Lambda Expressions - Beginning Java 8 Language Features - page 147

Listing 5-13. A FunctionUtil Class
// FunctionUtil.java
package com.jdojo.lambda;
import java.util.ArrayList;
import java.util.List;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
public class FunctionUtil {
// Applies an action on each item in a list
public static <T> void forEach(List<T> list, Consumer<? super T> action) {
for(T item : list) {
action.accept(item);
}
}
// Applies a filter to a list and returned the filtered list items
public static <T> List<T> filter(List<T> list, Predicate<? super T> predicate) {
List<T> filteredList = new ArrayList<>();
for(T item : list) {
if (predicate.test(item)) {
filteredList.add(item);
}
}
return filteredList;
}
// Maps each item in a list to a value
public static <T, R> List<R> map(List<T> list, Function<? super T, R> mapper) {
List<R> mappedList = new ArrayList<>();
for(T item : list) {
mappedList.add(mapper.apply(item));
}
return mappedList;
}
}
You will now use the FunctionUtil class as a library user and use the functional interfaces as target types of
lambda expressions. Listing 5-14 shows how to use the FunctionUtil class.
Listing 5-14. Using Functional Interfaces as Target Types of Lambda Expressions as Library Users
// FunctionUtilTest.java
package com.jdojo.lambda;
import static com.jdojo.lambda.Gender.MALE;
import java.util.List;