String in Switch Case in Java

The switch statement is a control structure in Java that provides an efficient way to dispatch execution to different parts of the code based on the value of an expression. In Java, the expression can be a byte, short, char, int, enumerated type, String, or Wrapper class. The ability to use a String-based expression was introduced in JDK 7, and it is a significant improvement over using the equivalent sequence of if/else statements.

When using a String-based switch statement, there are certain key points that must be kept in mind. First, switching on strings can be more expensive in terms of execution than switching on primitive data types. Therefore, it is best to switch on strings only in cases where the controlling data is already in string form. Second, ensure that the expression in any switch statement is not null while working with strings to prevent a NullPointerException from being thrown at run-time. Third, the comparison of String objects in switch statements is case sensitive. Finally, the Java compiler generates generally more efficient bytecode from switch statements that use String objects than from chained if-then-else statements.

Let's look at some examples to understand how to use String-based switch statements in Java. In the first example, we will write a program that demonstrates the use of String to control a switch statement. Here is the code:

java
public class StringSwitchExample {
    public static void main(String[] args) {
        String str = "two";
        switch(str) {
            case "one":
                System.out.println("one");
                break;
            case "two":
                System.out.println("two");
                break;
            case "three":
                System.out.println("three");
                break;
            default:
                System.out.println("no match");
                break;
        }
    }
}

In this example, we have defined a String variable str with a value of "two". We then use a switch statement to determine the corresponding action based on the value of str. The switch statement includes three cases for the values "one", "two", and "three", respectively. If none of these values match, the default case is executed and the output is "no match". When we run this program, the output will be "two".

Now let's look at another example that demonstrates how to handle null strings in a switch statement.

java
public class NullStringSwitchExample {
    public static void main(String[] args) {
        String str = null;
        switch(str) {
            case "one":
                System.out.println("one");
                break;
            case "two":
                System.out.println("two");
                break;
            case "three":
                System.out.println("three");
                break;
            default:
                System.out.println("no match");
                break;
        }
    }
}

In this example, we have defined a String variable str with a null value. When we run this program, we will get a NullPointerException at run-time. To prevent this, we need to ensure that the expression in any switch statement is not null while working with strings.

In conclusion, the switch statement in Java is a powerful control structure that can be used to dispatch execution to different parts of the code based on the value of an expression. When working with String-based switch statements, it is important to remember that switching on strings can be more expensive than switching on primitive data types, to avoid null strings, and to remember that the comparison of String objects in switch statements is case sensitive. With these points in mind, String-based switch statements can be a very effective tool for developers.