Java Variables and Literals

Java Variables

A variable is a location in memory (storage area) to hold data.

To indicate the storage area, each variable should be given a unique name (identifier). Learn more about Java identifiers.

Create Variables in Java

Here's how we create a variable in Java,

int speedLimit = 80;

Here, speedLimit is a variable of int data type and we have assigned value 80 to it.

The int data type suggests that the variable can only hold integers. To learn more, visit Java data types.

In the example, we have assigned value to the variable during declaration. However, it's not mandatory.

You can declare variables and assign variables separately. For example,

int speedLimit;
speedLimit = 80;

Note: Java is a statically-typed language. It means that all variables must be declared before they can be used.

Change values of variables

The value of a variable can be changed in the program, hence the name variable. For example,

int speedLimit = 80;
... .. ...
speedLimit = 90; 

Here, initially, the value of speedLimit is 80. Later, we changed it to 90.

However, we cannot change the data type of a variable in Java within the same scope.

What is the variable scope?

Don't worry about it for now. Just remember that we can't do something like this:

int speedLimit = 80;
... .. ...
float speedLimit;

To learn more, visit: Can I change declaration type for a variable in Java?

Rules for Naming Variables in Java

Java programming language has its own set of rules and conventions for naming variables. Here's what you need to know:

• Java is case sensitive. Hence, age and AGE are two different variables. For example,
   

  int age = 24;
  int AGE = 25;
  
  System.out.println(age);  // prints 24
  System.out.println(AGE);  // prints 25

• Variables must start with either a letter or an underscore, _ or a dollar, $ sign. For example,
   

  int age;  // valid name and good practice
  int _age;  // valid but bad practice
  int $age;  // valid but bad practice

• Variable names cannot start with numbers. For example,
   

  int 1age;  // invalid variables

• Variable names can't use whitespace. For example,
   

  int my age;  // invalid variables

  
  
  Here, is we need to use variable names having more than one word, use all lowercase letters for the first word and capitalize the first letter of each subsequent word. For example, myAge.
• When creating variables, choose a name that makes sense. For example, score, number, level makes more sense than variable names such as s, n, and l.
• If you choose one-word variable names, use all lowercase letters. For example, it's better to use speed rather than SPEED, or sPEED.

There are 4 types of variables in Java programming language:

• Instance Variables (Non-Static Fields)
• Class Variables (Static Fields)
• Local Variables
• Parameters

If you are interested to learn more about it now, visit Java Variable Types.

Java literals

Literals are data used for representing fixed values. They can be used directly in the code. For example,

int a = 1;
float b = 2.5;
char c = 'F';

Here, 1, 2.5, and 'F' are literals.

Here are different types of literals in Java.

1. Boolean Literals

In Java, boolean literals are used to initialize boolean data types. They can store two values: true and false. For example,

boolean flag1 = false;
boolean flag2 = true;

Here, false and true are two boolean literals.

2. Integer Literals

An integer literal is a numeric value(associated with numbers) without any fractional or exponential part. There are 4 types of integer literals in Java:

1. binary (base 2)
2. decimal (base 10)
3. octal (base 8)
4. hexadecimal (base 16)

For example:

// binary
int binaryNumber = 0b10010;
// octal 
int octalNumber = 027;

// decimal
int decNumber = 34;

// hexadecimal 
int hexNumber = 0x2F; // 0x represents hexadecimal
// binary
int binNumber = 0b10010; // 0b represents binary

In Java, binary starts with 0b, octal starts with 0, and hexadecimal starts with 0x.

Note: Integer literals are used to initialize variables of integer types like byte, short, int, and long.

3. Floating-point Literals

A floating-point literal is a numeric literal that has either a fractional form or an exponential form. For example,

class Main {
  public static void main(String[] args) {
    	
    double myDouble = 3.4;
    float myFloat = 3.4F;
 
    // 3.445*10^2
    double myDoubleScientific = 3.445e2;

    System.out.println(myDouble);  // prints 3.4
    System.out.println(myFloat);    // prints 3.4
    System.out.println(myDoubleScientific);   // prints 344.5
  }
}

Note: The floating-point literals are used to initialize float and double type variables.

4. Character Literals

Character literals are unicode character enclosed inside single quotes. For example,

char letter = 'a';

Here, a is the character literal.

We can also use escape sequences as character literals. For example, \b (backspace), \t (tab), \n (new line), etc.

5. String literals

A string literal is a sequence of characters enclosed inside double-quotes. For example,

String str1 = "Java Programming";
String str2 = "codemy";

Here, Java Programming and codemy are two string literals.