StringBuilder - Using concatenation vs using append in loop

Question

Wondering what is the best way to use it:

StringBuilder query = new StringBuilder(" Select * from mytable t where ");
for ( Object object : objects ) {
 query.append(" t.field = " + object.field ); // this one OR
 query.append( object.field ); // this one? 
}

Not sure which one is recommended to use.

• Pshemo: there is also query.append(" t.field = ").append(object.field);
• Tarik: StringBuilder seems an overkill in this particular case.

Answer 1

String builder is much faster, so it's not recommended doing concatenations of more than say 3-4 strings (outside of a loop), and definitely not in loops, I'd suggest you do like this:

for ( Object object : objects ) {
 query.append(" t.field = ");
 query.append( object.field ); 
}

Answer 2

Two separate calls to append are better. Behind the scenes, the use of + on strings results in a StringBuilder being created to do the concatenation. So, you want to either:

1. Concatenate all your strings in one shot using + (which doesn't work in your dynamic case), or

2. Use an explicit StringBuilder with a call to append for each little piece of the string you are building (don't use + anywhere).

Answer 3

Use append. However, note that if you are doing relatively few loops (say 10 - 20), then it does not really matter if you use StringBuilder and you may not see any performance improvement.