String valueOf vs concatenation with empty string

java

public void foo(){
int intVar = 5;
String strVar = intVar+"";    
}

This approach uses StringBuilder to create resultant String

public void foo();
  Code:
   0:   iconst_5
   1:   istore_1
   2:   new     #2; //class java/lang/StringBuilder
   5:   dup
   6:   invokespecial   #3; //Method java/lang/StringBuilder."<init>":()V
   9:   iload_1
   10:  invokevirtual   #4; //Method java/lang/StringBuilder.append:(I)Ljava/lan
g/StringBuilder;
   13:  ldc     #5; //String
   15:  invokevirtual   #6; //Method java/lang/StringBuilder.append:(Ljava/lang/
String;)Ljava/lang/StringBuilder;
   18:  invokevirtual   #7; //Method java/lang/StringBuilder.toString:()Ljava/la
ng/String;
   21:  astore_2
   22:  return

public void bar(){
int intVar = 5;
String strVar = String.valueOf(intVar);
}

This approach invokes simply a static method of String to get the String version of int

public void bar();
  Code:
   0:   iconst_5
   1:   istore_1
   2:   iload_1
   3:   invokestatic    #8; //Method java/lang/String.valueOf:(I)Ljava/lang/Stri
ng;
   6:   astore_2
   7:   return

which in turn calls Integer.toString()

Ask yourself the purpose of the code. Is it to:

Concatenate an empty string with a value
Convert a value to a string

It sounds much more like the latter to me... which is why I'd use String.valueOf. Whenever you can make your code read in the same way as you'd describe what you want to achieve, that's a good thing.

Note that this works for all types, and will return "null" when passed a null reference rather than throwing a NullPointerException. If you're using a class (not an int as in this example) and you want it to throw an exception if it's null (e.g. because that represents a bug), call toString on the reference instead.

String valueOf vs concatenation with empty string

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