1. Introduction

Boolean operators are essential components of programming languages, allowing developers to create logical expressions that evaluate to either true or false. In Java, boolean operators play a crucial role in controlling the flow of program execution, making decisions, and executing conditional statements. In this article, you’ll discover the different boolean operators in Java and learn how to use them in your programs.

2. What is a Boolean Operator?

A boolean operator is a logical operator used in programming to perform logical operations. These operations can apply to non boolean types, but will always return a boolean value. Boolean operators can be divided into four categories: equality operators, comparison operators, conditional operators, and logical operators.

3. Equality Operators

The equality operator is applicable to both primitive and object types.

3.1. Primitive Data Value Equality (== and !=)

The “==” operator determines whether two primitive a and b values are equal, i.e. whether they have the same primitive value.

    int a = 3;
    int b = 20;
    boolean result = a == b; //result is false

The “!=” operator is the opposite of the “==” operator, i.e. it determines whether two primitive values a and b are unequal.

    int a = 3;
    int b = 20;
    boolean result = a != b; //result is true

However, care should be taken when making comparisons involving floating-point numbers. Since these are stored as approximations on a finite number of bits, comparison in the strict sense should be avoided.

    double a = 1.0 - 2.0/3.0;
    double b = 1.0/3.0;
    boolean result = a == b; //result is false

As you can see, the result of the above comparison is “false”. This is mathematically incorrect because 1 – 2/3 = 1/3.
One way to avoid this problem is to define a calculation precision.

    double precision = 1e-10;
    double a = 1.0 - 2.0/3.0;
    double b = 1.0/3.0;
    boolean result = (a - b) < precision; //result is true

3.2. Object Reference Equality (== and !=)

The equality operator on the objects tests not their contents but their respective references. To test the contents of objects, there’s another way, which we’ll see later: the equals() method.
Equality Test(==)

    Student student1 = new Student();//New Object
    Student student2 = new Student();//New Object
    Student student3 = student1;
    boolean result = student3 == student1; //Returns true

Inequality Test(!=)

    Student student1 = new Student();//New Object
    Student student2 = new Student();//New Object
    Student student3 = student1;
    boolean result = student3 != student2; //Returns true

It’s important to note that the equality test is only possible if the objects being compared are cast-compatible.

    Student student1 = new Student();//New Object
    Student student2 = new Student();//New Object
    Student student3 = student1;
    String notStudentCompatible = "This is String cannot be cast to a Student object";
    boolean result = student3 != notStudentCompatible; //Compile-time error

4. Comparison Operators

Relational operators can be summarized in the following table:

All relational operators are binary and operands are numerical expressions.
These operators are nonassociative. This means that the following code will not compile.

        int a = 4, b = 5, c = 9;
        boolean result = a < b < c; //Compile-time error

The code must be rewritten as follows:

        int a = 4, b = 5, c = 9;
        boolean result = a < b && b < c;//Compile-time error

5. Conditional Operators (&& and ||)

In Java, the logical AND (&&) and logical OR (||) operators are used for boolean expressions to combine multiple conditions.

These are short-circuit operators, meaning that the right operand is only evaluated if necessary.
Running the code below will print 0 to the console. This shows that the second condition i++ < 20 was not evaluated.

        int i = 0;
        if(i>1 && i++ < 20){
            doSomething();;
        }
        System.out.println(i);//Prints: 0

Below is a table summarizing the possible values of the result of the operation as a function of the operands a and b.

6. Boolean Logical Operators (&, |, !, and ^)

The operators that fall into this category are: logical complement (!), logical AND, logical inclusive OR, logical exclusive OR also known as XOR.
Let a and b be two Boolean expressions. The table below presents the result of applying the different operators.

Unlike conditional operators, logical operators necessarily evaluate both operands.

        int i = 0;
        if(i>1 & i++ < 20){
            doSomething();
        }
        System.out.println(i);//Prints: 1

The code below will print 1 to the console, meaning that the second expression (i++ < 20) was evaluated even if it was not strictly necessary.

7. Boolean Logical Compound Assignment Operators (&=, |=, and ^=)

There are also compound logical operators on which we will not spend much time. All you need to know can be summarized here:

• a &= b is equivalent to a = a & b
• a |= b is equivalent to a = a | b
• a ^= b is equivalent to a = a ^ b

8. Precedence and Associativity Rules

Relational operators are nonassociative. They have lower precedence than the arithmetic operators, but higher precedence than the assignment operators.
You can read more about Operator Precedence here.

9. Conclusion

You’ve just scratched the surface of boolean operators in Java! These little tools are like magic spells, helping your code compare things and make decisions. Now that you’ve got the hang of them, you can use them to build all sorts of cool stuff.

10. References

1) OCP Oracle Certified Professional Java SE 17 by Khalil A. Mughal and Vasily A. Strelnikov
2) Oracle Java Documentation