Question

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] 

Answer 1

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"}}; // Gives undesired output: System.out.println(Arrays.toString(deepArray)); // Gives the desired output: System.out.println(Arrays.deepToString(deepArray)); 

  Output:

  [[Ljava.lang.String;@106d69c, [Ljava.lang.String;@52e922] [[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 ]