Which of the following can lead to Java memory leaks?

Circular and complex bi-directional references can indeed lead to Java memory leaks. When objects in Java reference each other in a circular manner, they create a scenario where the garbage collector is unable to reclaim memory, even if those objects are no longer needed by the application. The garbage collector relies on reference counting and reachability to identify which objects are still in use; if two objects are holding references to one another, they may prevent each other from being garbage collected, leading to an increase in memory usage over time.

In contrast, efficient thread management, optimal memory allocation, and high-performance garbage collection are practices that generally enhance application performance and memory efficiency, thus reducing the likelihood of memory leaks rather than contributing to them. These practices aim to optimize how memory and resources are utilized in Java applications, contributing to overall stability and efficiency.