When the + operator for concatenating Strings is a better option

Simple but not widely understood fact: the + operator for String concatenation is your best option, an order of magnitude better than StringBuffer.append(...), when the your String value resolves at compile time.

Take this situation

   String str = "This " + " is " + " a " + " test " + " String.";

which represents a rather simplistic example of a composite string constructed from a bunch of (predictable) strings. This will be resolved by the compiler to

   String str = "This is a test String.";

even though you used the + operator to delineate the individual strings.

Update [Jan 24, 2005]: Take a look at the bytecode for a class that declares and initializes two strings str1 (4 through 6) and str2 (7 through 39), one with each approach:

public class TestStringConcat extends java.lang.Object{

public TestStringConcat();

  Code:

   0:   aload_0

   1:   invokespecial   #1; //Method java/lang/Object."":()V

   4:   ldc     #2; //String This  is  a  test  String.

   6:   astore_1

   7:   new     #3; //class StringBuffer

   10:  dup

   11:  ldc     #4; //String This

   13:  invokespecial   #5; //Method java/lang/StringBuffer."":(Ljava/lang/String;)V

   16:  ldc     #6; //String  is

   18:  invokevirtual   #7; //Method java/lang/StringBuffer.append:(Ljava/lang/String;)Ljava/lang/StringBuffer;

   21:  ldc     #8; //String  a

   23:  invokevirtual   #7; //Method java/lang/StringBuffer.append:(Ljava/lang/String;)Ljava/lang/StringBuffer;

   26:  ldc     #9; //String  test

   28:  invokevirtual   #7; //Method java/lang/StringBuffer.append:(Ljava/lang/String;)Ljava/lang/StringBuffer;

   31:  ldc     #10; //String  String

   33:  invokevirtual   #7; //Method java/lang/StringBuffer.append:(Ljava/lang/String;)Ljava/lang/StringBuffer;

   36:  invokevirtual   #11; //Method java/lang/StringBuffer.toString:()Ljava/lang/String;

   39:  astore_2

   40:  return



}

Go ahead, write a small for-loop and test this and then compare it with the StringBuffer.append(String) method. Of course, the StringBuffer does far better in runtime String resolution situations. But you already knew that.

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