ArrayList vs Vector in Java

In Java, both ArrayList and Vector are dynamic arrays that can grow or shrink in size dynamically as elements are added or removed. However, there are some key differences between the two, and it is essential to understand these differences to choose the appropriate data structure for specific scenarios. In this blog post, we will explore the dissimilarities between ArrayList and Vector in Java. 

Difference between ArrayList and Vector in Java

1. Synchronization: 

The most significant distinction between ArrayList and Vector lies in their synchronization behavior. Vector is synchronized, meaning it is thread-safe, while ArrayList is not synchronized and, therefore, not thread-safe. 

When multiple threads can access and modify the same list concurrently, using a Vector ensures that the operations are synchronized, preventing potential race conditions. On the other hand, ArrayList requires external synchronization mechanisms like Collections.synchronizedList() to make it thread-safe.

 2. Performance: 

Because of the synchronization overhead, Vector usually has slightly lower performance compared to ArrayList. In scenarios where synchronization is not required, using ArrayList is more efficient. However, with modern multi-core processors and Java's concurrent collections, the impact of synchronization has diminished, and ArrayList may still perform well in many cases. 

3. Growth Mechanism: 

Both ArrayList and Vector grow dynamically as elements are added. However, the way they expand their capacity differs. ArrayList increases its capacity by a fixed percentage (typically 50% of the current size) when it runs out of space. On the other hand, Vector doubles its capacity when it needs to grow. This doubling behavior in Vector can lead to more wasted space, especially if it has frequent insertions. 

4. Legacy Considerations: 

Vector is one of the older classes in Java, and it was part of the initial Java version (Java 1.0). As a result, it is considered part of the legacy API. On the other hand, ArrayList was introduced in Java 1.2 and is part of the Java Collections Framework, which provides a more modern and flexible set of collection classes. 

5. Usage and Recommendation: 

As of Java 9, the official Java documentation recommends using ArrayList over Vector unless there is a specific requirement for synchronization. For most use cases, ArrayList is the preferred choice due to its better performance and being part of the modern collections framework. If synchronization is necessary, other synchronized collections like Collections.synchronizedList() or CopyOnWriteArrayList (from java.util.concurrent package) should be considered instead of using Vector. 

Cheat Sheet - Difference between ArrayList and Vector in Java

Features ArrayList Vector
Thread Safety ArrayList is not thread-safe Vector is thread-safe
Performance As ArrayList is not synchronized, it provides better performance than Vector As Vector is synchronized, it performs slightly slower than ArrayList
Legacy Code ArrayList is not considered a legacy code Vector class is considered a legacy code and is due for deprecation

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