Selection Statement in Java

Selection statements in Java are control flow statements that allow you to make decisions in your Code based on certain conditions. These statements enable your Java programs to execute different blocks of Code depending on whether specific conditions are true or false. Selection statements are fundamental to programming, allowing you to create dynamic, flexible, and responsive applications.

There are three main types of selection statements in Java:

1. if Statement:

The "if" statement is an essential component of programming that enables conditional execution of instructions based on a specified condition. The "if" statement assesses a specified condition, executing a predefined set of commands when the condition is true and skipping them otherwise. Essentially, it functions as a way to pose a question in code and generate a corresponding response based on the condition's evaluation.

Syntax:

if (condition) {
    //Code is being executed if the condition is true
}

Condition: An expression that evaluates to a boolean value (true or false).
If the condition is true, the Code inside the curly braces {} is executed.
If the condition is false, the Code inside the curly braces is skipped, and the program continues with the following statement after the if block

Filename: NumberClassifier.java

// Defining a class named NumberClassifier to classify user-entered numbers
public class NumberClassifier {
    public static void main(String[] args) {
        int number = 5;  // You can replace this with any integer value

        // Checking if the number is positive using an 'if' statement
        if (number > 0) {
            // Printing a message if the number is positive
            System.out.println("The entered number is positive.");
        }
        // Checking if the number is negative using another 'if' statement
        if (number < 0) {
            // Printing a message if the number is negative
            System.out.println("The entered number is negative.");
        }
        // Checking if the number is zero using a third 'if' statement
        if (number == 0) {
            // Printing a message if the number is zero
            System.out.println("The entered number is zero.");
        }
    }
}

Output:

The entered number is positive.

2. if-else Statement:

In Java programming, the if-else statement serves as a control flow construct that allows for the efficient implementation of conditional logic. By providing two separate blocks of code to execute based on whether a specified condition is met or not, this statement expands upon the functionality of the traditional if statement. Essentially, it offers a means of handling both true and false outcomes of a condition with ease.

Syntax:

if (condition) {
    //Code to be executed if the condition is true
} else {
    //If the is condition is false the code is being executed
}

Condition: In Java, expressions produce a Boolean outcome, representing either true or false.
If the condition derived from the expression is true, the code enclosed within the first pair of curly brackets is executed.
Conversely, when the condition evaluates to false, the code within the second pair of curly brackets (following the else keyword) is executed.
The conditional structure enables the program to take different actions based on the true or false result of the expression.

Filename: EligibilityChecker.java

public class EligibilityChecker {
    public static void main(String[] args) {
        // For illustration purposes, using a predetermined value instead of user input
        int userAge = 10;  // You can replace this with any integer value

        // Ascertain whether the individual is eligible to vote using an if statement
        if (userAge >= 18) {
            System.out.println("Congratulations! You have attained the eligible voting age.");
        } else {
            System.out.println("Apologies, you are currently not eligible to vote.");
            System.out.println("You will achieve voting eligibility in " + (18 - userAge) + " year(s).");
        }
    }
}

Output:

Apologies, you are currently not eligible to vote.
You will achieve voting eligibility in 8 year(s).

3. Nested if Statement

In Java, a nested if Statement is an if Statement that is inside another if Statement. It means you can have one or more if statements inside another if Statement's block. The inner if statements are executed only if the outer if Statement's condition is true.

Syntax:

if (condition1) {
    //Code to be executed if condition1 is true
    if (condition2) {
        // code to be executed if both condition1 and condition2 are true
    }
    // more Code inside the outer if block
}
//Code outside the outer if block

In this structure, the condition is evaluated first. If it is true, the inner block of the Code is executed. Inside the inner block, condition2 is considered. If it is also true, the Code inside the inner if Statement is executed.

Filename: NestedIfStatementExample.java

public class NestedIfStatementExample {

    public static void main(String[] args) {
        int number = 75;  // You can replace this with any integer value

        // Validate if the number is below 100
        if (number < 100) {
            System.out.println("The given number is less than 100.");

            // Check if the number is evenly divisible by 5
            if (number % 5 == 0) {
                System.out.println("It is a multiple of 5.");
            } else {
                System.out.println("It is not a multiple of 5.");
            }
        } else {
            System.out.println("The given number is greater than or equal to 100.");
        }

        System.out.println("Exiting the nested if-else block."); // Signify the end of the nested if-else block
    }
}

Output:

The given number is less than 100.
It is a multiple of 5.
Exiting the nested if-else block.

4. if- else if- else Statement

In Java, the if-else if-else Statement acts as a decision-making tool, enabling you to execute different code blocks based on various conditions. It's a versatile tool for handling multiple possible outcomes in your program. Think of it as a branching path where you choose the appropriate direction based on specific criteria.

Syntax:

if (condition1) {
    //Code to be executed if condition1 is true
} else if (condition2) {
    //Code to be executed if condition2 is true
} else {
    //Code to be executed if all conditions are false
}

The if Statement checks condition1. If condition1 is true, the corresponding block of Code inside the first set of curly braces is executed.
If condition1 is false, the program evaluates condition2 specified after the else if. If condition2 is true, the corresponding block of Code inside the second set of curly braces is executed.
If both condition1 and condition2 are false, the Code inside the else block is executed.

Filename: GradeCalculator.java

public class GradeCalculator {
    public static void main(String[] args) {
        // For demonstration purposes, using a predefined value instead of user input
        int score = 85;  // You can replace this with any integer value

        char grade; // Declare a variable to store the grade

        // Using if-else if-else Statement to determine the grade based on the score
        if (score >= 90) {
            grade = 'A'; // If score is 90 or above, assign 'A'
        } else if (score >= 80) {
            grade = 'B'; // If score is between 80 and 89, assign 'B'
        } else if (score >= 70) {
            grade = 'C'; // If score is between 70 and 79, assign 'C'
        } else if (score >= 60) {
            grade = 'D'; // If score is between 60 and 69, assign 'D'
        } else {
            grade = 'F'; // If score is below 60, assign 'F'
        }

        System.out.println("The student's exam score is: " + score);
        System.out.println("Based on the score, the student's grade is: " + grade);
    }
}

Output:

The student's exam score is: 85
Based on the score, the student's grade is: B

5. Switch Statement

In Java, the switch statement is a useful tool for controlling the flow of program execution based on a given expression's evaluation. It enables developers to simplify their code by condensing numerous conditional statements into a single statement. The switch statement assesses the value of the specified expression and subsequently matches it against various predefined constants (known as case labels) located inside the switch block. If a matching case is found, the corresponding code is executed.

Syntax:

switch (expression) {
    case value1:
        //Code to be executed if the expression matches the value1
        break;
    case value2:
        //Code to be executed if the expression matches the value2
        break;
    // More cases can follow
    default:
        //Code to be executed if none of the cases match the expression
}

Expression: The switch statement starts by assessing the value of the expression enclosed in parentheses. It then proceeds to match this value against the values specified in the case labels.
case Labels: Each case label represents a possible value that the expression is compared against. If the expression matches a case value, the code block associated with that case label is executed.
break Statement: After executing the code block for a matched case, it's essential to include a break statement to exit the switch statement. Without a break, the execution would continue to the next case, which may not be the desired behaviour.
default Case: The default case is optional. If none of the case values matches the expression, the Code inside the default block is executed. It serves as a catch-all for unhandled cases

Filename: DayOfWeek.java

public class DayOfWeek {
    public static void main(String[] args) {
        // For demonstration purposes, using a predefined value instead of user input
        int dayNumber = 3;  // You can replace this with any integer value

        String dayName; // Declare a variable to store the day name

        // Switch statement to match the input number with corresponding day name
        switch (dayNumber) {
            case 1:
                dayName = "Sunday";
                break;
            case 2:
                dayName = "Monday";
                break;
            case 3:
                dayName = "Tuesday";
                break;
            case 4:
                dayName = "Wednesday";
                break;
            case 5:
                dayName = "Thursday";
                break;
            case 6:
                dayName = "Friday";
                break;
            case 7:
                dayName = "Saturday";
                break;
            default:
                dayName = "Invalid day number"; // If input is not in the range 1-7
                break;
        }
        
        // Output the result
        System.out.println("The entered day number corresponds to: " + dayName);
    }
}

Output:

The entered day number corresponds to: Tuesday

6. Jump

Jump statements in Java are used to alter the normal flow of control in a program. These statements transfer the program's control to another part of the code based on specific conditions or requirements. Java provides three types of jump statements: break, continue, and return.

a. break: In Java, the break statement is used to terminate the loop or switch statement it is within. When a break statement is encountered, the program exits the loop or switch Statement immediately, and the control is transferred to the following Statement after the loop or switch block.

Filename: BreakExample.java

public class BreakExample {
    public static void main(String[] args) {
        // Initialize variables 'start' and 'end'.
        int start = 1;
        int end = 10;

        // Begin a 'for' loop with 'i' starting at 'start', continuing while 'i' is less than or equal to 'end',
        // and incrementing 'i' by 1 in each iteration.
        for (int i = start; i <= end; i++) {
            // Check if the current number 'i' is even.
            if (i % 2 == 0) {
                // Display the first even number encountered within the specified range.
                System.out.println("The first even number found in the range is: " + i);
                // Terminate the loop upon finding the first even number.
                break; // Terminate the loop upon finding the first even number
            }
        }
    }
}

Output:

The first even number found in the range is: 2

b. continue: The continue statement is used to skip the current iteration of a loop and move to the next iteration. It is often used to bypass some specific logic within a loop iteration.

Filename: ContinueExample.java

public class ContinueExample {
    public static void main(String[] args) {
        // Initialize a for loop with 'i' starting at 1 and running while 'i' is less than or equal to 5.
        for (int i = 1; i <= 5; i++) {
            // Check if 'i' is equal to 3.
            if (i == 3) {
                // If 'i' is 3, continue to the next iteration, skipping the rest of the loop code for this value of 'i'.
                continue;
            }
            // Print the current value of 'i' along with a message.
            System.out.println("Current number is: " + i);
        }
    }
}

Output:

Current number is: 1
Current number is: 2
Current number is: 4
Current number is: 5

c. return: The return statement is not limited to selection statements but is used to exit from a method and return a value. It can be used in various conditional and control flow scenarios to exit a method early.

Filename: ReturnExample.java

public class ReturnExample {
    public static void main(String[] args) {
        // Declare a variable 'result' and store the returned value from the 'calculateSum' method with arguments 5 and 10.
        int result = calculateSum(5, 10);
        
        // Print the message "Sum:" along with the value of 'result'.
        System.out.println("Sum: " + result);
    }

    // Define a method 'calculateSum' that takes two integers 'a' and 'b' as parameters.
    public static int calculateSum(int a, int b) {
        // Declare a variable 'sum' and calculate the sum of 'a' and 'b'.
        int sum = a + b;
        
        // Return the calculated sum to the caller.
        return sum; // Returns the sum to the caller
    }
}

Output:

Sum: 15

Conclusion

Selection statements, also known as branching statements or conditional statements or decision-making statements, are vital components in Java programming. They allow developers to control the flow of a program's execution based on specific conditions, making the Code dynamic and responsive. In Java, there are several types of selection statements:

If Statement: Executes code if a specified condition is true.
If-Else Statement: Provides an alternative code block if the initial condition is false.
Nested If Statement: Allows multiple levels of decision-making by placing one if Statement inside another.
If-Else If Statement: Sequentially evaluates multiple conditions, executing the block associated with the first true condition found.
Switch Statement: Compares an expression with case values, executing the corresponding code block when a match is found.
Jump Statements in Java: Controlling Program Flow
Java includes three jump statements:
1. Break: Ends a loop or switch statement.
2. Continue: Skips the rest of the loop and moves to the next iteration.
3. Return: Exits a method, optionally returning a value.