With each new release, Java strives to enhance its features, performance, and maintainability. One such endeavour is Java Enhancement Proposal (JEP) 421, which aims to deprecate Object finalization and potentially remove it in Java 18. This article delves into the reasons behind this deprecation, explores potential replacements, and paves the way for a more robust approach to resource management in Java applications.
1. The Role of Object Finalization
Object finalization in Java refers to the process of cleaning up resources associated with an object before it is garbage collected. It allows us to perform crucial tasks such as closing files, releasing database connections, or deallocating native resources. Traditionally, finalization is implemented using the finalize() method, which is called by the garbage collector before reclaiming memory.
1.1 Finalization Example
public class ResourceHandler {
private File file;
public ResourceHandler(String fileName) {
this.file = new File(fileName);
}
// Finalizer method
@Override
protected void finalize() throws Throwable {
try {
// Close file resources
if (file != null && file.exists()) {
file.close();
System.out.println("File resources cleaned up.");
}
} finally {
// Call superclass finalize method
super.finalize();
}
}
}
In this example, the ResourceHandler class uses finalization to clean up file resources before garbage collection.
However, the use of finalization has long been criticized for various reasons, including its unpredictability, performance overhead, and potential for resource leaks. This has led to Java’s efforts to deprecate and potentially remove finalization altogether.
2. The Shortcomings of Finalization
While the finalize() method promised a way to release resources before garbage collection, its implementation fell short in several key areas:
- Non-deterministic Execution: The JVM offers no guarantee on when or by which thread the
finalize()method will be called. This unreliability makes it difficult to predict resource release and can lead to race conditions. - Uncertain Order: There’s no guarantee on the order in which finalizers for different objects will be executed. This becomes problematic when resource release relies on a specific sequence.
- Potential for Memory Leaks: Code within
finalize()can inadvertently resurrect the object, preventing garbage collection and causing memory leaks. - Limited Scope: Finalization only occurs when an object becomes unreachable, failing to address scenarios where resources need to be released explicitly.
- Complexity and Maintenance: Code that utilizes finalization tends to be more complex and harder to maintain, leading to potential bugs and inefficiencies.
- Performance Overhead: Finalization introduces overhead to the garbage collection process, impacting the overall performance of Java applications.
These drawbacks have made finalization a discouraged practice for a long time. Modern Java provides superior alternatives for resource management, prompting the decision for its eventual removal.
3. Java Enhancement Proposal 421
JEP 421 proposes to deprecate Object finalization for removal in Java 18. The rationale behind this proposal lies in addressing the shortcomings associated with finalization and promoting better alternatives for resource cleanup.
3.1 Key Points of JEP 421
- Deprecation of
finalize()Method: The proposal suggests marking thefinalize()method as deprecated, signalling to developers that its usage is discouraged and subject to removal in future versions of Java. - Educational Resources and Documentation: JEP 421 emphasizes the importance of educating developers about the drawbacks of finalization and guiding them towards alternative approaches for resource management.
- Potential Removal in Java 18: While not set in stone, the ultimate goal of JEP 421 is to remove finalization entirely in Java 18, providing a cleaner, more efficient approach to memory management.
4. Embracing Alternatives for Resource Management
While deprecating finalization raises concerns about resource management, Java offers several alternative approaches that are more reliable, efficient, and developer-friendly:
4.1 try-with-resources Statement
Introduced in Java 7, the try-with-resources statement provides a concise and effective way to manage external resources. By automatically closing resources at the end of the try block, it eliminates the need for explicit cleanup operations and ensures proper resource release.
Here’s an example of using try-with-resources:
import java.io.FileWriter;
import java.io.IOException;
public class TryWithResourceExample {
public static void main(String[] args) {
// Using try-with-resources to automatically close file
try (FileWriter writer = new FileWriter("javacodegeeks.txt")) {
writer.write("Hello, Java Code Geeks!");
System.out.println("Data written to file.");
} catch (IOException e) {
e.printStackTrace();
}
}
}
The above code example demonstrates the use of try-with-resources to automatically close file resources after usage, without relying on finalization.
4.3 AutoCloseable Interface
Objects that manage resources can implement the AutoCloseable interface, allowing them to be used with try-with-resources for automatic resource cleanup. This approach promotes cleaner code and reduces the likelihood of resource leaks.
public class ResourceHandler extends FileWriter implements AutoCloseable {
private final String fileName;
public ResourceHandler(String fileName) throws IOException {
super(fileName);
this.fileName = fileName;
}
public String getName() {
return fileName;
}
@Override
public void close() throws IOException {
super.close(); // Call the original FileWriter close method
System.out.println("Closed CloseableFileWriter for: " + this.getName()); // Optional logging
}
public static void main(String[] args) throws IOException {
// Using ResourceHandler with try-with-resources to automatically close file
try (ResourceHandler writer = new ResourceHandler("javacodegeeks.txt")) {
writer.write("This is some text to write to the text file.\n");
writer.flush(); // Flush the data to the underlying stream
} // writer is automatically closed here
}
}
In this example, the ResourceHandler class implements AutoCloseable and defines a close() method to perform cleanup. The main class creates a ResourceHandler object within a try-with-resources block. When the block exits (normally or due to an exception), the resource is automatically closed, even if no explicit call to close() is made. This ensures proper resource management without relying on finalization.
4.3 Cleaner API (Java 9+)
The Cleaner API provides an alternative to finalization for managing resources in Java. It offers a more explicit and controllable approach. We can register a cleaning action with an object, ensuring that the action is executed when the object becomes unreachable. This approach allows for more deterministic cleanup of resources without the unpredictability and performance overhead associated with finalization. Below is an example implementation of the Cleaner API:
ResourceHandler.java Class
public class ResourceHandler implements AutoCloseable {
private final Cleaner.Cleanable cleanable;
private final FileWriter fileWriter;
public ResourceHandler(String fileName) throws IOException {
this.fileWriter = new FileWriter(fileName);
this.cleanable = Cleaner.create().register(this, new CleanerRunnable(fileWriter));
}
// Implementing close method of AutoCloseable interface
@Override
public void close() throws IOException {
cleanable.clean();
}
// Method to write data to the resource
public void write(String data) throws IOException {
fileWriter.write(data);
fileWriter.flush(); // Flush data to ensure it's written immediately
}
// Runnable for cleaner
private static class CleanerRunnable implements Runnable {
private final FileWriter fileWriter;
public CleanerRunnable(FileWriter fileWriter) {
this.fileWriter = fileWriter;
}
@Override
public void run() {
try {
fileWriter.close();
System.out.println("Resource cleaned up by Cleaner API.");
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
CleanerExample Class (contains main method to test the ResourceHandler class implementing the Cleaner API. )
public class CleanerExample {
public static void main(String[] args) {
try (ResourceHandler handler = new ResourceHandler("javacodegeeks.txt")) {
handler.write("Hello, World!");
System.out.println("Data written to file.");
} catch (IOException e) {
e.printStackTrace();
}
}
}
Notice that we are enclosing our ResourceHandler class within a try-with-resources block.
In this implementation:
- The
ResourceHandlerclass manages aFileWriterobject to write data to a file. - The
CleanerRunnableclass implements theRunnableinterface to define the cleanup logic. - When an instance of
ResourceHandleris created, it registers itself and the associatedCleanerRunnablewith theCleanerAPI for cleanup. - The
close()method ofResourceHandlertriggers the cleanup action through theclean()method of theCleanableobject.
Output from running the test:
This implementation ensures that resources are cleaned up reliably and predictably when the close() method is called or when the ResourceHandler object is garbage collected. It eliminates the need for finalization while providing more control over resource management.
5. Benefits of Embracing Alternatives for Resource Management
These alternatives offer significant advantages over finalization:
- Deterministic Execution: The timing and order of resource release are predictable, leading to more reliable code behaviour.
- No Risk of Memory Leaks: By ensuring proper resource closure, these mechanisms eliminate the potential for memory leaks caused by accidental object resurrection.
- Explicit Control: In cases where resource release requires specific actions, these alternatives provide a more controlled environment.
6. Conclusion
The deprecation of finalization in Java 18 marks a significant step towards a more reliable and predictable resource management landscape. By encouraging developers to adopt alternative approaches such as try-with-resources , AutoCloseable interface, and the Cleaner API, Java aims to streamline resource cleanup and mitigate the risks associated with finalization.
As Java evolves, it continues to provide us with tools and practices that promote efficient software development.
7. Download the Source Code
This was an article on Deprecate Finalization in Java 18.
You can download the full source code of this example here: Deprecate Finalization in Java 18
