Command Design Pattern

In the command pattern, all requests for an object are passed to a common command interface. Each implementing  class of the command interface executes a particular method of the passed-in object when called.

//The command interface (interface or abstract class)
public interface Command {
      public void execute();
}

//The object to be requested for
public BookProcessor {
      String name;

      public BookProcessor(String n) {
            name = n;
      }

      public void borrowBook() {
            System.out.println("Borrowing book: " + name);
      }

      public void returnBook() {
            System.out.println("Returning book: " + name);
     }
}

//The concrete command classes
public class BorrowBook implements Command {
      private BookProcessor bp;

      public BorrowBook(String name) {
            bp = new BookProcessor(name)
      }

      //the command method
      public void execute() {
            bp.borrowBook();
      }
}

public class ReturnBook implements Command {
      private BookProcessor bp;

      public ReturnBook(String name) {
            bp = new BookProcessor(name)
      }

      //the command method
      public void execute() {
            bp.returnBook();
      }
}

//The Runner
public class CommandDemo {
      public static void main(String[] args) {
            Command borrow = new BorrowBook("Readers are Lucky");
            borrow.execute();

            Command return = new ReturnBook("Happy to finish");
            return.execute();
      }
}

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