Boolean Expressions

This chapter introduces relational and logical operators. It also discusses the use of these operators to write Boolean expressions.

21. NOT!


Answer:

5 > 2 || 12 <= 7
    T  
5 > 2 && 12 <= 7
    F  
3 == 8 || 6 != 6
    F  
3 == 8 && 6 != 6
    F  

NOT!

A
!A
true
false
false
true

The NOT operator in Java is this:   !   (exclamation point). The NOT operator changes true to false and false to true, as seen in the truth table. This may seem like a silly thing to do, but often it is useful. Sometimes it is more natural to express a condition in a particular way, but the program logic calls for the reverse of what you have written. Time for the NOT operator.

Say that you are shopping for new shoes. You are only interested in shoes that cost less than $50. Here is a program fragment:

if (  ______(cost < 50)  )
System.out.println("Reject these shoes");
else
System.out.println("Acceptable shoes");

Question 22:

Fill in the blank so that the program fragment rejects shoes that do not cost less than $50.