9. Java Conditionals (If-else and Switch-case) Statements

 

Java Conditionals

Java conditionals statements execute a particular section of code for a specific condition. If a specific condition is specified then only the particular code under its segment will be executed. Java has the following conditional statements:

1. Use if to specify a block of code to be executed, if a specified condition is true.
2. Use else to specify a block of code to be executed, if the same condition is false.
3. Use else if to specify a new condition to test, if the previous condition is false.
4. Use switch to specify many alternative blocks of code to be executed.

If-else Statement

• The if-else statement is used to perform two operations for a single condition.
• The if-else statement is an extension to the statement using which we can perform two different operations.
• One operation is for the correctness of that condition and other is for the incorrectness of that condition.

Control flow for if-else statement

import java.util.Scanner;

class IfElse {

    public static void main(String[] arr) {

        System.out.print("Enter your age: ");

        Scanner input = new Scanner(System.in);

        int age = input.nextInt();

        if (age > 18) {

            System.out.println("Yooo!!! You can drive.");

        } else {

            System.out.println("Nooo!!! You can't drive yet.");

        }

    }

}

Outputs :

Enter your age: 20
Yooo!!! You can drive.

Enter your age: 18
Nooo!!! You can't drive yet.

If-else Ladder

• Instead of using multiple if statements, we can also use else if along with if thus forming an if else-if else ladder.
• The else-if ladder statement is an extension of the if-else statement.
• It is used in the scenario where there are multiple cases to be performed for different conditions.
• Last else is executed only if all the previous conditions fails.
• The last else block is optional.
• Using such kind of logic reduces indents.

Control flow for if else-if ladder

import java.util.Scanner;

class IfElseLadder {

    public static void main(String[] arr) {

        System.out.print("Enter your percentage: ");

        Scanner input = new Scanner(System.in);

        double marks = input.nextDouble();

        if (marks >= 90) {

            System.out.println("You got grade A.");

        } else if(marks >= 80){

            System.out.println("You got grade B.");

        } else if(marks >= 65){

            System.out.println("You got grade C.");

        } else if(marks >= 50){

            System.out.println("You got grade D.");

        }else{

            System.out.println("You are fail.");

        }

input.close();

    }

}

Outputs :

Enter your percentage : 95.6
You got grade A.

Enter your percentage : 87.4
You got grade B.

Enter your percentage : 70
You got grade C.

Enter your percentage : 57
You got grade D.

Enter your percentage : 45.9
You are fail.

Switch-Case

• The switch-case statement is an alternate to if else-if ladder statement.
• Switch-case statement is allows us to execute multiple operations for the different values of a single variable called switch variable.
• We can define various statements in the multiple cases for the different values of a single variable.
• The switch variable can be an integer, character or string type in Java.
• The case value can be used only inside the switch statement.
• The break statement in switch case is not necessary. It is optional.
• If there is no break statement found in the matched case, all the cases will be executed present after the matched case.
• The default case is also optional. The default case is executed when all the other cases are false.

Control flow for switch-case statement

import java.util.Scanner;

class SwitchCase {

    public static void main(String[] arr) {

        System.out.print("Choose a base among 2, 8, 10, 16: ");

        Scanner input = new Scanner(System.in);

        int base = input.nextInt();

        switch (base) {

            case 2:

                System.out.println("The number system is BINARY.");

                break;

            case 8:

                System.out.println("The number system is OCTADECIMAL.");

                break;

            case 10:

                System.out.println("The number system is DECIMAL.");

                break;

            case 16:

                System.out.println("The number system is HEXADECIMAL.");

                break;

            default:

                System.out.println("The choice is not valid.");

                break;

        }

        System.out.print("Thanks for viewing my Java Code!!!");

input.close();

    }

}

Outputs :

Choose a base among 2, 8, 10, 16 : 2
The number system is BINARY.
Thanks for viewing my Java Code!!!

Choose a base among 2, 8, 10, 16 : 8
The number system is OCTADECIMAL.
Thanks for viewing my Java Code!!!

Choose a base among 2, 8, 10, 16 : 10
The number system is DECIMAL.
Thanks for viewing my Java Code!!!

Choose a base among 2, 8, 10, 16 : 16
The number system is HEXADECIMAL.
Thanks for viewing my Java Code!!!

Choose a base among 2, 8, 10, 16 : 20
The choice is not valid.
Thanks for viewing my Java Code!!!

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