Logical Operators

A comparison answers one question at a time. Logical operators let you combine several Boolean answers into a single result. Apex has three of them: AND (&&), OR (||) and NOT (!).

AND, OR and NOT

• && produces true only when BOTH sides are true.
• || produces true when AT LEAST ONE side is true.
• ! flips a Boolean value: !true is false and !false is true.

Boolean sunny = true;
Boolean warm = false;

System.debug(sunny && warm); // false - both must be true
System.debug(sunny || warm); // true  - one true side is enough
System.debug(!warm);         // true  - NOT flips the value

Truth Table Quick Reference

System.debug(true && true);   // true
System.debug(true && false);  // false
System.debug(false || true);  // true
System.debug(false || false); // false
System.debug(!false);         // true

Combining Comparisons

The real power comes from combining comparison results into one expression:

Integer age = 25;
Boolean hasLicense = true;
Boolean canRentCar = age >= 21 && hasLicense; // true

Short-Circuit Evaluation

Apex evaluates a logical expression from left to right and stops as soon as the answer is certain. If the left side of && is false, the whole expression must be false, so the right side never runs. If the left side of || is true, the right side never runs. This is called short-circuit evaluation, and it is a handy way to guard against errors:

List<Integer> numbers = new List<Integer>();
// numbers[0] never runs because the left side is false
Boolean startsWithTen = !numbers.isEmpty() && numbers[0] == 10;
System.debug(startsWithTen); // false, and no error is thrown