Re: Letter 'L'/'l' suffixed to a number for 'long' type

Eric Sosman <esosman@ieee-dot-org.invalid>
Mon, 30 Jul 2007 08:46:17 -0400
Roedy Green wrote:

I found in some code the following 'sleep(1000L)': I'd just
like to know what padding an 'L' after 1000 does. What
would be the difference with a simple 'sleep(1000)' ?

L means it is a long literal. 1000 is an int. It will automatically
be promoted to long.

     Clarification: Roedy does not mean that all int values
are automatically promoted to long, and indeed they are not.
But when the Java compiler sees `sleep(1000)' it first tries
to find a method named sleep that takes an int argument. If
no such method exists Java will look for alternatives. In
this case (assuming sleep is Thread.sleep), it finds that
there *is* a method named sleep that takes a long argument.
Since Java knows how to promote an int to a long, it makes
the conversion and calls the long-accepting sleep method.

     By using `sleep(1000L)' in the first place, the writer
saved the compiler from all this rummaging around (not very
important) and also made it plain to people reading the code
that the call was to a method taking a long argument -- that
is, the writer saves *you* from the same rummaging around
that the compiler goes through.

     To experiment with how this works, ponder the following
class and predict its output, then compile it and check
your predictions:

    class Promote {
        void m(double d) { System.out.println("double: " + d); }
        void m(long l) { System.out.println("long: " + l); }
        // void m(int i) { System.out.println("int: " + i); }
        void m(short s) { System.out.println("short: " + s); }
        void m(Object o) { System.out.println("object: " + o);

        public static void main(String[] unused) {
            m( (byte)1 );
            m( (short)2 );
            m( 3 );
            m( 4L );
            m( 5.0f );
            m( 6.0 );
            m( new Integer(7) );
            m( "eight" );

For extra credit, predict what would happen if you removed
the // from the fourth line (and check your prediction).

Eric Sosman

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