Java Preprocessor

Question

If I have a boolean field like:

private static final boolean DEBUG = false;

and within my code I have statements like:

if(DEBUG) System.err.println("err1");

does the Java preprocessor just get rid of the if statement and the unreachable code?

Answer 1

Most compilers will eliminate the statement. For example:

public class Test {

    private static final boolean DEBUG = false;

    public static void main(String... args) {
        if (DEBUG) {
            System.out.println("Here I am");
        }
    }

}

After compiling this class, I then print a listing of the produced instructions via the javap command:

javap -c Test
    Compiled from "Test.java"
    public class Test extends java.lang.Object{
    public Test();
      Code:
       0:   aload_0
       1:   invokespecial   #1; //Method java/lang/Object."":()V
       4:   return

    public static void main(java.lang.String[]);
      Code:
       0:   return

    }

As you can see, no System.out.println! :)