Java tutorial – 2 data types

Java Data Types

Primitive Data Type 

In Java, there are two types of data types: Primitive data type and Non-primitive data type. 

Primitive Data Types: These are the built-in data types in Java.

1.    – byte : 8-bit signed integer. It has a minimum value of -128 and a maximum value of 127 (inclusive).
2.    – short : 16-bit signed integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive).
3.    – int : 32-bit signed integer. It has a minimum value of -2,147,483,648 and a maximum value of 2,147,483,647 (inclusive).
4.    – long: 64-bit signed integer. It has a minimum value of -9,223,372,036,854,775,808 and a maximum value of 9,223,372,036,854,775,807 (inclusive).
5.    – float: Single-precision 32-bit IEEE 754 floating point.
6.    – `double`: Double-precision 64-bit IEEE 754 floating point.
7.    – boolean: The boolean data type has only two possible values: true and false.
8.    – `char`: Single 16-bit Unicode character. It has a minimum value of ‘\u0000’ (or 0) and a maximum value of ‘\uffff’ (or 65,535 inclusive).

Data Type	Size(in byte)	Description
byte	1	-2^7 to 2^7-1, -128 to 127
short	2	-2^15 to 2^15-1, -32,768 to 32,767
int	4	-2,147,483,648 to 2,147,483,647
long	8	-2^63 to 2^63-1, -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
float	4	Sufficient for storing 6 to 7 decimal digits
double	8	Sufficient for storing 15 decimal digits
boolean	1	Stores true or false values
char	2	Stores a single character/letter or ASCII values

Declaration of Primitive Data Types and Assign Values  in Java:

byte x = 10; 
short num1=10;
int myNum = 5;               
float myFloatNum = 5.99f;    
double myDoubleNum = 5.5;
boolean myBool = true;       
char myLetter = 'D';   

Non-Primitive Data Type

Non-Primitive Data Types (Reference Data Types, or reference types): These are created by the programmer and are not defined by Java (except for String). Non-primitive types can be used to call methods to perform certain operations, while primitive types cannot. Examples of non-primitive types are:

   – String: The most commonly used non-primitive data type. It represents a sequence of characters.

   – Arrays: A group of like-typed variables that are referred to by a common name.

   – Classes: A class is a blueprint from which individual objects are created.

   – `Interfaces`: Like a class, an interface can have methods and variables, but the methods declared in an interface are by default abstract (only method signature, no body).

   – Enum: A special data type that enables for a variable to be a set of predefined constants. The variable must be equal to one of the values that have been predefined for it.

String myText = "Hello";     // String
String[] array = new String[100]; // Array

// Interface
interface Animal {
public void animalSound(); // interface method (does not have a body)
public void sleep();
}

// Enumerate typeenum Level {
  LOW,
  MEDIUM,
  HIGH
}

Note: Java is statically typed. That means each variable must be declared with a data type before it can be used.

Differences Between Two Data Types

The main difference between primitive and non-primitive data types are:

• Primitive types are predefined (already defined) in Java. Non-primitive types are created by the programmer and are not defined by Java (except for String).
• Non-primitive types can be used to call methods to perform certain operations, while primitive types cannot.
• A primitive type has always a value, while non-primitive types can be null.
• A primitive type starts with a lowercase letter, while non-primitive type starts with an uppercase letter.
• The size of a primitive type depends on the data type, while non-primitive types have all the same size.

Java Wrapper Classes

Wrapper classes provide a way to use primitive data types (int, boolean, etc..) as objects.

The table below shows the primitive type and the equivalent wrapper class:

Primitive Data Type	Wrapper Class
byte	Byte
short	Short
int	Integer
long	Long
float	Float
double	Double
boolean	Boolean
char	Character

Pass-by-reference and Pass-by-value

• Pass-by-reference: When a method is called, the method arguments reference the same variable in memory as the caller. 
• Pass-by-value: When a method is called, the caller passes a copy of the argument variables to the method resulting in two values in memory.

Java is always pass-by-value. The reason this is confusing is that Java achieves its functionality using special variable types known as object references. 

Reference: https://sentry.io/answers/java-pass-by-reference-or-value/ 

Header image from: https://getkt.com/blog/reintroduction-to-java-data-types/