Arrays.deepToString() Method in Java - Quiz

The method public static String deepToString(Object[] a) from the java.util.Arrays class returns a string representation of a multidimensional array. It recursively walks through the nested arrays and wraps every nesting level in square brackets. It is the shortest way to print a 2D or multidimensional array to the console without writing loops.

Arrays.toString() processes only the first level of the array: each element is converted by calling its own toString(). For a 2D array the first-level elements are the nested arrays, and arrays do not override toString() — so you get the type and hash code, e.g. [[Ljava.lang.String;@1b6d3586, ...]. Arrays.deepToString() traverses the array recursively and prints the contents of every nesting level.

A one-dimensional int[] cannot be passed: the code will not compile because int[] is not convertible to Object[]. For one-dimensional primitive arrays there are Arrays.toString() overloads. An int[][], however, can be passed: its first-level elements are objects of type int[], so the array is compatible with the Object[] parameter, and the output looks like [[1, 2, 3], [4, 5, 6]].

If the argument is null, the method returns the string "null". Nested null elements are also printed as null. If the array directly or indirectly contains a reference to itself, "[...]" is printed in that place instead of infinite recursion — for example, [first, [...]].

For comparing and hashing multidimensional arrays, the Arrays class offers Arrays.deepEquals() and Arrays.deepHashCode(). Like deepToString(), they traverse all nesting levels recursively, unlike the "shallow" Arrays.equals() and Arrays.hashCode().