What Is an Expression?
By the end of this lesson, you'll be able to:
- Define "expression" and distinguish it from a statement
- Identify expressions inside a line of Apex code
- Explain that every expression evaluates to a single value
Prerequisites: Module 3: "Programming Basics: Variables & Data"
Expressions vs. statements
Integer total = 4 + 3;4 + 3 is an expression — it evaluates to a single value, 7. The whole line, Integer total = 4 + 3;, is a statement — a complete instruction that does something (here, declares a variable and stores the expression's result in it).
Every expression, however complicated, boils down to one value once Apex finishes evaluating it.
Expressions can nest inside each other
Integer result = (4 + 3) * 2;4 + 3 is an expression. (4 + 3) * 2 is a bigger expression, built out of the first one. This is exactly how the rest of this module works: small operators combine into bigger, more useful expressions.
Common mistakes
- Thinking a variable name alone isn\'t an expression. It is —
totalby itself evaluates to whatever value it currently holds, which is whySystem.debug(total);works at all.
Exercise
Write down three different expressions that would each evaluate to the number 10 (for example, 5 + 5). Try to make them structurally different from each other.
Show hint
Addition, multiplication, and subtraction can all reach 10 in different ways: 5+5, 2*5, 20-10.
What Is an Expression? Quiz
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Summary
An expression is any piece of code that evaluates down to a single value — a number, a piece of text, true or false. Every operator you'll meet in this module exists to combine expressions into bigger ones.