BEI - Compound Boolean Expressions (Lesson)
Compound Boolean Expressions
Introduction
It is often necessary to check more than one condition in an if statement. In our previous lessons we learned how to use a boolean condition to decide whether to execute code or not. Each time we only checked one condition. What if there were more conditions to check?
Using our grades example, how can you write code to print the letter grades without using nested if statements or if-else-if statements?
A: >= 90
B: <90 and >= 80
C: <80 and >= 75
Logic Operators
When creating boolean expressions it may be necessary to compare more than one expression. We can do this by using logic operators. Logic operators that are in the same line of code have an order of precedence.
Logic operators should be executed in the following order:
| !-Not | Changes the truth value |
| && - And | True when both values are true |
| || - Or | True when one of the values is true |
Short Circuit
Short circuit is when you have two boolean expressions and the left-hand operand is enough to determine whether the statement is true or false. The statement short circuits because it never evaluates the right hand.
Since x is less than 4 and this is an or statement, there is no need to evaluate whether (x != 2) is true or not.
In an AND statement, both expressions must be true for the whole thing to be true. Since the first part of the boolean expression (7 == 5) is false, we do not need to check the second boolean expression. This is a short circuit. The second expression is never checked.
Click on "Runestone Academy" below to open the required reading that is listed.
Runestone Academy: AP CSA – Java Review Links to an external site.:
READ: 5.3 – Complex Conditionals
Click on "Introduction to Computer Science Using Java" below to open the required reading that is listed.
Introduction to Computer Science Using Java Links to an external site.:
READ: Chapter 18: Boolean Expressions
Complete the Review and Flashcards for practice.
Logic Operators Practice
Click below to start the Logic Operators Activity.
Logic Operators Problets Practice
- Click HERE. Links to an external site.
- Click on Topics
- Choose Topic: Logical Expressions, Language: Java
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