03_arrays_of_primitive_types.md

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Arrays of primitive types

Array Definition

• An array of a primitive type is sequence of the primitive type that is referenced as a single variable

Indexing into an Array

• Example
  • If intValues is an array of size 10 of type int, then the name intValues can be used to reference all 10 int values associated with the array intValues, with intValues[0] being the first element of the array, intValues[1] the second, ..., and intValues[9] being the 10th value

Array declaration and intialization

• To declare intValues as an array:

 int[] intValues;

• To specify intValues size (allocate memory versus define as an array)

int[] intValues = new int[10];

• Alternatives are

int intValues1[] = new int[10]; // originally for C compatability
int[] intValues2;
intValues2 = new int[10];
int[] intValues4 = {0,1,2,3,4,5,6,7,8,9};
int[] intValues3 = new int[]{0,1,2,3,4,5,6,7,8,9};
// the last form can be used to completely reassign an array variable:
intValues4 = new int[]{5,3,2,1};

Default Values

• Java arrays of primitive values are in initialized to their default value
  • 0 for integer types, 0.0 for float types, and false for boolean types

Array Allocation

• Java arrays of primitives are allocated in heap memory

Multi Dimensional Arrays

• Arrays can have multiple dimensions

int[][][] intValues = new int[10][20][30];

• intValues.length = 10

• intValues[0].length = 20

• intValues[0][0].length = 30

• Note that accessing an element in a 3 dimensional array has the form intValues[7][13][10], where 0<=7<=10, 0<=13<=20, 0<=10<=30.

Empty Arrays

• Arrays can have length 0, meaning they are empty:

int[] intValues = new int[0]; // is valid

Jagged Arrays

• The following are also valid:

int[][] v = new int[3][];
v[0] = new int[10];
v[1] = new int[20];
v[2] = new int[30];

• v.length = 3
• v[0].length = 10
• v[1].length = 20
• v[2].length = 30
• We call v a jagged array.

Other primitive type arrays

• There can also be arrays of primitive values utilizing boolean, byte, short, char, long, float,double