Logic for Binary numeric promotion

Question

Please explain me the logic for binary numeric promotion on the below code.

boolean flag = 'A' < 'a';
System.out.println(flag);// prints true.

Answer 1

In Java, the char primitive data type was defined as a 16-bit Unicode character, with values in the hexadecimal range from 0x0000 to 0xFFFF . When you compare two char values, it's that 16-bit hex value that's used.

In your specific case, A is represented by 0x0041 and a by 0x0061 , so 'A' < 'a' will evaluate to true .

For reference: Unicode (The Java Tutorials)

Answer 2

It's called promotion when you are comparing two different types (usually numbers) and one of them will be converted to the other so they can be compared. like:

int x = 5;
double y = 6;
if (x < y)
    ...

In Java int and double can be compared. In that case, int will be converted to double implicitly.

In your case there is no promotion. A character stored in memory as a number (in Java it's based UTF-16 standard and stored as exactly 2 bytes like a short ) and in 'A' < 'a' integer numbers are compared.