sum = 42 - 12 ;

Expressions

Normally you would say:

The statement puts 30 into sum.

However, this is a little sloppy. Sometimes when the expression is complicated you need to think carefully about the two steps.

An expression is a combination of literals, operators, variable names, and parentheses used to calculate a value.

This (slighly incomplete) definition needs some explanation:

• literal — characters that directly mean a value, like: 3.456
• operator — a symbol like plus + or times * that asks for an arithmetic operation.
• variable — a section of memory containing a value.
• parentheses — ( and ).

This might sound awful. Actually, this is stuff that you know from algebra, like:

(32 - y) / ( x + 5 )

In the above, the character / means division. Not just any mess of symbols will work. The following

32 - y) / ( x  5 + )

is not a syntactically correct expression. There are rules for this, but the best rule is that an expression must look OK as algebra. However, multiplication must always be shown by using a * operator. You can't multiply two variables by placing them next to each other. So, although xy might be correct in algebra, you must use x*y in Java.