Logical Expressions

In this lesson, an explanation of the use of logical expressions in Java programs is provided.

We'll cover the following...

Introduction
Comparative operators
Boolean operators

Introduction

Logical expressions are also known as Boolean expressions. It will always evaluate to a value of either true or false. Therefore, they will be represented by the data type boolean. While they may seem similar to mathematical operators, the difference lies in how they are used with comparative or boolean operators. Let’s look at both types of operators in detail.

Comparative operators

Java has several operators that can be used to compare value. Comparison implies knowing which value is greater than the other, or equal to it, and so on. The table below shows the entire list of operators available in Java.

Symbols	Comparative operators
<	Less than
>	Greater than
<=	Less than or equal to
>=	Greater than or equal to
==	Equal to
!=	Not equal to

Java

class log_op {
    public static void main(String[] args) {
        int x = 5;
        int y = 10;
        System.out.println("x is equal to: " + x);
        System.out.println("y is equal to: " + y);
        System.out.println("x is greater than y");
        System.out.println(x > y);
        System.out.println("x is less than y");
        System.out.println(x < y);
        System.out.println("x is greater than or equal to y");
        System.out.println(x >= y);
        System.out.println("y is less than or equal to y");
        System.out.println(y <= y);
        System.out.println("x is equal to y");
        System.out.println(x == y);
        System.out.println("x is not equal to y");
        System.out.println(x != y);
    }
}

Boolean operators

These operators rely on boolean algebra. Hence, boolean operators will work directly on boolean values. There are four types of boolean operators. Let’s first look at their symbols and what they are in the table below before we discuss what functionality they perform.

Symbols	Boolean operators
!	Boolean NOT
&&	Boolean AND
\|\|	Boolean OR
^	Boolean exclusive XOR

The boolean NOT inverts the value of the boolean expression that follows it.
The boolean AND will return true if and only if, expressions on both sides of the operator are true.
The boolean OR will return true if the expression on either or both sides of the operator is true.
The boolean exclusive XOR will return true if one of the expressions evaluates to true and the other to false.

Now that we have some understanding of these operators let’s see how to use them in code.

Java

class bool_ops {
    public static void main(String[] args) {
        boolean x = true;
        boolean y = false;
        System.out.println("Value of x: " + x);
        System.out.println("Value of y: " + y);
        System.out.println("Boolean NOT of x");
        System.out.println(!x);
        System.out.println("Boolean AND of x and y");
        System.out.println(x && y);
        System.out.println("Boolean OR of x and y");
        System.out.println(x || y);
        System.out.println("Boolean exclusive XOR of x and y");
        System.out.println(x ^ y);
    }
}

Let’s assess our understanding of this lesson with the following question:
Question:
Evaluate the following complex logical expression involving both boolean and comparative operators:
$(10 > 5 \, \text{||} \, (15 \leq 20 \, \&\& \, 7 \neq 7)) \, \&\& \, (true \, == \, false)$
Provide the correct result by applying the rules of both boolean and comparative operator precedence, taking into account the effect of the parentheses.
Note: Write your answer in the space provided below.