Nonprimitive Data Types in Java

Nonprimitive data types in Java are reference variables (object references), arrays and enums. All nonprimitive data types are references to memory where the objects live.

[objects]

References provide access to objects. The declaration syntax is just the same as with primitives.

Decryptor decryptor;

The above example shows that we are creating a reference to a Decryptor object. Take note that no real object is created yet.

The object is created through the new operator.

decryptor = new Decryptor();

The reference decryptor now points to a Decryptor object in the heap.

[arrays]

Arrays are objects used to hold a collection of primitive or nonprimitive data of the same type. Take note that even if an array holds primitive data, it is always an object.

Steps for creating an array:

1. Declaration of an array variable (reference)

char[] charArray; //or
char charArray[];

2. Instantiation of an array of a certain size

charArray = new char[8];

3. Initialization of each array element.

charArray[0] = 'k';
charArray[1] = 'a';
charArray[2] = 'r';
charArray[3] = 'e';
charArray[4] = 'n';
charArray[5] = 'e';
charArray[6] = 'v';
charArray[7] = 'e';

Once a size is given to an array, it cannot be changed later.

[enums]

The data type enum is used to store a predetermined set of values or constants. Examples are the months in a year, the days in a week, etc.

Steps for creating an enum:

1. Define the enum type with unique named values

enum ShortWeek {MON, TUE, WED, THU, FRI, SAT, SUN};

2. Assign a reference to the enum type

ShortWeek monday = ShortWeek.MON;

You can only create X instances of an enum type, where X is the number of elements that the enum type holds.