In Java, the switch statement provides an efficient way to execute different parts of code based on the value of a single variable. Instead of writing multiple if-else statements, we use switch to simplify control flow when dealing with numerous conditions.

What is a switch Statement?

The switch statement evaluates a variable (integer, string, etc.) and executes one of many possible code blocks based on its value. Each possible value is defined by a case label, and once a match is found, the corresponding block of code is executed.

Syntax:

switch (expression) {
    case value1:
        // Code to execute if expression matches value1
        break;
    case value2:
        // Code to execute if expression matches value2
        break;
    // More cases
    default:
        // Code to execute if no cases match
}

• The break statement ensures the program exits the switch block after executing the matching case.
• The default block is optional and runs if no cases match the value of the expression.

Example:

int day = 3;
switch (day) {
    case 1:
        System.out.println("Monday");
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    case 3:
        System.out.println("Wednesday");
        break;
    default:
        System.out.println("Invalid day");
}

Here, day = 3, so the program prints “Wednesday.” If none of the cases match the expression, the default block will execute.

switch with String and Other Data Types

In Java, starting from version 7, we can use the switch statement with strings. This allows more flexibility beyond just numeric values.

Example:

String fruit = "apple";
switch (fruit) {
    case "apple":
        System.out.println("Apples are red.");
        break;
    case "banana":
        System.out.println("Bananas are yellow.");
        break;
    default:
        System.out.println("Unknown fruit.");
}

Here, the variable fruit is evaluated, and based on the value, the corresponding case executes.

switch vs. if-else

Both switch and if-else are conditional statements, but they have different use cases:

• Use switch when evaluating a single variable against multiple fixed values.
• Use if-else for complex conditions or when working with ranges of values.

For instance, in the following case, if-else would be a better option:

int number = 25;
if (number > 0 && number < 50) {
    System.out.println("Number is between 1 and 50.");
} else if (number >= 50 && number < 100) {
    System.out.println("Number is between 50 and 100.");
}

The switch statement is not ideal for range checks but is perfect when testing for equality with specific values.

Advanced Usage: Nested switch

A switch statement can be nested inside another switch to handle more complex cases, but this should be used cautiously as it can make the code harder to follow.

Example:

int age = 20;
String gender = "male";

switch (gender) {
    case "male":
        switch (age) {
            case 20:
                System.out.println("Male and 20 years old.");
                break;
        }
        break;
}

The Role of break

Without the break statement, Java will execute all subsequent cases once a match is found. This is called “fall-through behavior.”

Example (without break):

int number = 2;
switch (number) {
    case 1:
        System.out.println("One");
    case 2:
        System.out.println("Two");
    case 3:
        System.out.println("Three");
}

In this case, the program will print “Two” and “Three” because the break is missing. To avoid this, always include break after each case, unless fall-through is intentional.

Switch Expressions in Java 12+

Starting from Java 12, switch expressions are introduced. They make it possible to return a value from a switch statement, leading to more concise code.

Example:

String day = "Monday";
String message = switch (day) {
    case "Monday", "Tuesday" -> "Start of the week";
    case "Friday" -> "End of the work week";
    default -> "Midweek day";
};
System.out.println(message);

This new format removes the need for break and simplifies the syntax.

Conclusion

The switch statement is a powerful alternative to if-else, especially when handling multiple possible values for a single expression. With the introduction of string support and switch expressions in Java 12, switch has become even more versatile and concise. For more detailed information, we can explore Oracle’s official Java documentation.