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🧬 Java Data Types – Understand What Goes Where

In Java, data types define the kind of data a variable can hold. This helps the compiler allocate memory and ensure you don’t accidentally assign text to a number or vice versa.

At GoNimbus, we believe mastering data types is the key to writing bug-free, optimized Java programs.

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📦 Two Main Categories of Data Types

Java data types are divided into:

Category	Description
Primitive	Built-in types for simple values
Non-Primitive	Objects and more complex structures

Let’s explore each.

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1️⃣ Primitive Data Types

Java has 8 built-in primitive types:

Type	Description	Size	Example Value
int	Whole numbers	4 bytes	25, -100, 0
float	Decimal numbers (single precision)	4 bytes	3.14f, -7.5f
double	Decimal numbers (double precision)	8 bytes	99.99, -0.001
char	A single character	2 bytes	'A', '9'
boolean	True or false	1 bit	true, false
byte	Small integers (-128 to 127)	1 byte	100, -50
short	Medium-range integers	2 bytes	5000, -1500
long	Large whole numbers	8 bytes	150000L, -99999L

✅ Quick facts:

• Use float for memory-efficient decimals (add f suffix)
• Use long for big numbers (add L suffix)
• Use boolean for condition flags and checks

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👨‍💻 Example – Using Primitives

public class PrimitiveDemo {
  public static void main(String[] args) {
    int age = 25;
    float score = 95.5f;
    char grade = 'A';
    boolean passed = true;

    System.out.println("Age: " + age);
    System.out.println("Score: " + score);
    System.out.println("Grade: " + grade);
    System.out.println("Passed: " + passed);
  }
}

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2️⃣ Non-Primitive Data Types

Also called reference types, these include:

Type	Description
String	A sequence of characters (text)
Arrays	A collection of values (fixed-size)
Classes	Custom objects and blueprints
Interfaces	Contracts that classes can implement

Let’s start with the most common one: String.

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📘 String: Most Used Non-Primitive Type

String city = "Hyderabad";
System.out.println("City: " + city);

✅ Strings support powerful built-in methods:

System.out.println(city.length());       // Output: 9
System.out.println(city.toUpperCase());  // Output: HYDERABAD

📌 While String may feel like a primitive, it’s actually an object (with methods!).

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🧠 GoNimbus Tips for Choosing the Right Type

• Use int for counting items or IDs
• Use float/double for prices, weights, scores
• Use char for gender, grades, initials
• Use boolean for true/false conditions
• Use String for names, messages, text inputs

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⚠️ Be Careful With Type Mismatch

int age = "twenty";   // ❌ Error – type mismatch
boolean active = "true"; // ❌ Error – needs true/false without quotes

Use appropriate types without quotes unless it’s a String.

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