How can a Java application have a memory leak despite garbage collection?

Defines managed memory leaks as unwanted reachability and connects caches, listeners, class loaders, ThreadLocal values, and queues to retaining paths.

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TL;DR

A Java memory leak usually means the application unintentionally keeps objects reachable after their useful lifetime. Common causes include unbounded caches, static collections, registered listeners that are never removed, queued work that never drains, and ThreadLocal values that outlive the request. The garbage collector is behaving correctly because a path from a GC root still reaches the objects. Fixing the leak means fixing that retaining reference or its ownership policy.

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Ownership and retention reasoning plus the ability to trace a growing object graph to a GC root.

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Core answer
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Overview
The collector can reclaim unreachable objects, but it cannot decide that a reachable object is no longer useful.
A Java memory leak usually means the application unintentionally keeps objects reachable after their useful lifetime. Common causes include unbounded caches, static collections, registered listeners that are never removed, queued work that never drains, and ThreadLocal values that outlive the request. The garbage collector is behaving correctly because a path from a GC root still reaches the objects. Fixing the leak means fixing that retaining reference or its ownership policy.
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I look for growth across comparable heap snapshots, then examine dominator size and the path from suspicious objects to a GC root. A cache may need a maximum size, expiry, weak keys, or explicit invalidation depending on its contract. A listener needs symmetrical registration and removal, while an executor queue needs capacity and backpressure. Increasing heap can delay the failure but does not correct monotonic unwanted retention.

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Calling every high-memory process a leak.
Increasing heap without inspecting retention.
Looking only at shallow object size.

How can a Java application have a memory leak despite garbage collection?

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