From 9038a9a5280a4f098ba60507996b2aeb2d1e6ed1 Mon Sep 17 00:00:00 2001
From: Martin Goik <goik@hdm-stuttgart.de>
Date: Sat, 28 Nov 2015 23:51:30 +0100
Subject: [PATCH] Extended functional programming
---
.../mi/javastreams/CsvCollector.java | 72 ++++++++++++++++
.../hdm_stuttgart/mi/javastreams/Student.java | 31 +++++--
.../mi/javastreams/Java8FunctionalTest.java | 80 +++++++++++++++---
.../mi/javastreams/RosterTest.java | 83 ++++++++++++++-----
.../hdm_stuttgart/mi/javastreams/Student.java | 36 ++++++--
.../mi/javastreams/Java8FunctionalTest.java | 43 ++++++++--
6 files changed, 290 insertions(+), 55 deletions(-)
create mode 100644 P/Sda1/Streams/Solution/src/main/java/de/hdm_stuttgart/mi/javastreams/CsvCollector.java
diff --git a/P/Sda1/Streams/Solution/src/main/java/de/hdm_stuttgart/mi/javastreams/CsvCollector.java b/P/Sda1/Streams/Solution/src/main/java/de/hdm_stuttgart/mi/javastreams/CsvCollector.java
new file mode 100644
index 000000000..252404812
--- /dev/null
+++ b/P/Sda1/Streams/Solution/src/main/java/de/hdm_stuttgart/mi/javastreams/CsvCollector.java
@@ -0,0 +1,72 @@
+package de.hdm_stuttgart.mi.javastreams;
+
+import java.util.EnumSet;
+import java.util.Set;
+import java.util.function.BiConsumer;
+import java.util.function.BinaryOperator;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.stream.Collector;
+
+/**
+ * Turning a list of strings into a character separated list of words. Example:
+ *
+ * List {"Fred", "Eve", "Petra" } and separator "+" results
+ * in the string "Fred+Eve+Petra".
+ *
+ */
+public class CsvCollector implements Collector<String, StringBuffer, String> {
+
+ final String separator;
+
+ /**
+ * Providing the list's desired separator string.
+ * @param separator String filling the gap between two adjacent strings.
+ */
+ public CsvCollector(final String separator) {
+ this.separator = separator;
+ }
+
+ @Override
+ public Supplier<StringBuffer> supplier() {
+ return () -> new StringBuffer();
+ }
+
+ @Override
+ public BiConsumer<StringBuffer, String> accumulator() {
+ return (csv, s) -> {
+ if (0 != csv.length()) { // Buffer non-empty?
+ csv.append(separator); // ==> Append separator ...
+ }
+ csv.append(s); // and string.
+ };
+ }
+
+ @Override
+ public BinaryOperator<StringBuffer> combiner() {
+ return (csv1, csv2) -> {
+ if (0 == csv1.length()) { // Left list empty?
+ return csv2; // ==> return right list.
+
+ } else if (0 == csv2.length()) { // Right List empty?
+ return csv1; // ==> return left list.
+
+ } else { // Both lists non-empty?
+ return csv1. // ==> Concatenate both lists.
+ append(separator).
+ append(csv2);
+ }
+ };
+ }
+
+ @Override
+ public Function<StringBuffer, String> finisher() {
+ return csv -> csv.toString();
+ }
+
+ @Override
+ public Set<java.util.stream.Collector.Characteristics> characteristics() {
+ return EnumSet.of(Characteristics.UNORDERED);
+ }
+
+}
diff --git a/P/Sda1/Streams/Solution/src/main/java/de/hdm_stuttgart/mi/javastreams/Student.java b/P/Sda1/Streams/Solution/src/main/java/de/hdm_stuttgart/mi/javastreams/Student.java
index 8e3a64d9f..0b506d7c8 100644
--- a/P/Sda1/Streams/Solution/src/main/java/de/hdm_stuttgart/mi/javastreams/Student.java
+++ b/P/Sda1/Streams/Solution/src/main/java/de/hdm_stuttgart/mi/javastreams/Student.java
@@ -34,8 +34,10 @@ package de.hdm_stuttgart.mi.javastreams;
import java.util.Arrays;
import java.util.List;
+/** Representing students among with examination marks. */
public class Student {
+ /** @return Test sample of students. */
public static List<Student> createRoster() { // Create test data records
final Student[] roster = new Student[] {
@@ -49,12 +51,18 @@ public class Student {
return Arrays.asList(roster);
}
+ /** Male or female */
public enum Sex {
- MALE("male"), FEMALE("female");
+ /** */
+ MALE("male"),
+ /** */
+ FEMALE("female");
final String extern;
private Sex(final String extern) {this.extern = extern;}
+
+ @Override
public String toString(){return extern;}
}
@@ -71,22 +79,34 @@ public class Student {
this.emailAddress = email;
}
+ /** * @return An examination's result */
public int getMark() {
return mark;
}
- public Sex getGender() {
+
+ /** @return A student's sex. */
+ public Sex getSex() {
return gender;
}
+ /** @return A student's name. */
public String getName() {
return name;
}
+ /** @return A student's e-mail. */
public String getEmailAddress() {
return emailAddress;
}
- public static int compareByMark(Student a, Student b) {
+ /**
+ * Compare two students by their marks
+ * @param a first student
+ * @param b second student
+ * @return positive if student b's mark is better than student a's,
+ * zero if marks are equal, negative if ...
+ */
+ public static int compareByMark(final Student a, final Student b) {
return a.mark - b.mark;
}
@@ -94,9 +114,4 @@ public class Student {
public String toString() {
return getName() + "(" + gender + ", " + getEmailAddress() + ", mark=" + getMark() + ")";
}
-
- public void print() {
- System.out.println(this);
- }
-
}
\ No newline at end of file
diff --git a/P/Sda1/Streams/Solution/src/test/java/de/hdm_stuttgart/mi/javastreams/Java8FunctionalTest.java b/P/Sda1/Streams/Solution/src/test/java/de/hdm_stuttgart/mi/javastreams/Java8FunctionalTest.java
index f6b78ef79..39a44d258 100644
--- a/P/Sda1/Streams/Solution/src/test/java/de/hdm_stuttgart/mi/javastreams/Java8FunctionalTest.java
+++ b/P/Sda1/Streams/Solution/src/test/java/de/hdm_stuttgart/mi/javastreams/Java8FunctionalTest.java
@@ -2,9 +2,11 @@ package de.hdm_stuttgart.mi.javastreams;
import static org.hamcrest.MatcherAssert.assertThat;
+import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.OptionalDouble;
+import java.util.stream.Collector;
import java.util.stream.Collectors;
import org.hamcrest.Matchers;
@@ -40,8 +42,7 @@ public class Java8FunctionalTest {
public void allMaleDistinctNameOrderedByEmail() {
final List<String> emails =
- roster.
- stream().
+ roster.parallelStream().
filter(s -> s.gender == Sex.MALE).
sorted((s1, s2) -> s1.getEmailAddress().compareTo(s2.getEmailAddress())).
map(Student::getName).
@@ -67,13 +68,62 @@ public class Java8FunctionalTest {
public void markSumAllStudentsMarksHavingEmail_Dot_de() {
Assert.assertEquals(
3, //Expected marks sum 3 == 1 + 2
- roster.stream()
+ roster.parallelStream()
.filter(p -> p.emailAddress.endsWith(".de")) // Jane and Kim
.mapToInt(Student::getMark)
.reduce(0, (a, b) -> a + b)
);
}
+ /**
+ * A comma separated string containing all students' alphabetically ordered
+ * email addresses:
+ *
+ * "bob@uk.edu, fred@example.com, george@math.edu, ..."
+ *
+ */
+ @Test
+ public void orderedCharacterSeparatedEmailList() {
+
+ Assert.assertEquals(
+ "bob@uk.edu, fred@example.com, george@math.edu, jane@kiv.de, wilde@serious.de",
+
+ roster.parallelStream().
+ map(Student::getEmailAddress).
+ sorted().
+ collect(new CsvCollector(", ")) // Using ", " as separator string.
+ );
+
+ }
+
+ /**
+ * Achieves the same result as in {@link #orderedCharacterSeparatedEmailList()}
+ * internally using a standard collector with a modified
+ * {@link Collector#finisher()} method:
+ *
+ * "bob@uk.edu, fred@example.com, george@math.edu, ..."
+ *
+ */
+ @Test
+ public void orderedCharacterSeparatedEmailList2() {
+
+ Assert.assertEquals(
+ "bob@uk.edu, fred@example.com, george@math.edu, jane@kiv.de, wilde@serious.de",
+
+ roster.parallelStream().
+ map(Student::getEmailAddress).
+ sorted().
+ collect
+ (Collectors.collectingAndThen
+ (Collectors.toList(),
+ l -> l.stream(). // A stream within a stream.
+ reduce((s1, s2) -> s1 + ", " + s2).
+ get()
+ )
+ )
+ );
+ }
+
/**
* Get the average mark of all female students as double value.
*
@@ -83,7 +133,8 @@ public class Java8FunctionalTest {
@Test
public void averageMarkFemaleStudents() {
- final OptionalDouble femaleAverage = roster.stream().
+ final OptionalDouble femaleAverage =
+ roster.parallelStream().
filter(s -> s.gender == Sex.FEMALE).
mapToInt(Student::getMark).
average();
@@ -111,10 +162,10 @@ public class Java8FunctionalTest {
final Map<Student.Sex, List<String>> studentnamesBySex =
roster
- .stream()
+ .parallelStream()
.collect(
Collectors.groupingBy(
- Student::getGender,
+ Student::getSex,
Collectors.mapping(
Student::getName,
Collectors.toList())
@@ -144,7 +195,7 @@ public class Java8FunctionalTest {
public void markingFrequencies() {
final Map<Integer, Integer> frequencyByMark =
roster
- .stream()
+ .parallelStream()
.collect(
Collectors.groupingBy(
Student::getMark,
@@ -175,17 +226,24 @@ public class Java8FunctionalTest {
*
*/
@Test
- public void studentsByMark() {
+ public void studentnamessByMark() {
+
final Map<Integer, List<String>> namesByMark =
roster
- .stream()
- .sorted((s1,s2) -> s1.name.compareTo(s2.name))
+ .parallelStream()
.collect(
Collectors.groupingBy(
Student::getMark,
Collectors.mapping(
Student::getName,
- Collectors.toList())
+ Collectors.collectingAndThen(
+ Collectors.toList(),
+ l -> {
+ Collections.sort(l);
+ return l;
+ }
+ )
+ )
)
);
diff --git a/P/Sda1/Streams/Template/src/main/java/de/hdm_stuttgart/mi/javastreams/RosterTest.java b/P/Sda1/Streams/Template/src/main/java/de/hdm_stuttgart/mi/javastreams/RosterTest.java
index f1b9293d9..4bee36942 100644
--- a/P/Sda1/Streams/Template/src/main/java/de/hdm_stuttgart/mi/javastreams/RosterTest.java
+++ b/P/Sda1/Streams/Template/src/main/java/de/hdm_stuttgart/mi/javastreams/RosterTest.java
@@ -14,7 +14,7 @@ import java.util.function.Predicate;
*/
public class RosterTest {
- static final List<Student> roster = Student.createRoster();
+ static final List<Student> rosterInstance = Student.createRoster();
interface CheckStudent {
boolean test(Student p);
@@ -23,16 +23,25 @@ public class RosterTest {
// Approach 1: Create Methods that Search for Persons that Match One
// Characteristic
+ /**
+ * @param roster
+ * @param mark
+ */
public static void printPersonsOlderThan(List<Student> roster, int mark) {
for (Student p : roster) {
if (p.getMark()>= mark) {
- p.print();;
+ p.print();
}
}
}
// Approach 2: Create More Generalized Search Methods
+ /**
+ * @param roster
+ * @param low
+ * @param high
+ */
public static void printPersonsWithinMarkRange(
List<Student> roster, int low, int high) {
for (Student p : roster) {
@@ -46,6 +55,10 @@ public class RosterTest {
// Approach 4: Specify Search Criteria Code in an Anonymous Class
// Approach 5: Specify Search Criteria Code with a Lambda Expression
+ /**
+ * @param roster
+ * @param tester
+ */
public static void printPersons(
List<Student> roster, CheckStudent tester) {
for (Student p : roster) {
@@ -57,6 +70,10 @@ public class RosterTest {
// Approach 6: Use Standard Functional Interfaces with Lambda Expressions
+ /**
+ * @param roster
+ * @param tester
+ */
public static void printPersonsWithPredicate(
List<Student> roster, Predicate<Student> tester) {
for (Student p : roster) {
@@ -68,6 +85,11 @@ public class RosterTest {
// Approach 7: Use Lambda Expressions Throughout Your Application
+ /**
+ * @param roster
+ * @param tester
+ * @param block
+ */
public static void processPersons(
List<Student> roster,
Predicate<Student> tester,
@@ -81,6 +103,12 @@ public class RosterTest {
// Approach 7, second example
+ /**
+ * @param roster
+ * @param tester
+ * @param mapper
+ * @param block
+ */
public static void processPersonsWithFunction(
List<Student> roster,
Predicate<Student> tester,
@@ -96,6 +124,12 @@ public class RosterTest {
// Approach 8: Use Generics More Extensively
+ /**
+ * @param source
+ * @param tester
+ * @param mapper
+ * @param block
+ */
public static <X, Y> void processElements(
Iterable<X> source,
Predicate<X> tester,
@@ -109,9 +143,12 @@ public class RosterTest {
}
}
+ /**
+ * @param args unused
+ */
public static void main(String... args) {
- for (Student p : roster) {
+ for (Student p : rosterInstance) {
p.print();
}
@@ -119,13 +156,13 @@ public class RosterTest {
// Characteristic
System.out.println("Persons older than 20:");
- printPersonsOlderThan(roster, 20);
+ printPersonsOlderThan(rosterInstance, 20);
System.out.println();
// Approach 2: Create More Generalized Search Methods
System.out.println("Persons between the ages of 14 and 30:");
- printPersonsWithinMarkRange(roster, 14, 30);
+ printPersonsWithinMarkRange(rosterInstance, 14, 30);
System.out.println();
// Approach 3: Specify Search Criteria Code in a Local Class
@@ -133,15 +170,16 @@ public class RosterTest {
System.out.println("Persons who are eligible for Selective Service:");
class CheckStudentEligibleForSelectiveService implements CheckStudent {
- public boolean test(Student p) {
- return p.getGender() == Student.Sex.MALE
+ @Override
+ public boolean test(Student p) {
+ return p.getSex() == Student.Sex.MALE
&& p.getMark() >= 2
&& p.getMark() <= 3;
}
}
printPersons(
- roster, new CheckStudentEligibleForSelectiveService());
+ rosterInstance, new CheckStudentEligibleForSelectiveService());
System.out.println();
@@ -152,10 +190,11 @@ public class RosterTest {
"(anonymous class):");
printPersons(
- roster,
+ rosterInstance,
new CheckStudent() {
+ @Override
public boolean test(Student p) {
- return p.getGender() == Student.Sex.MALE
+ return p.getSex() == Student.Sex.MALE
&& p.getMark() >= 2
&& p.getMark() <= 3;
}
@@ -170,8 +209,8 @@ public class RosterTest {
"(lambda expression):");
printPersons(
- roster,
- (Student p) -> p.getGender() == Student.Sex.MALE
+ rosterInstance,
+ (Student p) -> p.getSex() == Student.Sex.MALE
&& p.getMark() >= 2
&& p.getMark() <= 3
);
@@ -185,8 +224,8 @@ public class RosterTest {
"(with Predicate parameter):");
printPersonsWithPredicate(
- roster,
- p -> p.getGender() == Student.Sex.MALE
+ rosterInstance,
+ p -> p.getSex() == Student.Sex.MALE
&& p.getMark() >= 18
&& p.getMark() <= 25
);
@@ -199,8 +238,8 @@ public class RosterTest {
"(with Predicate and Consumer parameters):");
processPersons(
- roster,
- p -> p.getGender() == Student.Sex.MALE
+ rosterInstance,
+ p -> p.getSex() == Student.Sex.MALE
&& p.getMark() >= 2
&& p.getMark() <= 3,
p -> p.print()
@@ -214,8 +253,8 @@ public class RosterTest {
"(with Predicate, Function, and Consumer parameters):");
processPersonsWithFunction(
- roster,
- p -> p.getGender() == Student.Sex.MALE
+ rosterInstance,
+ p -> p.getSex() == Student.Sex.MALE
&& p.getMark() >= 2
&& p.getMark() <= 3,
p -> p.getEmailAddress(),
@@ -230,8 +269,8 @@ public class RosterTest {
"(generic version):");
processElements(
- roster,
- p -> p.getGender() == Student.Sex.MALE
+ rosterInstance,
+ p -> p.getSex() == Student.Sex.MALE
&& p.getMark() >= 2
&& p.getMark() <= 3,
p -> p.getEmailAddress(),
@@ -246,10 +285,10 @@ public class RosterTest {
System.out.println("Persons who are eligible for Selective Service " +
"(with bulk data operations):");
- roster
+ rosterInstance
.stream()
.filter(
- p -> p.getGender() == Student.Sex.MALE
+ p -> p.getSex() == Student.Sex.MALE
&& p.getMark() >= 2
&& p.getMark() <= 3)
.map(p -> p.getEmailAddress())
diff --git a/P/Sda1/Streams/Template/src/main/java/de/hdm_stuttgart/mi/javastreams/Student.java b/P/Sda1/Streams/Template/src/main/java/de/hdm_stuttgart/mi/javastreams/Student.java
index 8e3a64d9f..80c48c353 100644
--- a/P/Sda1/Streams/Template/src/main/java/de/hdm_stuttgart/mi/javastreams/Student.java
+++ b/P/Sda1/Streams/Template/src/main/java/de/hdm_stuttgart/mi/javastreams/Student.java
@@ -34,8 +34,10 @@ package de.hdm_stuttgart.mi.javastreams;
import java.util.Arrays;
import java.util.List;
+/** Representing students among with examination marks. */
public class Student {
+ /** @return Test sample of students. */
public static List<Student> createRoster() { // Create test data records
final Student[] roster = new Student[] {
@@ -49,52 +51,72 @@ public class Student {
return Arrays.asList(roster);
}
+ /** Male or female */
public enum Sex {
- MALE("male"), FEMALE("female");
+ /** */
+ MALE("male"),
+ /** */
+ FEMALE("female");
final String extern;
private Sex(final String extern) {this.extern = extern;}
+ @Override
public String toString(){return extern;}
}
String name;
int mark;
- Sex gender;
+ Sex sex;
String emailAddress;
Student(String name, int mark ,
- Sex gender, String email) {
+ Sex sex, String email) {
this.name = name;
this.mark = mark;
- this.gender = gender;
+ this.sex = sex;
this.emailAddress = email;
}
+ /** * @return An examination's result */
public int getMark() {
return mark;
}
- public Sex getGender() {
- return gender;
+
+ /** @return A student's sex. */
+ public Sex getSex() {
+ return sex;
}
+ /** @return A student's name. */
public String getName() {
return name;
}
+ /** @return A student's e-mail. */
public String getEmailAddress() {
return emailAddress;
}
+ /**
+ * Compare two students by their marks
+ * @param a first student
+ * @param b second student
+ * @return positive if student b's mark is better than student a's,
+ * zero if marks are equal, negative if ...
+ */
public static int compareByMark(Student a, Student b) {
return a.mark - b.mark;
}
@Override
public String toString() {
- return getName() + "(" + gender + ", " + getEmailAddress() + ", mark=" + getMark() + ")";
+ return getName() + "(" + sex + ", " + getEmailAddress() + ", mark=" + getMark() + ")";
}
+ /**
+ * Printing all data to standard output.
+ */
public void print() {
System.out.println(this);
}
diff --git a/P/Sda1/Streams/Template/src/test/java/de/hdm_stuttgart/mi/javastreams/Java8FunctionalTest.java b/P/Sda1/Streams/Template/src/test/java/de/hdm_stuttgart/mi/javastreams/Java8FunctionalTest.java
index f82115081..8edfdd587 100644
--- a/P/Sda1/Streams/Template/src/test/java/de/hdm_stuttgart/mi/javastreams/Java8FunctionalTest.java
+++ b/P/Sda1/Streams/Template/src/test/java/de/hdm_stuttgart/mi/javastreams/Java8FunctionalTest.java
@@ -4,6 +4,8 @@ import static org.hamcrest.MatcherAssert.assertThat;
import java.util.List;
import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collector;
import java.util.stream.Collectors;
import org.hamcrest.Matchers;
@@ -33,7 +35,6 @@ public class Java8FunctionalTest {
* "Kim", 2, Student.Sex.FEMALE, "wilde@serious.de"
*
* ==> {"Bob", "Fred", "George"}
- *
*/
@Test
public void allMaleDistinctNameOrderedByEmail() {
@@ -41,9 +42,9 @@ public class Java8FunctionalTest {
final List<String> emails =
roster.
stream().
- filter(s -> s.gender == Sex.MALE).
- sorted((s1, s2) -> s1.getEmailAddress().compareTo(s2.getEmailAddress())).
+ filter(s -> s.sex == Sex.MALE).
map(Student::getName).
+ sorted().
distinct().
collect(Collectors.toList());
@@ -66,20 +67,50 @@ public class Java8FunctionalTest {
* Implementation hint: Map objects to int and provide a suitable reduce operation.
* You may want to read
* https://docs.oracle.com/javase/tutorial/collections/streams/reduction.html#reduce
- *
*/
@Test
public void markSumAllStudentsMarksHavingEmail_Dot_de() {
Assert.fail("Implement me!");// TODO
}
+ /**
+ * A comma separated string containing all students' alphabetically ordered
+ * email addresses:
+ *
+ * "bob@uk.edu, fred@example.com, george@math.edu, ..."
+ *
+ * Hint: Read
+ * http://www.nurkiewicz.com/2014/07/introduction-to-writing-custom.html
+ * and learn how to write custom collectors. Then implement a string collector
+ * which uses a {@link StringBuffer} collecting the string elements. Its
+ * finisher() method may then return the desired result string.
+ */
+ @Test
+ public void orderedCharacterSeparatedEmailList() {
+ Assert.fail("Implement me!");// TODO
+ }
+
+ /**
+ * Achieves the same result as in {@link #orderedCharacterSeparatedEmailList()}
+ * internally using a standard collector with a modified
+ * {@link Collector#finisher()} method:
+ *
+ * "bob@uk.edu, fred@example.com, george@math.edu, ..."
+ *
+ * Hint: Consider {@link Collectors#collectingAndThen(Collector, Function)} and
+ * read http://www.adam-bien.com/roller/abien/entry/java_8_reducing_a_list.
+ */
+ @Test
+ public void orderedCharacterSeparatedEmailList2() {
+ Assert.fail("Implement me!");// TODO
+ }
+
/**
* Get the average mark of all female students as double value.
*
* Implementation hint: Map objects to int and provide a suitable reduce operation.
* You may want to read
* https://docs.oracle.com/javase/8/docs/api/java/util/stream/IntStream.html#average--
- *
*/
@Test
public void averageMarkFemaleStudents() {
@@ -101,7 +132,6 @@ public class Java8FunctionalTest {
*
* Implementation hint:
* stackoverflow.com/questions/2509293/map-equality-using-hamcrest#answer-29680356
- *
*/
@Test
public void studentNamesBySex() {
@@ -141,7 +171,6 @@ public class Java8FunctionalTest {
* Implementation hint: Sort the stream by student's names beforehand. Then
* apply a suitable
* {@link Collectors#mapping(java.util.function.Function, java.util.stream.Collector)}
- *
*/
@Test
public void studentsByMark() {
--
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