关于java中类定义的问题。

最近在学习java，想请教各位大侠，为什么下面代码中构造函数中的形参都是final类型的，这样写有什么好处？
public class Book implements Serializable {
private static final long serialVersionUID = 1L;
private static final int NAME_LENGTH = 100;

private Long bookId;
private String bookName;
private String publisher;

public Book() {
super();
}

public Book(final Long bookId) {
this.bookId = bookId;
}

public Book(final String bookName) {
this.bookName = bookName;
}

public Book(final Long bookId, final String bookName) {
super();
this.bookId = bookId;
this.bookName = bookName;
}