Primitive and Reference types

Data types in Java

There are mainly 2 groups of data types in Java as Primitive and Reference data types.

Java has 8 primitives types built-in. All are lowercase. E.g: int

int age = 23

All 8 primitive types,

• boolean
• byte
• short
• char
• int
• long
• float
• double

Reference types are huge and constantly growing. There are built-in types once and also the programmer can create its own.

Simply all data types other than primitive are reference...

E.g: String, Scanner, Thread, File

String language = new String(“texthere”);

In most cases, new keyword is used to instantiate (create) a reference type (object).

User-defined ones will be like,

Person person = new Person();

Stack Vs Heap

The main difference comes related to this. There are 2 memory spaces as stack and heap. Primitive types store actual values and reference types stores memory address where actual data is located.

More details about stack vs heap [1]

Referencing

Here is a small example to differentiate the use of existing memory address and creating a memory address.

String x = new String(“text”);
 
String y = new String(“text”);
String z = y;
 
System.out.println(x == y); // false, because its 2 memory addresses
System.out.println(y == z); // true, referring same memory address

Null

Unlike primitive types, reference type can refer to a null.

String x = null

References

[1]https://stackoverflow.com/questions/79923/what-and-where-are-the-stack-and-heap