# Constructing an array

• This step creates an actual array object on the heap memory with the specified size i.e.) number of elements this array will hold.
• Size must be a positive integer value.
• This is done using new keyword/operator.
• This step is also known as instantiating an array, creating an array object, allocating memory space.

## One dimensional array

```double[] studentAvgs; //declaring an array reference
studentAvgs = new double[5]; //creating an array object or allocates memory for 5 elements
```

The preceding code creates a new array object on the heap holding five elements – with each element being a double with a default value 0.0

You can also declare and instantiate in a single statement.

```double[] studentAvgs = new double[5]; //declare & allocate an array object
```

for example, the fifth element would be accessed at index 4.

## Multidimensional array

A two dimensional array is simply an array object with each element in the array being a reference to another array.
Method 1:

```double[][] studentAvgs; //declaring an array reference
studentAvgs = new double[3][]; //creating an array object
```

You can also declare and instantiate a two dimensional array in a single statement.

` double[][] studentAvgs = new double[3][];`

Method 1 creates three rows and each row can hold any number of elements which can be defined later.

Method 2:

```double[][] studentAvgs; //declaring an array reference
studentAvgs = new double[3][2]; //creating an array object
```

You can also declare and instantiate a two dimensional array in a single statement.

` double[][] studentAvgs = new double[3][2];`

Method 2 creates three rows and each row referring to an array of two elements.

When creating a two dimensional array, you must provide row size.
double[][] studentAvgs = new double[][]; //ERROR

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