How do I convert from int to String?

Normal ways would be Integer.toString(i) or String.valueOf(i).

The concatenation will work, but it is unconventional and could be a bad smell as it suggests the author doesn't know about the two methods above (what else might they not know?).

Java has special support for the + operator when used with strings (see the documentation) which translates the code you posted into:

StringBuilder sb = new StringBuilder();sb.append("");sb.append(i);String strI = sb.toString();

at compile-time. It's slightly less efficient (sb.append() ends up calling Integer.getChars(), which is what Integer.toString() would've done anyway), but it works.

To answer Grodriguez's comment: ** No, the compiler doesn't optimise out the empty string in this case - look:

simon@lucifer:~$ cat TestClass.javapublic class TestClass {  public static void main(String[] args) {    int i = 5;    String strI = "" + i;  }}simon@lucifer:~$ javac TestClass.java && javap -c TestClassCompiled from "TestClass.java"public class TestClass extends java.lang.Object{public TestClass();  Code:   0:    aload_0   1:    invokespecial    #1; //Method java/lang/Object."<init>":()V   4:    returnpublic static void main(java.lang.String[]);  Code:   0:    iconst_5   1:    istore_1

Initialise the StringBuilder:

   2:    new    #2; //class java/lang/StringBuilder   5:    dup   6:    invokespecial    #3; //Method java/lang/StringBuilder."<init>":()V

Append the empty string:

   9:    ldc    #4; //String   11:    invokevirtual    #5; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;

Append the integer:

   14:    iload_1   15:    invokevirtual    #6; //Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;

Extract the final string:

   18:    invokevirtual    #7; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;   21:    astore_2   22:    return}

There's a proposal and ongoing work to change this behaviour, targetted for JDK 9.

It's acceptable, but I've never written anything like that. I'd prefer this:

String strI = Integer.toString(i);

It's not a good way.

When doing conversion from int to string, this should be used:

int i = 5;String strI = String.valueOf(i);