Storing in variable vs. having multiple different methods

Question

What are the pros and cons of using this:

String a = new String();
switch (i) {
case 1: a = "Cueck"; break;
case 2: a = "Blub"; break;
case 3: a = "Writing cases is BORING!"; break;
}
System.out.println(a);

Versus:

switch (i) {
case 1: System.out.println("Cueck"); break;
case 2: System.out.println("Blub"); break;
case 3: System.out.println("Writing cases is BORING!"); break;
}

Which generates better bytecode? And which generates more bytecode?

Answer 1

Your first option is neater and has less redundant code. One suggested change:

String a;

switch (i) {
  case 1: a = "Cueck"; break;
  case 2: a = "Blub"; break;
  case 3: a = "Writing cases is BORING!"; break;
  default: throw new IllegalStateException("Unknown option!");
}

System.out.println(a);

Don't create a String unnecessarily - a should be instatiated when required. A default case should either throw an exception or set a to a default value.

Which generates better bytecode? And which generates more bytecode?

I wouldn't worry about that. This doesn't strike me as a likely bottleneck in any real-life application. Also, you cannot be sure what the JVM will do to optimise the byte-code once your application is running.

Answer 2

Using javap -c classname you can check the bytecode yourself,

Here's option 1:

(Note, I had to initialise a = null otherwise it doesn't compile)

   7:   aconst_null
   8:   astore_2
   9:   iload_1
   10:  tableswitch{ //1 to 3
                1: 36;
                2: 42;
                3: 48;
                default: 51 }
   36:  ldc     #3; //String Cueck
   38:  astore_2
   39:  goto    51
   42:  ldc     #4; //String Blub
   44:  astore_2
   45:  goto    51
   48:  ldc     #5; //String Writing cases is BORING!
   50:  astore_2
   51:  getstatic       #6; //Field java/lang/System.out:Ljava/io/PrintStream;
   54:  aload_2
   55:  invokevirtual   #7; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   58:  return

Here's option 2:

   7:   iload_1
   8:   tableswitch{ //1 to 3
                1: 36;
                2: 47;
                3: 58;
                default: 66 }
   36:  getstatic       #3; //Field java/lang/System.out:Ljava/io/PrintStream;
   39:  ldc     #4; //String Cueck
   41:  invokevirtual   #5; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   44:  goto    66
   47:  getstatic       #3; //Field java/lang/System.out:Ljava/io/PrintStream;
   50:  ldc     #6; //String Blub
   52:  invokevirtual   #5; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   55:  goto    66
   58:  getstatic       #3; //Field java/lang/System.out:Ljava/io/PrintStream;
   61:  ldc     #7; //String Writing cases is BORING!
   63:  invokevirtual   #5; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   66:  return

Personally, I don't think there's better bytecode in this instance, I find option 1 more readable.