What data types exist in Java?

In Java, there are primitive and reference data types.

Primitive Data Types: They directly store values. Their size and value range are defined by the Java specification.

• Integer types:
  • byte: 8 bits, from -128 to 127.
  • short: 16 bits, from -32768 to 32767.
  • int: 32 bits, from -2^31 to 2^31-1. The most commonly used integer type.
  • long: 64 bits, from -2^63 to 2^63-1. For very large integers.
• Floating-point types:
  • float: 32 bits, single precision according to IEEE 754 standard.
  • double: 64 bits, double precision according to IEEE 754 standard. The most frequently used type for fractional numbers.
• Character type:
  • char: 16-bit Unicode character.
• Boolean type:
  • boolean: stores true or false.

Reference Data Types: They do not store data directly but store a reference (memory address) to an object containing data. They include classes, interfaces, arrays, and enumerations (enums).

• Classes:
  • For example, String, Integer, ArrayList, and any user-defined class.
• Interfaces:
  • For example, List, Map.
• Arrays:
  • For example, int[], String[].
• Enums:
  • They are a special type of class.

Example of declaring and using primitive and reference types:

class DataTypeExample {
    public static void main(String[] args) {
        // Primitive types
        int age = 30; // Integer
        double balance = 1500.75; // Floating-point
        char initial = 'J'; // Character
        boolean isActive = true; // Boolean

        // Reference types
        String name = "John Doe"; // String class
        int[] numbers = {1, 2, 3}; // Array of integers
        java.util.ArrayList<String> cities = new java.util.ArrayList<>(); // ArrayList class
        cities.add("New York");

        System.out.println("Age: " + age);
        System.out.println("Balance: " + balance);
        System.out.println("Initial: " + initial);
        System.out.println("Is Active: " + isActive);
        System.out.println("Name: " + name);
        System.out.println("First number in array: " + numbers[0]);
        System.out.println("First city: " + cities.get(0));
    }
}

The key difference: primitive types store values directly, while reference types store references to objects. Primitive types have a fixed size, reference types do not (size depends on the object's content). When assigning primitive types, the value is copied; when assigning reference types, the reference is copied.