Java Reference
In-Depth Information
As the last example in this category, you will use the method reference
Person::getFirstName
that is an instance
method reference on an unbound receiver, as shown:
List<Person> personList = Person.getPersons();
// Maps each Person object to its first name
List<String> firstNameList = FunctionUtil.map(personList,
Person::getFirstName
);
// Prints the first name list
FunctionUtil.forEach(firstNameList,
System.out::println
);
John
Wally
Donna
Supertype Instance Method References
The keyword
super
is used as a qualifier to invoke the overridden method in a class or an interface. The keyword
is available only in an instance context. Use the following syntax to construct a method reference that refers to the
instance method in the supertype and the method that's invoked on the current instance:
TypeName.super::instanceMethod
Consider the
Priced
interface and the
Item
class in Listing 5-15 and Listing 5-16. The
Priced
interface contains a
default method that returns 1.0. The
Item
class implements the
Priced
interface. It overrides the
toString()
method
of the
Object
class and the
getPrice()
method of the
Priced
interface. I have added three constructors to the
Item
class that display a message on the standard output. I will use them in examples in the next section.
Listing 5-15.
A Priced Interface with a Default Method of getPrice()
// Priced.java
package com.jdojo.lambda;
public interface Priced {
default double getPrice() {
return 1.0;
}
}
Listing 5-16.
An Item Class That Implements the Priced Interface
// Item.java
package com.jdojo.lambda;
import java.util.function.Supplier;
public class Item implements Priced {
private String name = "Unknown";
private double price = 0.0;
