Boolean Operators

To allow programs to make decisions, we must use the combination of Boolean operators and if statements (Future Lesson).

These operators are binary operators that require a LEFT OPERAND and a RIGHT OPERAND. The operator will produce a Boolean result of true or false.

Comparison Operators

These operators compare the left and the right operand and return true if the condition is satisfied.

let x be a variable and y be a variable that contains comparable values

Operation
Description

x == y

Checks if the values of two operands are equal, if YES: returns true.

x != y

Checks if the values of two operands are not equal to each other, if YES: returns true.

x > y

Checks if the LEFT operand is greater than the RIGHT operand, if YES: returns true.

x < y

Checks if the LEFT operand is less than the RIGHT operand, if YES: returns true.

x >= y

Checks if the LEFT operand is greater than OR equal to the RIGHT operand, if YES: returns true.

x <= y

Checks if the LEFT operand is less than OR equal to the RIGHT operand, if YES: returns true.

All the operation above return false if the condition is not met.

Logical Operators

Logical Operators are used to combine boolean expressions.

Logical AND Operator: &&

In Java, multiple boolean expressions can be combined by the && operator.

This operator returns true if both sides of the operands evaluate to true. Otherwise it will be false.

Example Use of the AND operator:

If the train is late to the station AND there are no cabs at the station, I am late to work.

Their are two boolean conditions:
1. Train is late or not late
2. There are not cabs

The person being late is dependent on BOTH conditions being TRUE. 

The two conditions are combined by a Logical AND operation.

Logical OR Operator: ||

In Java, multiple boolean expressions can be combined by the || operator.

This operator returns true if both sides OR either sides of the operands evaluate to true. It only returns false if both sides of the operands evaluated to false.

Example Use of the OR operator:

I only snack if I am hungry OR if I am bored.

Their are two boolean conditions:
1. Person is hungry
2. Person is bored

The person being late is dependent on EITHER conditions being TRUE OR BOTH conditions being true.

The two conditions are combined by a Logical OR operation.

Logical NOT Operator: !

In Java, ! is used to reverse a boolean expression's boolean result.

Operation
Result

!(true)

false

!(false)

true

Example Use of the NOT operator:

If it is NOT a weekday, I don't go to school

The person is dependent on not going to school when it is not a weekday.

On Monday to Friday, the condition of being a weekday is true
    --> Therefore, the "NOT weekday" evaluates to false hench they go to school.

On Saturday & Friday, the condition being a weekday is false
    --> Therefore, the "NOT weekday" evaluates to true hence they don't go to school.

Code Examples on Java

class Main {
    public static void main(String[] args) {
        System.out.println("Boolean Operations in Java.");

        int x = 10;
        int y = 15;

        System.out.println("Is x == y?: " + (x == y));
        System.out.println("Is x != y?: " + (x != y));
        System.out.println("Is x > y?: " + (x > y));
        System.out.println("Is x < y?: " + (x < y));
        System.out.println("Is x >= y?: " + (x >= y));
        System.out.println("Is x <= y?: " + (x <= y));

        int grade = 10;
        int average = 81;

        System.out.println("Are you in grade 10 and have an average higher than or equal to 80?: " + (grade == 10 && average >= 80));

        String fav_fruit = "blueberry";
        System.out.println("Is your favourite fruit blueberry or kiwi?: " + (fav_fruit == "blueberry" || fav_fruit == "kiki"));
        
        boolean weekday = true;
        System.out.println("Do you not go to school today?: " + (!(weekday)));
        
    }
}

SOURCES

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