Dead-code elimination: Java Logging

In my previous article, we have seen how the Java compiler (javac), inlines final declared variables as a compile-time optimisation.

Today, we are going to focus in dead-code elimination. Dead-code elimination is the process, where the compiler removes part of code that will never be executed.

Java logging: a simple use case

Let's say that we need to build a simple logging facility for our Java program and the requirements indicate to have the classic interface of methods; info and debug.

The tricky part with the logging, is that usually it is some kind of string, serialized. The anti-pattern that happens all the time, is that the string message is usually evaluated, even if the logging level ignores it in the end.

So, this is the Logging class:

public class Logger {
    private final static Logger defaultInstance;
    private final static boolean debugMode = true;

    static {
        defaultInstance = new Logger();
    }

    private Logger() {
        // empty
    }

    public void info(String fmt, Object ... args) {
        System.out.printf(fmt, args);
    }

    public void debug(String fmt, Object ... args) {
        if (debugMode) {
            System.out.printf(fmt, args);
        }
    }
 
    public static Logger…