How to Declare a Multidimensional Array in Java Without Specifying the Inner Array Size?

Question

How do you declare a multidimensional array in Java without indicating the size of the inner array?

int[][] myArray = new int[10][]; // Declare a 2D array with 10 rows and unspecified columns.

Answer

In Java, it is possible to declare a multidimensional array without specifying the size of the inner arrays. This allows flexibility in initializing each row with different lengths later on.

int[][] myArray = new int[10][];
myArray[0] = new int[5];  // Initialize first inner array
myArray[1] = new int[3];  // Initialize second inner array
myArray[2] = new int[7];  // Initialize third inner array // Implies creating 3rd row with 7 columns.

Causes

  • You might want to initialize the outer array with a fixed size but require different lengths for each inner array.
  • Flexibility in cases where the inner array size is determined at runtime.

Solutions

  • To declare such an array, use the syntax `new int[outerSize][]`. For example, `int[][] myArray = new int[10][];` creates an array with 10 rows where the size of each inner array remains uninitialized until assigned.
  • After declaration, you can individually initialize the inner arrays, e.g., `myArray[0] = new int[5]; // First row with 5 columns myArray[1] = new int[8]; // Second row with 8 columns`.

Common Mistakes

Mistake: Attempting to access elements in uninitialized inner arrays.

Solution: Always initialize inner arrays before accessing elements, for example: `if (myArray[0] != null) { int element = myArray[0][0]; }`.

Mistake: Confusing the syntax of multidimensional arrays with arrays of objects.

Solution: Remember that in Java, arrays are reference types; each inner array reference must be initialized individually.

Helpers

  • Java multidimensional array
  • Declare array without size in Java
  • Java array initialization
  • Java 2D array without size

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