Control Statements in Java

Overview

Control statements in Java manage how a program is executed. It is a fundamental concept that any Java programmer must understand. They are one of the first things taught to a beginner joining any Java course.

In this tutorial, we will delve into control statements in Java with examples to better understand the concept.

What Are Control Statements in Java?

Control statements are used in Java to manage a program's execution flow. Based on specific conditions or criteria, they decide which parts of the code should be run and when. Java offers several control statements.

Types of Control Flow Statements

Here are the eight essential types of control statements in Java:

If- else

The if-else control statement allows us to perform different actions based on evaluating a condition. If the condition is true, the code within the if block is executed; otherwise, the code within the else block (if present) is executed. This enables us to control the flow of our program based on specific conditions.

Example:

public class main {
    public static void main(String[] args) {
        int number = 10;


        if (number > 0) {
            System.out.println("The number is positive.");
        } else {
            System.out.println("The number is non-positive.");
        }
    }
}

In this example, we have an int variable called number initialized with a value of 10.

We use the if-else control statement to check whether the number is greater than 0. If the condition (number > 0) evaluates to true, the code within the if block is executed, which in this case prints "The number is positive." to the console.

If the condition evaluates to false, indicating that number is not greater than 0, the code within the else block is executed, which prints "The number is non-positive." to the console.

When you run this program, it will output "The number is positive." since the value of number is indeed greater than 0.

switch

The switch control statement provides a way to execute different blocks of code based on the value of a variable. It offers a cleaner alternative to using multiple if-else statements when comparing against multiple possible values.

Example:

public class main {
    public static void main(String[] args) {
        int day = 3;
        String dayName;

        switch (day) {
            case 1:
                dayName = "Monday";
                break;
            case 2:
                dayName = "Tuesday";
                break;
            case 3:
                dayName = "Wednesday";
                break;
            case 4:
                dayName = "Thursday";
                break;
            case 5:
                dayName = "Friday";
                break;
            case 6:
                dayName = "Saturday";
                break;
            case 7:
                dayName = "Sunday";
                break;
            default:
                dayName = "Invalid day";
                break;
        }

        System.out.println("Day " + day + " is " + dayName + ".");
    }
}

In this example, we have an int variable called day initialized with a value of 3. We also declare a String variable called dayName to store the corresponding name of the day.

We use the switch control statement to match the value of day with different cases. Each case represents a specific value that day could take. When a case matches the value of day, the corresponding block of code is executed.

In this example, when day is 3, the code within the case 3: block is executed, which assigns the value "Wednesday" to dayName. The break; statement is used to exit the switch block once the corresponding case is executed.

If none of the cases match the value of day, the code within the default: block is executed. In this example, if day is any value other than 1-7, the value "Invalid day" is assigned to dayName.

Finally, we print the value of day and dayName using the System.out.println() statement.

When you run this program, it will output "Day 3 is Wednesday.", indicating that the value of day is 3 and the corresponding day name is "Wednesday".

for

The for loop is commonly used when we know the number of iterations in advance or want to iterate over a specific range of values. It provides a concise way to control the iteration process with the initialization, condition, and iteration components all in one line.

Example:

public class main {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++) {
            System.out.println("Count: " + i);
        }
    }
}

This example has a for loop that iterates from 1 to 5. The loop consists of three parts: initialization (int i = 1), condition (i <= 5), and iteration (i++).

Inside the loop, we print the value of i using the System.out.println() statement. The loop will execute five times, printing the value of i from 1 to 5.

while

As long as a particular condition is true, it repeatedly runs a block of code. Each cycle begins with a condition check.

Example:

public class main {
    public static void main(String[] args) {
        int count = 1;

        while (count <= 5) {
            System.out.println("Count: " + count);
            count++;
        }
    }
}

In this example, a while loop executes a block of code repeatedly as long as the condition (count <= 5) evaluates to true. Inside the while loop, we print the value of count and then increment it. The loop will iterate five times, printing the value of count from 1 to 5.

do-while

The condition is verified after the code block has been executed, similar to the "while" statement. As a result, the code block is always run at least once.

Example:

public class main {
    public static void main(String[] args) {
        int count = 1;

        do {
            System.out.println("Count: " + count);
            count++;
        } while (count <= 5);
    }
}

This example has a do-while loop, similar to the while loop. The code block is executed first, then the condition (count <= 5) is checked. If the condition is true, the loop continues to iterate. The loop will execute at least once, regardless of whether the condition is true or false. In this case, it will iterate five times, printing the value of count from 1 to 5.

break

It is used to end the current iteration of a loop or switch statement and the entire loop or switch early.

Example:

public class main {
    public static void main(String[] args) {
        for (int i = 1; i <= 10; i++) {
            if (i == 5) {
                break;
            }
            System.out.println("Value: " + i);
        }
    }
}

This example has a for loop that iterates from 1 to 10. Inside the loop, we check if the value of i equals 5. If the condition is true, the break statement is encountered, and the loop is immediately terminated. As a result, the loop will only execute up to the value of 4, and "Value: 5" will not be printed.

continue

It is employed to go directly to the subsequent iteration of a loop while skipping the current iteration.

Example:

public class main {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++) {
            if (i == 3) {
                continue;
            }
            System.out.println("Value: " + i);
        }
    }
}

This example has a for loop that iterates from 1 to 5. Inside the loop, we check if the value of i is equal to 3. If the condition is true, the continue statement is encountered, and the remaining code in the loop is skipped for that iteration. As a result, when i is 3, the loop continues to the next iteration, and "Value: 3" is not printed. The loop continues for the remaining iterations, printing "Value: 1", "Value: 2", "Value: 4", and "Value: 5".

return

The return statement allows us to terminate the execution of a method and provide a value back to the caller. It is commonly used to return a result or a specific value from a method for further computations or output.

Example:

public class main {
    public static void main(String[] args) {
        int result = sum(5, 7);
        System.out.println("Sum: " + result);
    }


    public static int sum(int a, int b) {
        int sum = a + b;
        return sum;
    }
}

In this example, we have a sum method that takes two integers as parameters (a and b). Inside the method, we calculate the sum of the two numbers and store it in the sum variable.

The return statement is used to return the calculated sum from the method back to the caller. In this case, we return the value of sum.

In the main method, we call the sum method and pass the values 5 and 7 as arguments. The returned value from the sum method is assigned to the result variable.

Finally, we print the value of the result, which will be the sum of 5 and 7, resulting in the output: "Sum: 12".

These control statements offer versatility and let you make programs that can effectively manage various conditions. You may manage the execution flow and strengthen the responsiveness and scalability of your programs by employing the right control statements.

Conclusion

In Java, control statements are crucial for how a program is executed. They let you make choices, repeat code snippets, and change the way statements normally follow one another in order.

Java supports conditional statements like if-else and switch to execute code depending on conditions. You can repeat code blocks using looping statements like for, while, and do-while. The internal flow of loops and switch statements can be managed with jump statements like break and continue. You can develop dynamic, interactive programs that effectively handle various circumstances and conditions using these control statements.

You can check out courses on Java from upGrad to learn more.

FAQs

1. What is the difference between an if-else statement and a switch statement?

You can use the if-else statement to examine a single condition and run various code blocks depending on whether it is true or false. On the other hand, the switch statement enables you to choose which of numerous code blocks to run depending on the result of an expression.

2. When is a while loop preferable to a for loop?

When you need to iterate across a collection or array or when you know the number of iterations in advance, a for loop is typically employed. On the other hand, a while loop is used when a specified condition must be met and the number of iterations is unknown.

3. How does a loop function with the continue statement?

Use the continue command to go to the next iteration of a loop and skip the remaining statements in the current iteration. It enables you to continue executing a loop while avoiding a portion of its code.

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