh, Eighth]]

Resource: Access An Array

###

Using regular for loop is the simplest way of printing array in my opinion.
Here you have a sample code based on your intArray

for (int i = 0; i < intArray.length; i++) {
   System.out.print(intArray[i] + ", ");
}

It gives output as yours
1, 2, 3, 4, 5

###

It should always work whichever JDK version you use:

System.out.println(Arrays.asList(array));

It will work if the Array contains Objects. If the Array contains primitive types, you can use wrapper classes instead storing the primitive directly as..

Example:

int[] a = new int[]{1,2,3,4,5};

Replace it with:

Integer[] a = new Integer[]{1,2,3,4,5};

Update :

Yes ! this is to be mention that converting an array to an object array OR to use the Object’s array is costly and may slow the execution. it happens by the nature of java called autoboxing.

So only for printing purpose, It should not be used. we can make a function which takes an array as parameter and prints the desired format as

public void printArray(int [] a){
        //write printing code
} 

###

I came across this post in Vanilla #Java recently. It’s not very convenient writing Arrays.toString(arr);, then importing java.util.Arrays; all the time.

Please note, this is not a permanent fix by any means. Just a hack that can make debugging simpler.

Printing an array directly gives the internal representation and the hashCode. Now, all classes have Object as the parent-type. So, why not hack the Object.toString()? Without modification, the Object class looks like this:

public String toString() {
    return getClass().getName() + "@" + Integer.toHexString(hashCode());
}

What if this is changed to:

public String toString() {
    if (this instanceof boolean[])
        return Arrays.toString((boolean[]) this);
    if (this instanceof byte[])
        return Arrays.toString((byte[]) this);
    if (this instanceof short[])
        return Arrays.toString((short[]) this);
    if (this instanceof char[])
        return Arrays.toString((char[]) this);
    if (this instanceof int[])
        return Arrays.toString((int[]) this);
    if (this instanceof long[])
        return Arrays.toString((long[]) this);
    if (this instanceof float[])
        return Arrays.toString((float[]) this);
    if (this instanceof double[])
        return Arrays.toString((double[]) this);
    if (this instanceof Object[])
        return Arrays.deepToString((Object[]) this);
    return getClass().getName() + "@" + Integer.toHexString(hashCode());
}

This modded class may simply be added to the class path by adding the following to the command line: -Xbootclasspath/p:target/classes.

Now, with the availability of deepToString(..) since Java 5, the toString(..) can easily be changed to deepToString(..) to add support for arrays that contain other arrays.

I found this to be a quite useful hack and it would be great if Java could simply add this. I understand potential issues with having very large arrays since the string representations could be problematic. Maybe pass something like a System.outor a PrintWriter for such eventualities.

###

In java 8 it is easy. there are two keywords

  1. stream: Arrays.stream(intArray).forEach
  2. method reference: ::println

    int[] intArray = new int[] {1, 2, 3, 4, 5};
    Arrays.stream(intArray).forEach(System.out::println);
    

If you want to print all elements in the array in the same line, then just use print instead of println i.e.

int[] intArray = new int[] {1, 2, 3, 4, 5};
Arrays.stream(intArray).forEach(System.out::print);

Another way without method reference just use:

int[] intArray = new int[] {1, 2, 3, 4, 5};
System.out.println(Arrays.toString(intArray));

###

You could loop through the array, printing out each item, as you loop. For example:

String[] items = {"item 1", "item 2", "item 3"};

for(int i = 0; i < items.length; i++) {

    System.out.println(items[i]);

}

Output:

item 1
item 2
item 3

###

There Are Following way to print Array

 // 1) toString()  
    int[] arrayInt = new int[] {10, 20, 30, 40, 50};  
    System.out.println(Arrays.toString(arrayInt));

// 2 for loop()
    for (int number : arrayInt) {
        System.out.println(number);
    }

// 3 for each()
    for(int x: arrayInt){
         System.out.println(x);
     }

###

There’s one additional way if your array is of type char[]:

char A[] = {'a', 'b', 'c'}; 

System.out.println(A); // no other arguments

prints

abc

###

A simplified shortcut I’ve tried is this:

    int x[] = {1,2,3};
    String printableText = Arrays.toString(x).replaceAll("[\[\]]", "").replaceAll(", ", "\n");
    System.out.println(printableText);

It will print

1
2
3

No loops required in this approach and it is best for small arrays only

###

Using org.apache.commons.lang3.StringUtils.join(*) methods can be an option
For example:

String[] strArray = new String[] { "John", "Mary", "Bob" };
String arrayAsCSV = StringUtils.join(strArray, " , ");
System.out.printf("[%s]", arrayAsCSV);
//output: [John , Mary , Bob]

I used the following dependency

<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.3.2</version>

###

For-each loop can also be used to print elements of array:

int array[] = {1, 2, 3, 4, 5};
for (int i:array)
    System.out.println(i);

###

To add to all the answers, printing the object as a JSON string is also an option.

Using Jackson:

ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
System.out.println(ow.writeValueAsString(anyArray));

Using Gson:

Gson gson = new Gson();
System.out.println(gson.toJson(anyArray));

###

// array of primitives:
int[] intArray = new int[] {1, 2, 3, 4, 5};

System.out.println(Arrays.toString(intArray));

output: [1, 2, 3, 4, 5]

// array of object references:
String[] strArray = new String[] {"John", "Mary", "Bob"};

System.out.println(Arrays.toString(strArray));

output: [John, Mary, Bob]

###

public class printer {

    public static void main(String[] args) {
        String a[] = new String[4];
        Scanner sc = new Scanner(System.in);
        System.out.println("enter the data");
        for (int i = 0; i < 4; i++) {
            a[i] = sc.nextLine();
        }
        System.out.println("the entered data is");
        for (String i : a) {
            System.out.println(i);
        }
      }
    }

###

This is marked as a duplicate for printing a byte[]. Note: for a byte array there are additional methods which may be appropriate.

You can print it as a String if it contains ISO-8859-1 chars.

String s = new String(bytes, StandardChars.ISO_8559);
System.out.println(s);
// to reverse
byte[] bytes2 = s.getBytes(StandardChars.ISO_8559);

or if it contains a UTF-8 string

String s = new String(bytes, StandardChars.UTF_8);
System.out.println(s);
// to reverse
byte[] bytes2 = s.getBytes(StandardChars.UTF_8);

or if you want print it as hexadecimal.

String s = DatatypeConverter.printHexBinary(bytes);
System.out.println(s);
// to reverse
byte[] bytes2 = DatatypeConverter.parseHexBinary(s);

or if you want print it as base64.

String s = DatatypeConverter.printBase64Binary(bytes);
System.out.println(s);
// to reverse
byte[] bytes2 = DatatypeConverter.parseBase64Binary(s);

or if you want to print an array of signed byte values

String s = Arrays.toString(bytes);
System.out.println(s);
// to reverse
String[] split = s.substring(1, s.length() - 1).split(", ");
byte[] bytes2 = new byte[split.length];
for (int i = 0; i < bytes2.length; i++)
    bytes2[i] = Byte.parseByte(split[i]);

or if you want to print an array of unsigned byte values

String s = Arrays.toString(
               IntStream.range(0, bytes.length).map(i -> bytes[i] & 0xFF).toArray());
System.out.println(s);
// to reverse
String[] split = s.substring(1, s.length() - 1).split(", ");
byte[] bytes2 = new byte[split.length];
for (int i = 0; i < bytes2.length; i++)
    bytes2[i] = (byte) Integer.parseInt(split[i]); // might need a range check.

###

if you are running jdk 8.

public static void print(int[] array) {
    StringJoiner joiner = new StringJoiner(",", "[", "]");
    Arrays.stream(array).forEach(element -> joiner.add(element + ""));
    System.out.println(joiner.toString());
}


int[] array = new int[]{7, 3, 5, 1, 3};
print(array);

output:

[7,3,5,1,3]

###

Here a possible printing function:

  public static void printArray (int [] array){
        System.out.print("{ ");
        for (int i = 0; i < array.length; i++){
            System.out.print("[" + array[i] + "] ");
        }
        System.out.print("}");
    }

For example, if main is like this

public static void main (String [] args){
    int [] array = {1, 2, 3, 4};
    printArray(array);
}

the output will be { [1] [2] [3] [4] }

###

In java 8 :

Arrays.stream(myArray).forEach(System.out::println);

###

If using Commons.Lang library, we could do:

ArrayUtils.toString(array)

int[] intArray = new int[] {1, 2, 3, 4, 5};
String[] strArray = new String[] {"John", "Mary", "Bob"};
ArrayUtils.toString(intArray);
ArrayUtils.toString(strArray);

Output:

{1,2,3,4,5}
{John,Mary,Bob}

###

In JDK1.8 you can use aggregate operations and a lambda expression:

String[] strArray = new String[] {"John", "Mary", "Bob"};

// #1
Arrays.asList(strArray).stream().forEach(s -> System.out.println(s));

// #2
Stream.of(strArray).forEach(System.out::println);

// #3
Arrays.stream(strArray).forEach(System.out::println);

/* output:
John
Mary
Bob
*/

Also, starting with Java 8, one could also take advantage of the join() method provided by the String class to print out array elements, without the brackets, and separated by a delimiter of choice (which is the space character for the example shown below)

string[] greeting = {"Hey", "there", "amigo!"};
String delimiter = " ";
String.join(delimiter, greeting) 

`
The output will be “Hey there amigo!”

Tags: