Integer vs. Int: What's the difference?

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Integer vs. Int: What’s the difference?

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January 20th, 2024

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Whether you’re new to programming or have been coding for years, using Integer and int interchangeably in Java is easy. While they may seem identical at first glance, some key differences between these two data types are important to understand.

In this post, we’ll explain exactly what these are, how they’re similar, where they differ, and when you should use one vs. the other. Understanding the nuances between these primitive and wrapper types can help you write more optimized code and prevent bugs.

This topic may seem minor, but it can impact your code’s performance and memory usage. Per The App Founders ‘ research, even experienced Normal or On-Demand App Development Agency experts may sometimes use these data types incorrectly.

So don’t feel bad if you’ve been mixing them up! By the end of this app development guide, you’ll have a solid grasp on when to use Integer vs int.

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Definition of Integer and int

In Java, Integer and int represent integer values but have some key differences:

Integer is a wrapper class that wraps primitive int values into an object. It is an object (reference type) that contains an int value.

Int is a primitive data type that represents integer values. int is a value type that stores the integer value directly as 32-bit signed two’s complement integers (-2^31 to 2^31-1).

An integer is a class defined in the Java API that provides useful methods to work with the object, while int is a primitive data type built into the Java language. Since Integer is an object, it needs to be instantiated with new, whereas int variables can be declared and initialized directly.

The key distinction is that an Integer is a reference type that points to an object that holds the value, while int directly stores the 32-bit integer value.


Integer and int in Java represent whole number values with more similarities than differences. At their core, they both:

  • Represent integer values without fractions. This means they can only store whole numbers like 0, 1, 10, 255 etc.
  • Have the same value range. Integers in Java are 32-bit signed values, meaning they can store values from -2,147,483,648 to 2,147,483,647. They share this same range of possible values.
  • Support the same mathematical operations. Using both values, you can perform addition, subtraction, multiplication, division, modulo operations, and more. They behave identically for basic math.

So, they work the same way in terms of representing whole numbers and performing math. The key differences come in how they are treated by the Java language itself, which we’ll explore next. But at their core, they have more in common than not when working with integer data.

Differences between Integer and int

Both of these may seem interchangeable, but they have some important differences under the hood:

  1. Integer is an object, while int is a primitive data type. This means it is a class that wraps the int primitive in an object.
  2. The integer is nullable, but Int cannot be set to null. An Integer can take on a null value, indicating no value is assigned. An int must have a numeric value and can never be null.
  3. They have different internal representations in memory. An Integer is an object that contains an int value. The object has associated overhead in memory for storing the object’s class and other metadata. An int is just 32 bits of primitive data.
  4. They have different default values. For Integer, the default is null, while for int, it is 0. So if you declare an Integer without assigning a value, it will be null, vs an int will initialize to 0.

So, they may seem interchangeable in some situations, but under the hood, Integer is an object wrapper around the primitive int type. This leads to differences in default values, memory overhead, and nullability.

Autoboxing and Unboxing

In Java, there is automatic conversion between the primitive int type and the Integer object wrapper class. This process is known as autoboxing and unboxing.

When an int value is assigned to an Integer reference, autoboxing occurs. The int value is automatically wrapped or boxed into an Integer object. For example:

int num = 10;

Integer wrappedNum = num; // autoboxing – int is boxed into Integer

The opposite process, unboxing, happens when an Integer object is assigned to an int variable. The Integer object is unboxed, and its int value is extracted. For example:

Integer wrappedNum = new Integer (10);

int num = wrappedNum; // unboxing – int value extracted from Integer object

This automatic boxing and unboxing allows Integers to be treated similarly to primitive ints in many cases. However, there are some important differences in performance:

Autoboxing and unboxing incur a performance cost at runtime because it requires object creation and extraction. Frequent boxing and unboxing should be avoided in performance-critical sections.

Integers take more memory than ints because they are full object wrappers. Using Integers excessively can cause more pressure on the memory system and garbage collection.

So, in performance-sensitive code, it is better to use the primitive int type over the Integer wrapper class whenever possible. The autoboxing and unboxing will happen automatically as needed, but minimizing it improves efficiency.

When to use Integer vs int

In Java development frameworks, the decision between using the Integer class or the int primitive comes down to two main factors:

Use Int for simple integer values that don’t need to be null. The int primitive type is ideal for storing numbers within the range -2,147,483,648 to 2,147,483,647. It occupies 4 bytes of memory, is highly optimized by the Java compiler, and does not incur the overhead of object instantiation or garbage collection.

Use Integer when you need to store numeric values that can be null. Since int is a primitive type, it cannot be assigned null. However, the Integer wrapper class allows null values, making it ideal for representing numeric values that are unknown or missing. This comes at the cost of requiring more memory and processing power than int.

Here are some examples to illustrate when each type is preferable:

  • Use int for loop counters, array indexes, math operations, storing ages, scores, counts etc. These are simple integral values that do not need to handle nulls.
  • Use Integer when retrieving numeric values from a database that could be empty. A database field may sometimes lack a value; null is a more appropriate representation than 0.
  • Use Integer when storing numbers inside collections like ArrayLists and HashMaps. These collections require object types and won’t accept primitives like int.
  • Use Integer if you need to parse numeric Strings that might not contain a valid number. Calling Integer.parseInt(string) will throw an exception on invalid values, while Integer.valueOf(string) will return null.

So, in summary, prefer int for performance and simplicity, but use Integer when you need nullability or object-based containers. This gives you the best combination of efficiency and utility in Java.

Storing in Collections

When storing primitive values like int in a collection like ArrayList or HashMap, they are stored in their primitive form without autoboxing. This means the collections contain raw int values.

On the other hand, when storing Integer objects in a collection, autoboxing occurs. The Integer objects are stored in the collection, not the raw primitive int values.

This difference affects some behaviors:

  • Retrieving a value from the collection returns an int if the collection contains primitive int values. It returns Integer objects if the collection contains Integer objects.
  • The .contains() method checks based on the raw int value when used on a collection containing int. It checks based on the Integer object when used on a collection containing an Integer.
  • Calling methods like indexOf() and lastIndexOf() use the raw int values for comparison when the collection contains int. It uses the Integer objects when the collection contains integers.

Therefore, autoboxing only occurs when storing Integer objects in collections. Storing primitive int values avoids autoboxing. This can affect some behaviors when retrieving values and using methods that rely on checking for equality/identity.

Memory and performance

The int primitive type uses less memory than Integer objects. The int primitive type takes up 32 bits (4 bytes) of memory to store the value. However, Integer objects take up much more memory because of the overhead required to create an object in Java. The object has to store information like the class it belongs to, extra metadata used by the JVM, etc., in addition to the underlying int value.

Therefore, using the primitive int type directly can help reduce your application’s overall memory usage, especially when you need large arrays or collections of number values. This is because thousands or millions of unnecessary Integer objects occupy more cumulative heap space.

The int primitive type is also faster for computations and numerical operations. When you use Integer objects, autoboxing and unboxing must happen under the hood to convert the object wrapper to a primitive before doing calculations. This autoboxing/unboxing incurs a performance penalty. The int type avoids this extra work and can execute arithmetic and mathematical operations more efficiently.

So, in performance-critical sections of code where you need high-speed numerical computations or require optimized memory usage, the int primitive type has the advantage over using Integer objects.

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Integer and int in the Java interpretive framework seem very similar at first glance, but they have some key differences in usage and app performance metrics.

In summary, prefer int primitives when you don’t need the object and Integer when you need the object methods or immutable objects. Consider performance and memory costs when autoboxing and choosing collection types.

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