Arithmetic Operators

 

Something we commonly must do in our programs is perform arithmetic operations. Java provides three basic categories of operators for performing math operations. They're the basic operators, like add, subtract, multiply, and divide, what are called prefix and postfix operators, and then what are called compound assignment operators. The basic math operators are just what you would expect, things like add, subtract, multiply, and divide. The operators we use for these are, again, things that are very familiar. If I'm adding, I use a plus sign. And when I do things like add, it doesn't really matter whether I'm using a floating point or an integer. So, if I say 1 + 2, the answer is going to be 3. For subtraction, we use the minus sign. Again, it doesn't really matter whether we're using floating point or integers. If I subtract 4 from 5, I get 1. If we multiply, we use an asterisk, 4 * 2 is 8. And all that stuff is straightforward. As we get to the divide operations, though, there are some differences between floating point and integer. If I take 13.0 and divide it by 5.0, that's a floating-point operation. Floating points have fractions, so I will get 2.6. But now if I take the integer 13 divided by 5, that's an integer operation. Integers don't have fractions, so I'll get just 2. It doesn't matter what the fractional portion would be. It's just dropped. There's no rounding or anything. It's just the whole number of times that you can do the division. So, 5 goes into 13 two whole times. There's another operator called the modulus operator, also known as the remainder operator, and that gives you the remainder of the divide. So, let's look at the integer first on this one. If I say 13 % 5, that's the percent symbol, my answer will be 3. Five goes into 13 two whole times, leaving 3, 5 * 2 is 10, subtract 10 from 13, you get 3. And you can do a modulus on floating points as well. So, if I do 13.0 % 5.0, I'll have a remainder of 3.0. As we look at the prefix and postfix operators, they allow us to operate directly on a value. The ++ symbol is the increment. It increments a value by 1. The ‑‑ symbol decrements a value by 1. So, if you look here, if I have a variable, myVal, and I set it to 5, if I say print out ++myVal, that's the increment operator. Because it's before the actual variable, the ++ is before the variable, that's a prefix, which means that the operation is applied before we get the value back. So, the result of this print statement is 6, the 5 was incremented, so we print out it was 6. If I print myVal again, it's still 6. But now if I move the operator after the variable, it's now a postfix operator. And what that means is that I get the value back, and then the operation is performed. So, if I look at similar code here where I have my variable, myVal, I set it to 5, but this time when I print it out, I say myVal++, so I'm doing a postfix increment. The value printed will be 5 because that 5 was returned. But myVal is now incremented. If I print myVal now, I will get 6. The last category of math operators is what we call compound assignment operators. And what these do is they combine an operation and the assignment. So, basically, it looks at the right side of the operator, takes whatever that is, and applies the operation to the left side, and then stores the value into the left side. So, let's see what that looks like. If I go ahead and have myVal, and I set it equal to 50, if I say myVal ‑= 5, so the right hand side's value is 5, the left hand side value is currently 50, it applies the operation, which is the minus sign, so it subtracts 5 from 50, and then stores that value back into myVal. So, if I print out myVal, myVal has 45. And they're available for all five basic math operations. In my experience, I use the ‑= and the += far and away the most, but you do find occasions to use the other ones as well. So looking at another example, if I have an int result = 100, and I have 2 more variables, val1 = 5 and val2 = 10, if I now say result /= val1 * val2, remember that it's going to take the complete result of the right side. So, if I look a val1 * val2, the result of 5 * 10 is 50. It then takes the existing value in result, which in this case is 100, and then it then takes that operator, the divide, and performs that operation between them. So, it's going to divide 100 by 50 and then store that back into our variable called result. So, we print out the value of 2.