Java Variables and Data Types, Variable Scope and Lifetime

Variables

Act as containers to store data that can be referenced and manipulated in a program. Each has a specific type, determining the kind of data it can hold.

Declaring a variable

int age;
double salary;
String name;
char middleName;

It specify the data type, followed by the variable name.

Variable Initialization

int age = 19;
double salary = 20000.9876;
String name = "Grrrr";
char middleName = 'G';

Variables are declared or later in the code

Statically-typed Language

Java is a _____________, meaning each variable must have a type defined at compile time.

Primitive Data Types
Reference Data Types

Two primary data types of Java.

byte
short
int
long
float
double
char
boolean

Primitive Data Types

byte

1 byte which are used for small numbers that ranges from -128 to 127.

short

2 bytes which is suitable for slightly larger numbers that ranges from -32,768 to 32,767.

int

4 bytes which commonly used integer type that ranges from -2³¹ to 2^31-1.

long

long bigNumber = 12345678L;

8 bytes which uses for a larger integer type that uses L suffix for literals.

float

float pi=3.14F;

4 bytes which is a single-precision floating point that uses F suffix.

double

8 bytes which is a double-precision floating point and default for decimal values.

char

2 bytes which stores a single Unicode character.

boolean

1 byte which holds true or false.

Reference Data Types

These include classes, interfaces, and arrays, such as String, arrays (int[]), and custom classes. Unlike primitives, they store references to objects rather than the object itself.

Scope

The section of the code where a variable can be accessed.

Local Variables

Declared within a method and accessible only within that method.

Instance Variables (Fields)

Declared within a class but outside any method. They belong to the instance of the class.

Class Variables (Static Fields)

Declared with the static keyword and shared across all instances of the class.

Lifetime

The period during which a variable occupies memory. Local variables are deleted after method execution, while instance and class variables persist as long as the object or class exists

Deleted

Lifetime is when a variable occupies memory. Local variables are ______ after method execution, while instance and class variables persist as long as the object or class exists

Persist

Lifetime is when a variable occupies memory. Local variables are deleted after method execution, while instance and class variables _______ as long as the object or class exists.