Question

When adding 'a' + 'b' it produces 195. Is the output datatype char or int?

Answer 1

The result of adding Java chars, shorts, or bytes is an int:

Java Language Specification on Binary Numeric Promotion:

• If any of the operands is of a reference type, unboxing conversion
  (§5.1.8) is performed. Then:
• If either operand is of type double, the
  other is converted to double.
• Otherwise, if either operand is of type
  float, the other is converted to float.
• Otherwise, if either operand
  is of type long, the other is converted to long.
• Otherwise, both
  operands are converted to type int.

But note what it says about compound assignment operators (like +=):

The result of the binary operation is converted to the type of the left-hand variable … and the result of the conversion is stored into the variable.

For example:

char x = 1, y = 2;
x = x + y; // compile error: "possible loss of precision (found int, required char)"
x = (char)(x + y); // explicit cast back to char; OK
x += y; // compound operation-assignment; also OK

One way you can find out the type of the result, in general, is to cast it to an Object and ask it what class it is:

System.out.println(((Object)('a' + 'b')).getClass());
// outputs: class java.lang.Integer

If you’re interested in performance, note that the Java bytecode doesn’t even have dedicated instructions for arithmetic with the smaller data types. For example, for adding, there are instructions iadd (for ints), ladd (for longs), fadd (for floats), dadd (for doubles), and that’s it. To simulate x += y with the smaller types, the compiler will use iadd and then zero the upper bytes of the int using an instruction like i2c (“int to char”). If the native CPU has dedicated instructions for 1-byte or 2-byte data, it’s up to the Java virtual machine to optimize for that at run time.

If you want to concatenate characters as a String rather than interpreting them as a numeric type, there are lots of ways to do that. The easiest is adding an empty String to the expression, because adding a char and a String results in a String. All of these expressions result in the String "ab":

• 'a' + "" + 'b'
• "" + 'a' + 'b' (this works because "" + 'a' is evaluated first; if the "" were at the end instead you would get "195")
• new String(new char[] { 'a', 'b' })
• new StringBuilder().append('a').append('b').toString()
• String.format("%c%c", 'a', 'b')