Java\'s int and Integer: Primitive vs. Object—What\'s the Difference?

Primitive vs. Object: Understanding Integer and int in Java

In Java, the difference between int and Integer stems from their fundamental nature.

int: A Primitive Data Type

int is a primitive data type that directly holds the numerical value. It occupies fixed memory space and stores the binary representation of the integer.

Integer: A Wrapper Class

Integer, on the other hand, is a wrapper class that wraps an int value. It acts like any other object in Java, with its own methods and fields. Integer variables store references to Integer objects.

Instantiation vs. Assignment

The code shown highlights this distinction:

int n = 9; // Assigns the value 9 to the primitive variable n

In this case, n directly stores the integer value 9.

// This code won't compile because Integer expects a reference to an object
Integer n = 9;

Method Invocations

Wrapper classes like Integer provide methods that allow for operations on the wrapped values. For example:

Integer.parseInt("1") // Parses a string into an int (returns an int)

Since int is not a class, it does not have methods like parseInt.

// This code won't compile
int.parseInt("1")

Autoboxing and Unboxing

Java 5 introduced autoboxing and unboxing, which automatically convert between primitive and wrapper types. This convenience can introduce subtle bugs and performance issues, so explicit conversions are recommended.

Wrapper Class Hierarchy

All primitive types in Java have equivalent wrapper classes: Byte (byte), Short (short), Integer (int), Long (long), Boolean (boolean), Character (char), Float (float), and Double (double).

Wrapper classes extend the Object class, allowing them to be used in collections and generics where object references are required.

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