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Can we define a class inside a Java interface?
Yes, you can define a class inside an interface. In general, if the methods of the interface use this class and if we are not using it anywhere else we will declare a class within an interface.
Example
interface Library {
void issueBook(Book b);
void retrieveBook(Book b);
public class Book {
int bookId;
String bookName;
int issueDate;
int returnDate;
}
}
public class Sample implements Library {
public void issueBook(Book b) {
System.out.println("Book Issued");
}
public void retrieveBook(Book b) {
System.out.println("Book Retrieved");
}
public static void main(String args[]) {
Sample obj = new Sample();
obj.issueBook(new Library.Book());
obj.retrieveBook(new Library.Book());
}
}Output
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If we need to provide a default implementation of the interface, we will define a class inside an interface as:
Example
interface Library {
void issueBook(Book b);
void retrieveBook(Book b);
public class Book implements Library {
int bookId;
String bookName;
int issueDate;
int returnDate;
public void issueBook(Book b) {
System.out.println("book issued");
}
public void retrieveBook(Book b) {
System.out.println("book retrieved");
}
}
}
public class Sample {
public void demo() {
System.out.println("Hello welcome to tutorialspoint");
}
public static void main(String args[]) {
Sample obj = new Sample();
obj.demo();
}
}
Updated on: 20-Feb-2020
5K+ Views
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