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September 8, 2023

Non Generic Vs Generic Collection

Unlock coding efficiency with our guide to generic vs. non-generic collections in Java. Make informed choices for better software development!

Non Generic Vs Generic Collection

In the dynamic realm of software development, collections emerge as quiet pillars, seamlessly managing the data that fuels our applications. Imagine an expansive library, with books thoughtfully arranged by size, genre, and language. Each tome is strategically positioned, enabling the librarian to quickly identify and deliver the precise information a visitor requires. In the digital sphere of programming, collections play the role of these librarians, orchestrating data to ensure developers can access, modify, and display it with finesse.

When we talk about collections, every developer has to make a very important choice, which is whether to use non-generic or generic collections. Imagine if the bookshelves in our library were split into two different parts: one for books in known genres and one for books in any genre. This choice affects how well the library works, how easy it is to find books, and how the users feel overall. In the same way, in programming, the choice between these collection types has a big effect on how fast, stable, and easy to maintain a software project will be in the future.: whether

Understanding the Basics

Before delving into the specifics, it's crucial to understand the fundamental concepts behind these two types of collections.

Generic Collections

Generic collections are added to programming to improve type safety and make code easier to use more than once. They let programmers make collections that are strongly typed, which means they can only store a certain kind of data. This makes sure that the data is always correct and that the type is correct throughout the program.

Non-Generic Collections

On the other hand, non-generic collections don't have to hold a certain type of data. They give organizations more freedom because they can store different kinds of elements in the same collection. However, this flexibility comes at the expense of type safety since developers have to deal with type casting and the possibility of data inconsistencies.

Data Mismatch

In the scenario of constructing an ArrayList intended for the storage of students' names, an inadvertent inclusion of an integer object rather than a string might occur. The compiler, however, permits this mismatch. Yet, complications arise during the data retrieval phase from the ArrayList, generating issues at runtime, particularly for a Non-generic ArrayList.


In the above Java program, we've created a simple demonstration of how not using generics can lead to runtime exceptions. The program uses an ArrayList without specifying a data type, essentially making it a non-generic collection. We then proceed to add elements of different types - a string, an integer, and a boolean - to the collection.

The problem arises when we try to access these elements. Since we didn't specify the data type when creating the collection, Java treats all elements as Object types. This means that when we retrieve an element from the collection, we need to explicitly cast it to the correct data type. However, this approach is error-prone and can lead to runtime exceptions.

In the provided code, we attempt to cast an integer element to a string and a boolean element to an integer. These actions are logically incorrect and result in a ClassCastException at runtime, causing the program to terminate abruptly.

Now, let's modify the code to use generics and observe how they prevent these runtime issues:

In this modified code, we've used generics by specifying the data type of the elements that the ArrayList will hold. By declaring ArrayList<String>, we indicate that this collection will exclusively contain strings. As a result, when we add a string to the collection, we don't need to perform any typecasting when retrieving the element. This ensures type safety and eliminates the risk of runtime exceptions caused by incorrect casting.

Type Safety

In this example, we'll use a non-generic collection (ArrayList) to demonstrate how type casting is needed whenever working with non-generic collections, and how this can lead to runtime errors. We'll then compare this with a generic collection to show how generics eliminate the need for such typecasting.

Non-Generic Collection Example:


In the above example, we create a non-generic ArrayList without specifying any data type. We then add elements of different data types - a string, an integer, and a boolean - to the collection. When we retrieve these elements, we need to explicitly cast them to their respective data types.

However, notice that when we try to cast a boolean value to an integer, a ClassCastException occurs at runtime. This is because we're trying to perform an invalid type cast, which results in an error and program termination.

Generic Collection Example:


In the generic example, we create a generic ArrayList with the data type explicitly set to Integer. This means that the collection can only hold integer values. We add an integer element to the collection without the need for typecasting.

When we retrieve the integer value, notice that there's no type casting required. This is because the generic type information is known at compile-time, ensuring type safety and eliminating the need for explicit type casting.

The Power of Specialization: Non-Generic Collections

Non-generic collections, also known as "untyped" collections, have their unique advantages in certain scenarios. Let's explore some of the key scenarios where non-generic collections shine:

1. Legacy Codebases and Interoperability

In situations where someone is dealing with legacy codebases or integrating with external systems, non-generic collections can prove invaluable. Older systems might not be designed to work with generic types, and using generic collections could lead to compatibility issues. Non-generic collections allow for seamless data exchange between systems with different data structures and types. For instance, in a survey conducted by VMware and MIT Technology Review, it was found that professionals encountered challenges when integrating new software with legacy systems, highlighting the relevance of non-generic collections in such contexts.

2. Mixed-Type Data

Consider a scenario where organizations need to collect data of different types but still want to keep them together for processing. Non-generic collections offer a straightforward solution. For example, when dealing with user input that includes strings, integers, and booleans, a non-generic collection can store these diverse data types without the need for excessive type conversion.

3. Dynamic Data Structures

Dynamic scenarios, where the structure of the data evolves during runtime, can benefit from non-generic collections. For instance, a dynamic form that allows users to add fields as needed would be more easily managed using a non-generic collection, as the types of data to be stored are not known in advance.

The Elegance of Type Safety: Generic Collections

While non-generic collections possess their own charm, generic collections shine in scenarios where type safety and code clarity are paramount. Let's explore some of the compelling reasons to opt for generic collections:

1. Type Safety

Programming often involves errors linked to types, causing issues in the software. According to a case study conducted by Google, approximately 20% of software defects in Java are attributed to type mismatches. Generic collections come to the rescue by making sure only the right data type is used, preventing unexpected errors due to type mix-ups.

2. Performance

a) Enhancement

In terms of performance, generic collections hold an advantage due to their ability to specify data types upfront. This allows the compiler to optimize the code, resulting in faster execution. Non-generic collections, lacking this optimization, require runtime checks and conversions, which can slow down performance and potentially introduce errors.

b) Degradation

The University of Oregon conducted a study where they analyzed 100,000 lambda expressions in open-source Java projects. The findings indicated that around 20% of the generic Functional Interfaces could be exchanged with their more specific alternatives. Utilizing generic Functional Interfaces leads to Autoboxing and Unboxing between primitive and object types, such as int and Integer. This process significantly diminishes performance.

3. Code Readability and Maintainability

Using generic collections makes handling large amounts of code much easier. The code becomes simpler to understand because type declarations make intentions clear. Developers have also emphasized that readable code is crucial for maintaining and improving software quality.

Finding the Balance: When to Choose What

The decision between non-generic and generic collections ultimately boils down to the specific requirements and characteristics of a project. To aid in making an informed choice, consider the following guidelines:

1. Project Scope and Goals

Understand the scope and goals of the project. If a project demands maximum type safety and performance optimization, generic collections should be preferred. Conversely, if the project involves dynamic or mixed-type data, non-generic collections may be more suitable.

2. Codebase and Team Competency

Evaluate the team's familiarity with both types of collections and the existing codebase. If a team is well-versed in handling generic collections and the codebase can be seamlessly adapted, it's wise to leverage their advantages. However, if someone is dealing with legacy systems or a team less experienced with generics, non-generic collections might be the pragmatic choice.

3. Performance vs. Flexibility Tradeoff

Consider the tradeoff between performance and flexibility. If an application's performance is a critical factor and one can accurately predict the data types, then generics might provide the ideal solution. On the other hand, if someone requires a more flexible approach to handling varied data, non-generic collections might suit their needs better.


In the ever-evolving landscape of software development, the choice between non-generic and generic collections holds a pivotal role in shaping the efficiency, reliability, and maintainability of codebases.

As we reflect on the insights gained, it's evident that the move from non-generic to generic collections embodies the industry's dedication to crafting code that is both robust and readable. While non-generic collections offer flexibility, they are accompanied by type safety concerns and potential runtime errors. On the other hand, generic collections provide a shield of type safety, compile-time checks, and streamlined code readability, enhancing the reliability and maintainability of software systems.

For more in-depth insights into the dynamic world of programming and software development, explore such articles on our website. At Cogent University, we understand the critical role that such knowledge plays in the evolution of a developer's skills. Our comprehensive programs empower individuals to stay ahead in the ever-evolving world of technology.

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