Question

Is there a performance overhead in executing sb.indexOf(c + "")
where c is of type Character or char and sb is StringBuilder object?

Answer 1

You can use String.valueOf

builder.indexOf(String.valueOf(c));

There are good things about this approch.

1. Clean code
2. String.valueOf creates String object using char[] from passed char likechar data[] = {c}; so no additional operation is required.

2 is really a micro optimization and I would always go for option 1 i.e. “clean code”.

For what it’s worth, here’s the bytecode generated by the concatenation version:

new #2; //class java/lang/StringBuilder
dup
invokespecial #6; //Method java/lang/StringBuilder."<init>":()V
aload_1
invokevirtual #7; //Method java/lang/StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
ldc #8; //String 
invokevirtual #9; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
invokevirtual #10; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
invokevirtual #11; //Method java/lang/StringBuilder.indexOf:(Ljava/lang/String;)I

As you can see, it creates a second StringBuilder, does two append calls, and then a toString. In contrast, here’s the String.valueOf version:

aload_0
aload_1
invokestatic #12; //Method java/lang/String.valueOf:(Ljava/lang/Object;)Ljava/lang/String;
invokevirtual #11; //Method java/lang/StringBuilder.indexOf:(Ljava/lang/String;)I

That just hands the Character (which has already been automatically unboxed into a char) off to String.valueOf. So what does that do? Let’s look at the JDK source code:

public static String valueOf(char c) {
    char data[] = {c};
    return new String(0, 1, data);
}

So it creates a new one-character array and hands off directly to the String constructor. Very likely to be more efficient.

But again, it’s probably a micro-optimization. The String.valueOf call makes the code clearer, which is the main thing.