How to Avoid Instantiating New Objects Inside Loops in PMD?

What are the reasons for avoiding the instantiation of new objects inside loops when using PMD?

for (int i = 0; i < n; i++) {
    List<MyObject> myObjects = new ArrayList<>(); // Avoid this
    myObjects.add(new MyObject());
}

Instantiating new objects inside loops can lead to performance inefficiencies and increased memory usage. PMD (Programming Mistake Detector) discourages this practice as it can generate a considerable number of temporary objects, which may lead to frequent garbage collection and slow down application performance.

List<MyObject> myObjects = new ArrayList<>();
for (int i = 0; i < n; i++) {
    myObjects.add(new MyObject()); // This is acceptable but consider reusing objects! 
}

Causes

• Increased memory utilization due to the creation of multiple object instances in each iteration.
• Frequent garbage collection which may affect the application’s performance adversely during runtime.
• Difficulties in code readability and maintainability when temporary objects are scattered throughout loops.

Solutions

• Refactor the code to instantiate objects outside of loops when possible.
• Reuse existing objects by clearing their state instead of creating new instances each time.
• Implement the object pool design pattern to manage object creation more efficiently.

Mistake: Instantiating new objects without considering the loop iteration count.

Solution: Always calculate whether instantiating an object is necessary within the loop.

Mistake: Failing to identify opportunities to reuse objects.

Solution: Evaluate application logic for opportunities to clear and reuse objects.