String valueOf vs concatenation with empty string

Question

I am working in Java code optimization. I'm unclear about the difference between String.valueOf or the +"" sign:

int intVar = 1; String strVar = intVar + ""; String strVar = String.valueOf(intVar); 

What is the difference between line 2 and 3?

Answer 1

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()