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Int Promotion

Binary arithmetic operations (+, %, etc.) using byte, short, and char always promote the operands to ints, even if neither of the operands is an int.

  • For example, this will not compile: 

    short s1 = 5;
short s2 = 1;

short s3 = s1 + s2;  // COMPILER ERROR: Type mismatch: cannot convert from int to short

  • Instead, we store the value of s1 + s2 in an int variable.

short s1 = 5;
short s2 = 1;

int iResult = s1 + s2;

However, Java is smart enough to use two int constants in a binary arithmetic operation without having to promote.

  • The code below will compile because the compiler can see the result will fit into a short. 
    short sResult = 5 / 2;

Compound Assignment Operators

The compound assignment operators (+=, *=, etc.) do not promote operands, so they allow us to do arithmetic.

We know this statement would not work.

  • We cannot assign the int value yielded by + to a byte. 
    byte b = 12;
int i = 15;
b = b + i; // DOES NOT COMPILE

However, we can add an int to a byte and assign to that byte with the += operator. 

byte b = 12;
int i = 15;
b += i;

Drill

CastingDataTypes/com.example.casting.drills.Division * Follow the instructions, adding your expected results where prompted. When you finish, check the solution for explanations.

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