How to optimize the use of arrays and collections in Java to improve performance?

Optimize Java array and collection performance: For different types of elements, use basic type arrays (same type) or object arrays (different types). According to the application requirements, choose the appropriate collection class: List stores ordered elements, Set stores non-repeating elements, and Map stores key-value pairs. Optimize collection traversal: Using Iterator is more efficient than for-each loop and avoids the creation of intermediate collections. Use best practices: pre-allocate collections, use streaming APIs, avoid immutable collections, leverage parallel streams.

Optimizing the use of arrays and collections in Java to improve performance

Preface

In Java, optimizing the use of arrays and collections is critical to improving application performance. By choosing the right data structures, leveraging the Java Collections Framework, and adopting best practices, you can significantly improve the efficiency of your code.

Use an appropriate array

• Basic type array: For scenarios where a large number of elements of the same type need to be stored (such as int[]) , please use basic type array. It is faster and takes up less space than an array of objects.
• Object array: If you need to store elements of different types, use Object[]. However, it is slower than an array of primitive types and takes up more space.

Choose the appropriate collection

The Java Collections Framework provides a variety of collection classes, each with its own unique characteristics:

• List: Used to store a collection of ordered elements, such as ArrayList.
• Set: A collection used to store non-repeating elements, such as HashSet.
• Map: Used to store a collection of key-value pairs, such as HashMap.

Depending on the specific needs of your application, choosing the most appropriate collection can significantly improve performance.

Practical case: Optimizing collection traversal

The following example shows how to improve performance by optimizing collection traversal:

List<Integer> list = new ArrayList<>();
// 使用普通 for-each 循环遍历
for (int num : list) {
    // 处理元素
}

This can be optimized as:

List<Integer> list = new ArrayList<>();
// 使用 Iterator 遍历
Iterator<Integer> iterator = list.iterator();
while (iterator.hasNext()) {
    // 处理元素
}

Iterator traversal is faster than for-each loop because it does not create intermediate collections.

Best Practices

• Use pre-allocated collections to avoid frequent reallocation operations.
• Use the streaming API introduced in Java 8 and higher for efficient data processing.
• Avoid using immutable collections (such as Collections.unmodifiableList()) as it causes additional overhead.
• When possible, use parallel streams to take full advantage of multi-core processors.

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