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Proper Use Of String And StringBuffer In Java
// This isn't really code at all, this is a comment that I use
// over and over again as I go through code written by people
// who obviously don't understand when to use a String and when
// to use a StringBuffer.
// I put this block of text wherever I find problems with Strings
// and StringBuffers to improve understanding of how each one works
// and when to use one or the other.
//
// Rule #1: Use a StringBuffer if you intend to build a string out of
// dynamic elements. That is, if you are going to include the results
// of function calls or variables as part of the string then you use
// a StringBuffer and do append() calls. StringBuffer's append is
// much faster than using "+" to stick together String objects.
//
// Rule #2: But, if you are just building a string out of static pieces
// of text, it's better to use Strings and "+" than creating a
// StringBuffer and making append calls. Instead just use a String
// and a bunch of "+" signs between the sections. For example:
// String test = "this " + "is " + "a " + "test " + "string";
// is _not_ expensive. Why? Because all the pieces are static text and
// the compiler can make it into this _as it compiles the code_:
// String test = "this is a test string";
//
// Rule #3: For goodness sake, do this:
// StringBuffer test = new StringBuffer();
// test.append("static string ");
// test.append(dynamicCall());
// test.append(" another static string ");
// test.append(someVariable);
// DON'T DO THIS:
// StringBuffer test = new StringBuffer();
// test.append("static string " + dynamicCall());
// test.append(" another static string " + someVariable);
// This is officially the worst of all worlds. You need to use a
// StringBuffer in this case because you've got some dynamic parts
// but there is still addition going on between dynamic parts (the
// function call and variable) and static strings. Ack!
//
// If you can't remember anything else, remember this:
// static strings = String and "+"
// dynamic strings = StringBuffer and append() 
Comments
Alan Emke replied on Tue, 2009/06/09 - 11:36am
Snippets Manager replied on Tue, 2009/03/03 - 12:05pm
Snippets Manager replied on Mon, 2008/12/15 - 10:09am
StringBuilder test = new StringBuilder( "static string " ).append( dynamicCall() ).append( "another static string ").append( someVariable );Saves real estate :D Also, unless you are planning on needing synchronized "appending", StringBuilder is faster.Snippets Manager replied on Tue, 2008/07/29 - 4:46pm
StringBuffer test = new StringBuffer(); test.append("static string "); test.append(dynamicCall()); test.append(" another static string "); test.append(someVariable);you can do:StringBuffer test = new StringBuffer(); test.append("static string ").append(dynamicCall()).append(" another static string ").append(someVariable);