package mediasystem.media;public class MyBook extends MyMedia {  private String publishDate;  private String bookISBN;  public String getPublishDate(){    return publishDate;  }  public void setPublishDate(String publishDate){    this.publishDate = publishDate;  }  public String getBookISBN(){    return bookISBN;  }  public void setBookISBN(String bookISBN){    this.bookISBN = bookISBN;  }}