Why is String Concatenation for Integer-to-String Conversion in Java Considered Unconventional?

Converting Integers to Strings in Java: Unconventional Practices

When converting an integer to a string in Java, the conventional approach involves using either Integer.toString(int) or String.valueOf(int) methods. However, a peculiar approach that has been observed is the use of string concatenation, as seen in the following code snippet:

int i = 5;
String strI = "" + i;

Such methods are unconventional and might indicate a lack of knowledge about proper techniques in Java. Though this concatenation method may work, it is an uncommon practice.

Delving deeper into how Java handles this concatenation, the compiler optimizes and translates such code into a series of string appends, as demonstrated below:

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

While this method is slightly less performant due to the use of StringBuilder.append() and Integer.getChars(), it still achieves the desired result.

It is important to note that the compiler does not optimize the empty string concatenation, as evident from the bytecode analysis below:

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

This has led to a proposal and ongoing development to change such behavior in JDK 9. Therefore, it is recommended to use standard methods like Integer.toString(int) or String.valueOf(int) for clarity and maintainability when converting integers to strings in Java.

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