# 3.8. Unit 3 - Summary¶

In this chapter you learned about conditionals. Conditionals are used to execute code when a Boolean expression is true or false. A Boolean expression is one that is either true or false like `x > 0`.

## 3.8.2. Concept Summary¶

• Block of statements - One or more statements enclosed in an open curly brace ‘{‘ and a closing curly brace ‘}’.

• Boolean expression - A mathematical or logical expression that is either true or false.

• complex conditional - A Boolean expression with two or more conditions joined by a logical and ‘&&’ or a logical or ‘||’.

• conditional - Used to execute code only if a Boolean expression is true.

• DeMorgan’s Laws - Rules about how to distribute a negation on a complex conditional.

• logical and - Used to only execute the following statement or block of statements if both conditions are true

• logical or - Used to execute the following statement or block of statements if one of the conditions are true

• negation - turns a true statement false and a false statement true

• short circuit evaluation - The type of evaluation used for logical and ‘&&’ and logical or ‘||’ expressions. If the first condition is false in a complex conditional with a logical and the second condition won’t be evaluated. If the first condition is true is a complex conditional with a logical or the second condition won’t be evaluated.

## 3.8.3. Java Keyword Summary¶

• if (Boolean expression) - used to start a conditional statement. This is followed by a statement or a block of statements that will be executed if the Boolean expression is true.

• else - used to execute a statement or block of statements if the Boolean expression on the if part was false.

• else if (Boolean expression) - used to have 3 or more possible outcomes such as if x is equal, x is greater than, or x is less than some value. It will only execute if the condition in the ‘if’ was false and the condition in the else if is true.

For more practice, see this Quizlet.

## 3.8.4. Common Mistakes¶

• Using = instead of == in `if`’s. Remember that = is used to assign values and == is used to test. Ifs always use ==.

• Putting a ; at the end of `if (test);`. Remember that the if statement ends after `if (test) statement;` or use curly brackets `if (test) { statements; }`.

• Using two `if`’s one after the other instead of an `if` and `else`.

• Trouble with complex conditionals which are two or more Boolean expressions joined by `&&` or `||`.

• Not understanding that || is an inclusive-or where one or both conditions must be true.

• Trouble with understanding or applying negation (`!`). See the section on DeMorgan’s Laws.

• Not understanding short circuit evaluation which is that if evaluation of the first Boolean expression is enough to determine the truth of a complex conditional the second expression will not be evaluated.