What is the role of the “default” keyword in Java?

In Java, the keyword “default” has several different uses:

1. In a switch statement, the default keyword represents the code block that is executed when none of the case conditions are met. It is similar to the else part in an if-else statement.
2. The default keyword in interfaces is used to define default methods. Default methods provide a default implementation within the interface, allowing classes that implement the interface to use this method directly without needing to re-implement it.
3. In an enumeration class, the default keyword is used to define a default enum value. When handling an enum type using a switch statement, if all enum values have been processed but there are still other values to handle, you can use default to handle these unknown enum values.
4. In annotations, the default keyword is used to define the default value of an annotation. When using an annotation, if a value for a certain property is not specified, the default value for that property will be used.

In general, the purpose of the default keyword is to provide a default handling method for situations that are unknown or not matched. It can be used for the default branch of a switch statement, the default method of an interface, the default enum value of an enum class, and the default value of an annotation.