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

Alex Spurling picture Alex Spurling · Jan 3, 2009 · Viewed 2.4M times · Source

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]

Answer

Esko picture Esko · Jan 3, 2009

Since Java 5 you can import java.util.Arrays; and then 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 ]