Java - Variables & Objects

Variable in Java:

A variable is a named storage location used to hold a value of a particular data type.

For example:

int age = 20;
String name = "Gowtham";

Here:

• int is the data type.
• age is the variable name.
• 20 is the value stored in the variable.
• String is the type used to represent text.
• name is the variable name.
• "Gowtham" is the text value.

Types of Variables in Java

Java has three main categories of variables based on where they are declared.

1. Local Variable

A local variable is declared inside a method, constructor, or block.

void display() {
int age = 20;
System.out.println(age);
}

2. Instance Variable

An instance variable is declared inside a class but outside methods. Each object has its own instance fields.

class Student {
String name = "Gowtham";
int age = 20;
}

3. Static Variable

A static variable belongs to the class rather than to individual objects.

class Student {
static String college = "ABC College";
}

The static variable college is shared at the class level.

Object in Java?

An object is an instance of a class.

A class defines the data and behaviors that its objects can have.

For example, Student can be a class, while individual students can be represented by objects of that class.

Example

`class Student {
String name;
int age;

void display() {
    System.out.println(name);
    System.out.println(age);
}

}

public class Main {
public static void main(String[] args) {
Student s1 = new Student();

    s1.name = "Gowtham";
    s1.age = 20;

    s1.display();
}

}`

Output:

Gowtham
20

Explanation

• Student is the class.
• s1 is a reference variable.
• new Student() creates a new Student object.
• s1.name assigns a name to the object.
• s1.age assigns an age to the object.
• s1.display() calls the object's method.