As it says in the doc, we need to carefully check which places are single-threaded before replacing everything by StringBuilder.
Can you give me an example of when using StringBuffer in a multi-threaded context makes sense. 
These methods call only be called by one thread at a time safely, so using StringBuffer doesn't buy anything.
ObjectNameFactory.addProperty(String name, String value)
SessionSessing.getToken(Reader)
In all other cases StringBuffer is used as a local variable, i.e. thread local variable.
The ObjectNameFactory.addProperty() method makes for an interesting puzzle.
Write a program which will generate all the possible outcomes of
[code]
// thread 1
objectNameFactory.addProperty("a", "b");
// thread 2
objectNameFactory.addProperty("c", "d");
[code]
You have the obvious
[code]
a=b,c=d
c=d,a=b
[code]
but also
[code]
ac==bd
a,c=b=d
[code]
and many more
I have generated the list
a=b,c=d
a=,bc=d
a=,cb=d
a=,c=bd
a,=bc=d
a,=cb=d
a,=c=bd
a,c=b=d
a,c==bd
c=d,a=b
c=,da=b
c=,ad=b
c=,a=db
c,=da=b
c,=ad=b
c,=a=db
c,a=d=b
c,a==db
a=bc=d
a=cb=d
a=c=bd
ac=b=d
ac==bd
c=da=b
c=ad=b
c=a=db
ca=d=b
ca==db
Good point. To be honest I did not check the code on usages of StringBuffer yet. I was only aware of the usage referred to in QFJ-736.