What is more efficient StringBuffer new() or delete(0, sb.length())?

Question

It is often argued that avoiding creating objects (especially in loops) is considered good practice.

Then, what is most efficient regarding StringBuffer?

StringBuffer sb = new StringBuffer();
ObjectInputStream ois = ...;

for (int i=0;i<1000;i++) {

    for (j=0;i<10;j++) {
        sb.append(ois.readUTF());
    }
    ...

    // Which option is the most efficient? 
    sb = new StringBuffer(); // new StringBuffer instance?
    sb.delete(0,sb.length()); // or deleting content?

}

I mean, one could argue that creating an object is faster then looping through an array.

Answer 1

First StringBuffer is thread-safe which will have bad performance compared to StringBuilder. StringBuilder is not thread safe but as a result is faster. Finally, I prefer just setting the length to 0 using setLength.

sb.setLength(0)

This is similar to .delete(...) except you don't really care about the length. Also probably a little faster since it doesn't need to 'delete' anything. Creating a new StringBuilder (or StringBuffer) would be less efficient. Any time you see new Java is creating a new object and placing that on the heap.

Note: After looking at the implementation of .delete and .setLength, .delete sets length = 0, and .setLength sets every thing to '\0' So you may get a little win with .delete