1.5 Compound Assignment Operators

Compound assignment operators are shortcuts that do a math operation and assignment in one step. For example, x += 1 adds 1 to the current value of x and assigns the result back to x. It is the same as x = x + 1.

Increment and Decrement Operators

Since changing the value of a variable by one is especially common, there are two extra concise operators ++ and --, also called the plus-plus or increment operator and minus-minus or decrement operator that set a variable to one greater or less than its current value.

Thus x++ is an even more concise way to write x = x + 1 than the compound operator x += 1. You'll see this shortcut used a lot in loops when we get to them in Unit 4. Similarly, y-- is a more concise way to write y = y - 1.

Compound Operators Table

Here's a table of all the compound arithmetic operators and the extra concise increment and decrement operators and how they relate to fully written out assignment expressions:

Note on Prefix and Postfix Operators

If you look at real-world Java code, you may occasionally see the ++ and -- operators used before the name of the variable, like ++x rather than x++. That is legal but not something that you will see on the AP exam.

Putting the operator before or after the variable only changes the value of the expression itself. If x is 10 and we write, System.out.println(x++) it will print 10 but afterwards x will be 11. On the other hand if we write, System.out.println(++x), it will print 11 and afterwards the value will be 11.

The AP exam will never use the prefix form of these operators nor will it use the postfix operators in a context where the value of the expression matters.