Implements Closeable or implements AutoCloseable

java

resource-management

best-practices

java-7

byAlex Kataev·Jan 7, 2025

Choose Closeable when dealing with strict I/O resources that require IOException handling. Opt for AutoCloseable for a more extensive use, including non-I/O resources as it can handle any exceptions, including RuntimeExceptions. In modern Java applications, AutoCloseable is typically the better choice.

Example:

class MyResource implements AutoCloseable {
  @Override
  public void close() {   
    // Always cleans up, never leaves a mess
  }
}

// Life's too short for manual resource management
try (MyResource resource = new MyResource()) {
  // resource at your service
}

Determining the Right Interface for Closing Resources

Both Closeable and AutoCloseable interface allows resources to land back safely after their flight. Your choice between these two depends primarily on the type of the resource and the exceptions you're preparing to handle.

Respecting Elder (Closeable): If you're dealing with pure I/O operations, the old school Closeable has your back. It demands that close() throws an IOException - a checked exception specific for I/O operations, respecting the golden rules of not breaking older Java I/O operations.

Enjoying Flexibility (AutoCloseable): For anything beyond I/O operations, pick AutoCloseable. It's the chill, flexible friend that lets the close() method throw any exception, be it a checked or a runtime exception.

Best Practices for Implementing These Interfaces

The Echo Rule

With both interfaces, make your close() method idempotent. This means it should behave like an echo in an empty room - no matter how many times you shout, you only hear your echo once. In short, calling close() multiple times shouldn't cause any additional effect.

The Always-Clean Rule

Make sure your close() method can clean its room even after a wild party (throwing exceptions). Traditionally, this room-cleaning happens in a finally block. try-with-resources won't save you from ensuring this.

The Paranoid Rule

Be paranoid and confirm that your resources are truly closed. Consider additional checks in your close() method to prevent any resource leaks - the silent killers of performance.

Evolution of Resource Management in Java

Looking at the evolution of Java, you'll notice that AutoCloseable was a game-changer in Java 7. It adapted resource management to become more straightforward and universal. On the other hand, Closeable has been the reliable old acquaintance that still serves in places where older Java applications exist.