Errata

The definition of the static private class
static private class CustomerAsCustomer implements Function1<Customer, Customer> {
public String call(Customer customer) { return customer; }
}

should must likely be
static private class CustomerAsCustomer implements Function1<Customer, String> {
public String call(Customer customer) { return customer; }
}

Otherwise the return type of the method call would be wrong!

static private class CustomerAsCustomer implements Function1<Customer, Customer> {
public String call(Customer customer) { return customer; }
}

on the bottom of page 15 should, as said in the text above the code, a customer object: - not a string
static private class CustomerAsCustomer implements Function1<Customer, Customer> {
public Customer call(Customer customer) { return customer; }
}

In the text at the top the following method is defined (Ex 2-13):
public static List<String> getEnabledCustomerAddresses() {
return Customer.getEnabledCustomerField(new Function1<Customer,String>() {
public String call(Customer customer) { return customer.address; }
});
}

later in Ex 2-14
public static List<String> getEnabledCustomerAddresses() {
return Customer.getEnabledCustomerField(new Function1<Customer,String>() {
public String call(Customer customer) { return customer.addresses; }
});
}
However, the field addresses is undefined.
Probably it should be address, as above.

Code 3-29

public Customer setCustomerId(Integer customer_id) {
this.customer_id = customer_id;
return this;
}

customer_id is not a customer field
id is the customer id.
Probably the code should read
public Customer setCustomerId(Integer customer_id) {
this.id = customer_id;
return this;
}

after (p 50 at the bottom)
public final Boolean enabled = true;

we cannot set enabled as in the code on p 51 (top)
public Contract(Calendar begin_date, Boolean enabled) {
this.begin_date = begin_date;
this.end_date = this.begin_date.getInstance();
this.end_date.setTimeInMillis(this.begin_date.getTimeInMillis());
this.end_date.add(Calendar.YEAR, 2);
this.enabled = enabled;
}
If we want to be able to set the field, then it cannot be final AND initialized.
Probably the code (on P 50) should be
public final Boolean enabled;;
Then the value can be initialized (exactly once).

On page 80 the followinf field are declared and initialized (final)

public final Integer contact_id = 0;
public final String firstName = "";
public final String lastName = "";
public final String email = "";
public final Boolean enabled = true;

on the following constructor (p 80 bottom)
public Contact(Integer contact_id,
String firstName,
String lastName,
String email,
Boolean enabled) {
this.contact_id = contact_id;
this.firstName = firstName;
this.lastName = lastName;
this.email = email;
this.enabled = enabled;
}
the final AND initialized filed are overwritten, which is not possible.
Probably the filed should not be initialized in their declaration (p 80)

public final Integer contact_id;
public final String firstName;
public final String lastName;
public final String email;
public final Boolean enabled;

or the final attribute has to be removed.

public void sendEmail() {
println("Sending Email")
}

should probably be
public void sendEmail() {
System.out. println("Sending Email")
}

public class None<T> implements Option<T> {
public T getOrElse(T defObj) {
return obj;
}

should be without the get...
public class None<T> implements Option<T> {
public T getOrElse(T obj) {
return obj;
}
(as on line 10:
"a getOrElse(T obj) method on the Option interface...")

In functional programming, it is common to make a distinction between "statements" and "expressions". The usual convention is that an expressions (like functions) can be evaluated to a value, while a statement e.g. println("Foo").

In a FP language like Scala, an "if" expression is evaluated to a value, as in the examples in this book, while apparent statements things like println() are actually expressions that return Unit.

A Java "if" statement has no value unless one is explicitly returned, and println() does not return anything.

This book (which is otherwise excellent) seems to get this the wrong way around throughout Chapter 7 e.g. on p. 151 the section header is "Everything Is a Statement", but in fact in functional programming "everything is an expression".