Conditionals Statement

Conditionals in Java: if, else, and switch

Conditionals are used in programming to execute a certain block of code based on whether a condition is true or false. In Java, we use the if else if, else and switch statements to perform conditional logic.

Let’s break down how these control flow structures work:

if Statement

The if statement is used to test a condition and execute a block of code if the condition evaluates to true.

Syntax:
    
    if (condition) {
        // code block executes if the condition is true
    }
Example:
    
    public class IfExample {
        public static void main(String[] args) {
            int number = 10;

            // Check if the number is greater than 0
            if (number > 0) {
                System.out.println("The number is positive.");
            }
        }
    }
Output:
    
    The number is positive.

if-else Statement

The if-else statement allows you to execute one block of code if the condition is true, and another block if it is false.

Syntax:
    
    if (condition) {
        // code block executes if the condition is true
    } else {
        // code block executes if the condition is false
    }
Example:
    
    public class IfElseExample {
        public static void main(String[] args) {
            int number = -5;

            // Check if the number is positive or negative
            if (number > 0) {
                System.out.println("The number is positive.");
            } else {
                System.out.println("The number is negative.");
            }
        }
    }
Output:
    
    The number is negative.

if-else if-else Statement

When you have multiple conditions to check, you can use else if to test additional conditions after the if. If none of the conditions are true, the final else block is executed.

Syntax:
    
    if (condition1) {
        // code block executes if condition1 is true
    } else if (condition2) {
        // code block executes if condition2 is true
    } else {
        // code block executes if none of the above conditions are true
    }
Example:
    
    public class IfElseIfExample {
        public static void main(String[] args) {
            int number = 0;

            // Check if the number is positive, negative, or zero
            if (number > 0) {
                System.out.println("The number is positive.");
            } else if (number < 0) {
                System.out.println("The number is negative.");
            } else {
                System.out.println("The number is zero.");
            }
        }
    }
Output:
    
    The number is zero.

switch Statement

The switch statement is used to execute one out of many possible blocks of code based on a single variable's value. It's often more efficient than using multiple if-else if conditions when checking the value of a single variable.

Syntax:
    
    switch (expression) {
        case value1:
            // code block if expression == value1
            break;
        case value2:
            // code block if expression == value2
            break;
        default:
            // code block if none of the cases match
    }
  • expression The value or variable you're evaluating.
  • case value1 The value you're comparing against. If it matches the expression, the code block under that case is executed.
  • break; This keyword is used to exit the switch block. If omitted, the code will "fall through" to the next case (which is often not desired).
  • default: This is an optional section that is executed if none of the case values match the expression.
Example:
    
    public class SwitchExample {
        public static void main(String[] args) {
            int day = 3;

            // Determine the day of the week based on the value of day
            switch (day) {
                case 1:
                    System.out.println("Monday");
                    break;
                case 2:
                    System.out.println("Tuesday");
                    break;
                case 3:
                    System.out.println("Wednesday");
                    break;
                case 4:
                    System.out.println("Thursday");
                    break;
                case 5:
                    System.out.println("Friday");
                    break;
                case 6:
                    System.out.println("Saturday");
                    break;
                case 7:
                    System.out.println("Sunday");
                    break;
                default:
                    System.out.println("Invalid day number");
            }
        }
    }
Output:
    
    Wednesday
Example: Using switch with String

Java also allows you to use switch with String values (since Java 7), making it useful for scenarios where you need to check multiple string values.

    
    public class SwitchStringExample {
        public static void main(String[] args) {
            String color = "green";

            // Determine the color category
            switch (color) {
                case "red":
                    System.out.println("The color is red.");
                    break;
                case "green":
                    System.out.println("The color is green.");
                    break;
                case "blue":
                    System.out.println("The color is blue.");
                    break;
                default:
                    System.out.println("Unknown color.");
            }
        }
    }
Output:
    
    The color is green.