package com.semanticsquare.lambdas;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;
import org.htmlcleaner.HtmlCleaner;
/**
* Demonstrates:
*
* Function & Predicate (including Chaining & Compose)
* Bi-Function as an alternate to Predicate
*
* Consumer & Supplier
* Show API too (including primitive functional interfaces) !!
*
* Method References
* TODO: Constructor References
*
* @author Dheeru Mundluru
*
*/
public class FunctionalInterfaceDemo {
public static void main(String[] args) {
String doc1 = "One of the most common uses of streams is to represent queries over data in collections";
String doc2 = "Information integration systems provide valuable services to users by integrating information from a number of autonomous, heterogeneous and distributed Web sources";
String doc3 = "Solr is the popular, blazing fast open source enterprise search platform from the Apache Lucene";
String doc4 = "Java 8 goes one more step ahead and has developed a streams API which lets us think about parallelism";
List documents = new ArrayList<>(Arrays.asList(doc1, doc2, doc3, doc4));
List targetDocuments = new ArrayList<>();
for (String doc : documents) {
//boolean isTargetDoc = filter(doc, d -> d.contains("stream"));
//BiFunction biFunction = (d, c) -> d.contains(c);
// (iii) Method References (ClassName::instanceMethod)
Function function = doc::contains;
BiFunction biFunction = String::contains;
//if (biFunction.apply(doc, "stream")) {
if (function.apply("stream")) {
//doc = transform(doc, d -> Indexer.stripHtmlTags(d));
//doc = transform(doc, d -> Indexer.removeStopwords(d));
Function htmlCleaner = d -> Indexer.stripHtmlTags(d);
doc = transform(doc, htmlCleaner);
//Function stopwordRemover = d -> Indexer.removeStopwords(d);
//doc = stopwordRemover.apply(doc);
// (i) Method References (ClassName::staticMethod)
Function stopwordRemover = Indexer::removeStopwords;
doc = stopwordRemover.apply(doc);
// Note: Type of Method reference should be appropriate for the abstract method in fn'al interface
// Function docProcessor = htmlCleaner.andThen(stopwordRemover);
// doc = transform(doc, docProcessor);
//System.out.println(doc);
targetDocuments.add(doc);
}
}
//targetDocuments.forEach(d -> System.out.println(d));
// (ii) Method References (objectRef::instanceMethod)
targetDocuments.forEach(System.out::println);
for (String doc : targetDocuments) {
try {
if (doc.length() > 80) {
throw new Exception("Oversized document!!!");
}
} catch (Exception e) {
print(() -> e.getMessage() + " ~ " + doc);
}
}
}
private static boolean errorFlag = true;
private static void print(Supplier supplier) {
if (errorFlag) {
System.out.println(supplier.get());
}
}
static boolean filter(String doc, Predicate filter) {
return filter.test(doc);
}
/*static String transform(String doc, UnaryOperator transformer) {
return transformer.apply(doc);
}*/
static String transform(String doc, Function transformer) {
return transformer.apply(doc);
}
}
class Indexer {
private static List stopWords = Arrays.asList("of", "the", "a", "is", "to", "in", "and");
static String stripHtmlTags(String doc) {
return new HtmlCleaner().clean(doc).getText().toString();
}
static String removeStopwords(String doc) {
StringBuilder sb = new StringBuilder();
for (String word : doc.split(" ")) {
if (!stopWords.contains(word))
sb.append(word).append(" ");
}
return sb.toString();
}
}