Defer in Miranda

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

public class DeferExample {

    public static void main(String[] args) {
        // In Java, we use try-with-resources to automatically close resources
        try (FileWriter fileWriter = createFile("/tmp/defer.txt");
             BufferedWriter bufferedWriter = new BufferedWriter(fileWriter)) {
            
            writeFile(bufferedWriter);
        } catch (IOException e) {
            System.err.println("Error: " + e.getMessage());
            System.exit(1);
        }
    }

    private static FileWriter createFile(String path) throws IOException {
        System.out.println("creating");
        return new FileWriter(path);
    }

    private static void writeFile(BufferedWriter writer) throws IOException {
        System.out.println("writing");
        writer.write("data");
        writer.newLine();
    }
}

In Java, we don’t have a direct equivalent of the defer keyword. However, we can achieve similar functionality using the try-with-resources statement, which was introduced in Java 7.

The try-with-resources statement ensures that each resource is closed at the end of the statement. It’s a more concise and safer way to handle resources that need to be closed after we’re done with them, such as files or database connections.

In this example:

1. We create a FileWriter and a BufferedWriter in the try-with-resources statement. These will be automatically closed when the try block is exited, either normally or due to an exception.

2. The createFile method creates a new FileWriter. If there’s an error, it will throw an IOException.

3. The writeFile method writes data to the file using the BufferedWriter.

4. Any IOException that occurs during file creation or writing is caught in the catch block, where we print an error message and exit the program.

To run the program:

$ javac DeferExample.java
$ java DeferExample
creating
writing

The output confirms that the file is created and written to. The file is automatically closed when the try-with-resources block is exited, which happens implicitly at the end of the main method.

This approach provides similar benefits to the defer keyword in Go:

1. It ensures that resources are properly closed, even if an exception occurs.
2. The resource management code is kept close to where the resource is opened, improving readability.
3. It reduces the chance of resource leaks by automating the closing process.

While the syntax is different from Go’s defer, the try-with-resources statement in Java serves a similar purpose of ensuring cleanup operations are performed reliably.