Understanding the Difference Between Integer and int in Java

What are the key differences between Integer and int in Java?

// Example of using int and Integer in Java
int primitiveInt = 5;
Integer wrapperInt = Integer.valueOf(primitiveInt); // Autoboxing
Integer anotherInt = 10; // Autoboxing
int anotherPrimitive = anotherInt; // Unboxing

In Java, `int` is a primitive data type while `Integer` is a wrapper class that encapsulates an `int` in an object. The differences affect how each can be used, especially in terms of memory allocation, null handling, and methods available.

// Autoboxing and Unboxing in Java
Integer obj = 100; // Autoboxing
int num = obj; // Unboxing

Integer parsedNumber = Integer.parseInt("123"); // Parsing a String to Integer

Causes

• `int` is a primitive data type, which means it holds a numeric value directly.
• `Integer` is an object wrapper class that can hold null and is used to represent `int` as an object.

Solutions

• Use `int` for simple numeric operations where performance is critical.
• Use `Integer` when you need to use `int` as an object, such as in collections (e.g., `ArrayList<Integer>`) or when dealing with nullable values.

Mistake: Assuming Integer can be directly assigned to int without conversion.

Solution: Always remember to unbox Integer to int when performing numerical operations.

Mistake: Using int with collections that require objects, which leads to compile-time errors.

Solution: Use Integer instead of int for storing numbers in collections like ArrayList.