Numeric Promotion Rules - OCA Review Notes

4 Numeric Promotion Rules

Numeric Promotion Rules

1. If two values have different data types, Java will automatically promote one of the val- ues to the larger of the two data types.
2. If one of the values is integral and the other is floating-point, Java will automatically promote the integral value to the floating-point value’s data type.
3. Smaller data types, namely byte , short , and char , are first promoted to int any time they’re used with a Java binary arithmetic operator, even if neither of the operands is int .
4. After all promotion has occurred and the operands have the same data type, the result- ing value will have the same data type as its promoted operands.

Rule 1.

	int num =1; // default int
	long longNum = 23L; // long Literal

	// rule 1 -> promote values to larger data type
	long imLong = num + longNum; 

If same datatype -> resulting value will have same datatype.

	float num1= 2300000000F;
	float num2= 55000000000000F;
	float num3 = num1 * num2;

Rule 2.

floating value and integral value operation promotion

	long longNum = 23; // integral
	float floatNum= 1000F; // floating
	//promote longNum value to floating point value's data type(float in this case).
	float z = longNum * floatNum; 

Rule 3.

	byte byteNum= 5;
	short shortNum = 2;

	// both will be promoted to int first before the actual operation.
	int result = byteNum * shortNum; 

• even if you cast those datatype to short,byte,char it will still be promoted to int before performing operation. therefore return type will always be int. except adding parenthesis and cast

	byte byteNum= 5;
	short shortNum = 2;
	
	// both will be promoted to int first before the actual operation.
	int result = (short)byteNum * (short)shortNum; 

	// compile time error lossy conversion
	short shortResult = (short)byteNum * (short)shortNum;

• cast if you want short data type *

	byte byteNum= 5;
	short shortNum = 2;

	// after promotion to int and returning int. we can now cast it to short
	short result = (short) (byteNum * shortNum); 

Rule 4. ( after promotion of operands resulting value is same type.

• All samples above, the resulting value has same datatype with the variable declared on left side*