When Does Java's finalize() Method Actually Get Called?

Determining the Invocation Timeframe of finalize() in Java

When working with Java objects, it's essential to understand the lifecycle of an object and its associated methods. One such method, finalize(), plays a crucial role in object cleanup. However, it's often observed that finalize() does not execute as expected. This article delves into the timing and behavior of finalize() to shed light on this issue.

Invocation of finalize()

The finalize() method is invoked when an object is scheduled for garbage collection. However, it's important to note that the exact timing of this invocation is not deterministic. The Java Virtual Machine (JVM) determines when to initiate garbage collection, and the finalize() method will be called during that process if the object is eligible for collection.

Factors Affecting Invocation

Contrary to popular belief, an object does not always undergo garbage collection and, consequently, its finalize() method may not be invoked. The object must first become eligible for garbage collection. This occurs when all references to the object are lost, making it unreachable by any part of the program.

Furthermore, garbage collection is not triggered immediately upon an object becoming eligible. The JVM considers the performance implications and may delay garbage collection to optimize resource utilization. Hence, there is no guarantee that a finalize() call will occur promptly.

Consequences of Uncertain Timing

This unpredictable timing can lead to scenarios where finalize() is not executed as expected. For instance, in simple test programs or cases where the object remains reachable, garbage collection may never occur, and finalize() will not be invoked.

Alternatives to finalize()

Given the limitations of finalize(), it's generally discouraged to rely on it for essential cleanup operations. Instead, developers should use predefined cleanup methods like close() or dispose() whenever possible. These methods ensure that resource cleanup is performed in a timely and predictable manner, regardless of whether the object is subject to garbage collection.

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