DAY4 JAVA DATA TYPES & VARIABLES

Java Data Types
Primitive Data Types

Primitive data types are the most basic data types available in Java. There are eight primitive data types, each serving a specific purpose:

byte:
    Size: 8-bit
    Range: -128 to 127
    Usage: Memory-efficient storage in large arrays.

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byte b = 100;
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short:

Size: 16-bit
Range: -32,768 to 32,767
Usage: Suitable for saving memory in large arrays.

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short s = 10000;
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int:

Size: 32-bit
Range: -231 to 231-1
Usage: Default choice for integer values.

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int i = 100000;
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long:

Size: 64-bit
Range: -263 to 263-1
Usage: For large integer values.

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long l = 100000L;
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float:

Size: 32-bit
Usage: For fractional numbers, with single precision.

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float f = 234.5f;
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double:

Size: 64-bit
Usage: For fractional numbers, with double precision.

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double d = 123.4;
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boolean:

Values: true or false
Usage: For simple flags and conditions.

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boolean flag = true;
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char:

Size: 16-bit
Range: 0 to 65,535 (Unicode characters)
Usage: For storing characters.

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char c = ‘A’;

Types of Variables in Java

In Java, variables are classified into three main types:

1. Local Variables

   Declared inside a method, constructor, or block.

   Scope is limited to the block where they are declared.

   Must be initialized before use.

Example:

public class LocalVariableExample {
public void display() {
int num = 10; // Local variable
System.out.println(“Local Variable: ” + num);
}
}

1. Instance Variables

   Declared inside a class but outside any method.

   Belongs to an instance of the class (each object gets its own copy).

   Initialized with default values if not explicitly assigned.

Example:

public class InstanceVariableExample {
int age = 25; // Instance variable

public void show() {
    System.out.println("Instance Variable: " + age);
}

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}

Default values for instance variables:

    int → 0

    double → 0.0

    boolean → false

    String (or any object) → null

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1. Static Variables (Class Variables)

   Declared using the static keyword inside a class but outside methods.

   Shared among all objects of the class (common memory).

   Initialized once at class loading.

Example:

public class StaticVariableExample {
static String company = “Tech Corp”; // Static variable

public void show() {
    System.out.println("Static Variable: " + company);
}

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}

Complete example:

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