What's the Simplest Way to Print a Java Array?

Robert Thorne
Robert Thorne
• • 13 min read

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...

What's the Simplest Way to Print a Java Array?

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 '[I@3343c8b3'

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]
7

35 Answers

1
2

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 ]
8

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));
1

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 ) );
0

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
*/
0

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!".

Must Read

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.

Robert Thorne

Robert Thorne

Automotive & Future Transportation Editor
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Robert Thorne covers electric vehicle innovations, autonomous driving systems, global mobility trends, and automotive engineering developments.