Java Tutorial 9: Operators-Equality, Relational, and Conditional Operators

The Equality and Relational Operators

The equality and relational operators determine if one operand is greater than, less than, equal to, or not equal to another operand. The majority of these operators will probably look familiar to you as well. Keep in mind that you must use "==", not "=", when testing if two primitive values are equal.

==      equal to

!=      not equal to

>       greater than

>=      greater than or equal to

<       less than

<=      less than or equal to

The following program, ComparisonDemo, tests the comparison operators:

class ComparisonDemo {

    public static void main(String[] args){

        int value1 = 1;

        int value2 = 2;

        if(value1 == value2)

            System.out.println("value1 == value2");

        if(value1 != value2)

            System.out.println("value1 != value2");

        if(value1 > value2)

            System.out.println("value1 > value2");

        if(value1 < value2)

            System.out.println("value1 < value2");

        if(value1 <= value2)

            System.out.println("value1 <= value2");

    }

}

Output:

value1 != value2

value1 <  value2

value1 <= value2

The Conditional Operators

The && and || operators perform Conditional-AND and Conditional-OR operations on two boolean expressions. These operators exhibit "short-circuiting" behavior, which means that the second operand is evaluated only if needed.

&& Conditional-AND

|| Conditional-OR

The following program, ConditionalDemo1, tests these operators:

class ConditionalDemo1 {

    public static void main(String[] args){

        int value1 = 1;

        int value2 = 2;

        if((value1 == 1) && (value2 == 2))

            System.out.println("value1 is 1 AND value2 is 2");

        if((value1 == 1) || (value2 == 1))

            System.out.println("value1 is 1 OR value2 is 1");

    }

}

Another conditional operator is ?:, 

which can be thought of as shorthand for an if-then-else statement (discussed in the Control Flow Statements section of this lesson). This operator is also known as the ternary operator because it uses three operands. In the following example, this operator should be read as: "If someCondition is true, assign the value of value1 to result. Otherwise, assign the value of value2 to result."

The following program, ConditionalDemo2, tests the ?: operator:

class ConditionalDemo2 {

    public static void main(String[] args){

        int value1 = 1;

        int value2 = 2;

        int result;

        boolean someCondition = true;

        result = someCondition ? value1 : value2;

        System.out.println(result);

    }

}

Because someCondition is true, this program prints "1" to the screen. Use the ?: operator instead of an if-then-else statement if it makes your code more readable; for example, when the expressions are compact and without side-effects (such as assignments).

The Type Comparison Operator instanceof

The instanceof operator compares an object to a specified type. You can use it to test if an object is an instance of a class, an instance of a subclass, or an instance of a class that implements a particular interface.

The following program, InstanceofDemo, defines a parent class (named Parent), a simple interface (named MyInterface), and a child class (named Child) that inherits from the parent and implements the interface. (Don't worry if you can't understand everything, we'll comeback to this later).

class InstanceofDemo {

    public static void main(String[] args) {

        Parent obj1 = new Parent();

        Parent obj2 = new Child();

        System.out.println("obj1 instanceof Parent: "

            + (obj1 instanceof Parent));

        System.out.println("obj1 instanceof Child: "

            + (obj1 instanceof Child));

        System.out.println("obj1 instanceof MyInterface: "

            + (obj1 instanceof MyInterface));

        System.out.println("obj2 instanceof Parent: "

            + (obj2 instanceof Parent));

        System.out.println("obj2 instanceof Child: "

            + (obj2 instanceof Child));

        System.out.println("obj2 instanceof MyInterface: "

            + (obj2 instanceof MyInterface));

    }

}

class Parent {}

class Child extends Parent implements MyInterface {}

interface MyInterface {}

Output:

obj1 instanceof Parent: true

obj1 instanceof Child: false

obj1 instanceof MyInterface: false

obj2 instanceof Parent: true

obj2 instanceof Child: true

obj2 instanceof MyInterface: true

When using the instanceof operator, keep in mind that null is not an instance of anything.

Summary of Operators

The following quick reference summarizes the operators supported by the Java programming language.

Simple Assignment Operator

=       Simple assignment operator

Arithmetic Operators

+       Additive operator (also used for String concatenation)

-       Subtraction operator

*       Multiplication operator

/       Division operator

%       Remainder operator

Unary Operators

+       Unary plus operator; indicates positive value (numbers are positive without this, however)

-       Unary minus operator; negates an expression

++      Increment operator; increments a value by 1

--      Decrement operator; decrements a value by 1

!       Logical complement operator; inverts the value of a boolean

Equality and Relational Operators

==      Equal to

!=      Not equal to

>       Greater than

>=      Greater than or equal to

<       Less than

<=      Less than or equal to

Conditional Operators

&&      Conditional-AND

||      Conditional-OR

?:      Ternary (shorthand for if-then-else statement)

Type Comparison Operator

instanceof      Compares an object to a specified type