Is using int + "" bad for converting Java int's to Strings?

Question

So our computer science teacher taught us how to convert ints to Strings by doing this:

int i=0;
String s = i+"";

I guess he taught it to us this way since this was relatively basic computer science (high school class, mind you), but I was wondering if this was in some way "bad" when compared to:

int i=0;
String s = Integer.toString(i);

Is it more costly? Poor habit? Thanks in advance.

Answer 1

In theory

The instruction

String s = i + "";

does the following: convert i to String by calling Integer.toString(i), and concatenates this string to the empty string. This causes the creation of three String objects, and one concatenation.

The instruction

String s = Integer.toString(i);

does the conversion, and only the conversion.

In practice

Most JIT compilers are able to optimise the first statement to the second one. I wouldn't be surprised if this optimisation is done even before (by the javac compiler, at compilation of your Java source to bytecode)

Answer 2

i+""

is equivalent to

new StringBuilder().append(i).append("").toString();

so yes it is less efficient, but unless you are doing that in a loop or such you probably won't notice it.

[edited: from comments by StriplingWarrior-thanks]