Java8 stream (#3585)

* java 8 stream code so far

* more examples

* code change

* fix test names

* fix unit test

* move code to correct location

* more unit tests

* more tests

guest/core-java/pom.xml

@@ -16,6 +16,24 @@
 			<artifactId>log4j-core</artifactId>
 			<version>${log4j2.version}</version>
 		</dependency>
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest-core</artifactId>
+            <version>${org.hamcrest.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest-library</artifactId>
+            <version>${org.hamcrest.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest-all</artifactId>
+            <version>${org.hamcrest.version}</version>
+            <scope>test</scope>
+        </dependency>
 	</dependencies>
 
 	<build>
@@ -32,5 +50,6 @@
 	</build>
 	<properties>
 		<log4j2.version>2.8.2</log4j2.version>
+		<org.hamcrest.version>1.3</org.hamcrest.version>
 	</properties>
 </project>

guest/core-java/src/main/java/com/stackify/stream/Employee.java

@@ -0,0 +1,46 @@
+package com.stackify.stream;
+
+public class Employee {
+    private Integer id;
+    private String name;
+    private Double salary;
+    
+    public Employee(Integer id, String name, Double salary) {
+        this.id = id;
+        this.name = name;        
+        this.salary = salary;
+    }
+
+    public Integer getId() {
+        return id;
+    }
+
+    public void setId(Integer id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+    
+    public Double getSalary() {
+        return salary;
+    }
+
+    public void setSalary(Double salary) {
+        this.salary = salary;
+    }
+    
+    public void salaryIncrement(Double percentage) {
+        Double newSalary = salary + percentage * salary / 100;
+        setSalary(newSalary);
+    }
+
+    public String toString() {
+        return "Id: " + id + " Name:" + name + " Price:" + salary;
+    }
+}

guest/core-java/src/main/java/com/stackify/stream/EmployeeRepository.java

@@ -0,0 +1,21 @@
+package com.stackify.stream;
+
+import java.util.List;
+
+public class EmployeeRepository {
+    private List<Employee> empList;
+    
+    public EmployeeRepository(List<Employee> empList) {
+        this.empList = empList;
+    
+    }
+    public Employee findById(Integer id) {
+        for (Employee emp : empList) {
+            if (emp.getId() == id) {
+                return emp;
+            }
+        }
+        
+        return null;
+    }
+}

guest/core-java/src/test/java/com/stackify/stream/EmployeeTest.java

@@ -0,0 +1,455 @@
+package com.stackify.stream;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.beans.HasPropertyWithValue.hasProperty;
+import static org.junit.Assert.assertEquals;
+
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Comparator;
+import java.util.DoubleSummaryStatistics;
+import java.util.List;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Optional;
+import java.util.Set;
+import java.util.Vector;
+import java.util.function.BinaryOperator;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import org.junit.After;
+import org.junit.Test;
+
+public class EmployeeTest {
+    private String fileName = "src/test/resources/test.txt";
+    
+    private static Employee[] arrayOfEmps = {
+        new Employee(1, "Jeff Bezos", 100000.0), 
+        new Employee(2, "Bill Gates", 200000.0), 
+        new Employee(3, "Mark Zuckerberg", 300000.0)
+    };
+
+    private static List<Employee> empList = Arrays.asList(arrayOfEmps);
+    private static EmployeeRepository employeeRepository = new EmployeeRepository(empList);
+
+    @After
+    public void cleanup() throws IOException {
+        Files.deleteIfExists(Paths.get(fileName));
+    }
+    
+    @Test
+    public void whenGetStreamFromList_ObtainStream() {
+        assert(empList.stream() instanceof Stream<?>);
+    }
+
+    @Test
+    public void whenGetStreamFromArray_ObtainStream() {
+        assert(Stream.of(arrayOfEmps) instanceof Stream<?>);
+    }
+
+    @Test
+    public void whenGetStreamFromElements_ObtainStream() {
+        assert(Stream.of(arrayOfEmps[0], arrayOfEmps[1], arrayOfEmps[2]) instanceof Stream<?>);
+    }
+
+    @Test
+    public void whenBuildStreamFromElements_ObtainStream() {
+        Stream.Builder<Employee> empStreamBuilder = Stream.builder();
+        
+        empStreamBuilder.accept(arrayOfEmps[0]);
+        empStreamBuilder.accept(arrayOfEmps[1]);
+        empStreamBuilder.accept(arrayOfEmps[2]);
+
+        Stream<Employee> empStream = empStreamBuilder.build();
+        
+        assert(empStream instanceof Stream<?>);
+    }
+
+    @Test
+    public void whenIncrementSalaryForEachEmployee_thenApplyNewSalary() {
+        Employee[] arrayOfEmps = {
+            new Employee(1, "Jeff Bezos", 100000.0), 
+            new Employee(2, "Bill Gates", 200000.0), 
+            new Employee(3, "Mark Zuckerberg", 300000.0)
+        };
+
+        List<Employee> empList = Arrays.asList(arrayOfEmps);
+        
+        empList.stream().forEach(e -> e.salaryIncrement(10.0));
+        
+        assertThat(empList, contains(
+          hasProperty("salary", equalTo(110000.0)),
+          hasProperty("salary", equalTo(220000.0)),
+          hasProperty("salary", equalTo(330000.0))
+        ));
+    }
+
+    @Test
+    public void whenIncrementSalaryUsingPeek_thenApplyNewSalary() {
+        Employee[] arrayOfEmps = {
+            new Employee(1, "Jeff Bezos", 100000.0), 
+            new Employee(2, "Bill Gates", 200000.0), 
+            new Employee(3, "Mark Zuckerberg", 300000.0)
+        };
+
+        List<Employee> empList = Arrays.asList(arrayOfEmps);
+        
+        empList.stream()
+          .peek(e -> e.salaryIncrement(10.0))
+          .peek(System.out::println)
+          .collect(Collectors.toList());
+
+        assertThat(empList, contains(
+          hasProperty("salary", equalTo(110000.0)),
+          hasProperty("salary", equalTo(220000.0)),
+          hasProperty("salary", equalTo(330000.0))
+        ));
+    }
+
+    @Test
+    public void whenMapIdToEmployees_thenGetEmployeeStream() {
+        Integer[] empIds = { 1, 2, 3 };
+        
+        List<Employee> employees = Stream.of(empIds)
+          .map(employeeRepository::findById)
+          .collect(Collectors.toList());
+        
+        assertEquals(employees.size(), empIds.length);
+    }
+
+    @Test
+    public void whenFlatMapEmployeeNames_thenGetNameStream() {
+        List<List<String>> namesNested = Arrays.asList( 
+          Arrays.asList("Jeff", "Bezos"), 
+          Arrays.asList("Bill", "Gates"), 
+          Arrays.asList("Mark", "Zuckerberg"));
+
+        List<String> namesFlatStream = namesNested.stream()
+          .flatMap(Collection::stream)
+          .collect(Collectors.toList());
+
+        assertEquals(namesFlatStream.size(), namesNested.size() * 2);
+    }
+
+    @Test
+    public void whenFilterEmployees_thenGetFilteredStream() {
+        Integer[] empIds = { 1, 2, 3, 4 };
+        
+        List<Employee> employees = Stream.of(empIds)
+          .map(employeeRepository::findById)
+          .filter(e -> e != null)
+          .filter(e -> e.getSalary() > 200000)
+          .collect(Collectors.toList());
+        
+        assertEquals(Arrays.asList(arrayOfEmps[2]), employees);
+    }
+
+    @Test
+    public void whenFindFirst_thenGetFirstEmployeeInStream() {
+        Integer[] empIds = { 1, 2, 3, 4 };
+        
+        Employee employee = Stream.of(empIds)
+          .map(employeeRepository::findById)
+          .filter(e -> e != null)
+          .filter(e -> e.getSalary() > 100000)
+          .findFirst()
+          .orElse(null);
+        
+        assertEquals(employee.getSalary(), new Double(200000));
+    }
+
+    @Test
+    public void whenCollectStreamToList_thenGetList() {
+        List<Employee> employees = empList.stream().collect(Collectors.toList());
+        
+        assertEquals(empList, employees);
+    }
+
+    @Test
+    public void whenStreamToArray_thenGetArray() {
+        Employee[] employees = empList.stream().toArray(Employee[]::new);
+
+        assertThat(empList.toArray(), equalTo(employees));
+    }
+    
+    @Test
+    public void whenStreamCount_thenGetElementCount() {
+        Long empCount = empList.stream()
+          .filter(e -> e.getSalary() > 200000)
+          .count();
+
+        assertEquals(empCount, new Long(1));
+    }
+
+    @Test
+    public void whenLimitInfiniteStream_thenGetFiniteElements() {
+        Stream<Integer> infiniteStream = Stream.iterate(2, i -> i * 2);
+    
+        List<Integer> collect = infiniteStream
+          .skip(3)
+          .limit(5)
+          .collect(Collectors.toList());
+  
+        assertEquals(collect, Arrays.asList(16, 32, 64, 128, 256));
+    }
+    
+    @Test
+    public void whenSortStream_thenGetSortedStream() {
+        List<Employee> employees = empList.stream()
+          .sorted((e1, e2) -> e1.getName().compareTo(e2.getName()))
+          .collect(Collectors.toList());
+
+        assertEquals(employees.get(0).getName(), "Bill Gates");
+        assertEquals(employees.get(1).getName(), "Jeff Bezos");
+        assertEquals(employees.get(2).getName(), "Mark Zuckerberg");
+    }
+
+
+    @Test
+    public void whenFindMin_thenGetMinElementFromStream() {
+        Employee firstEmp = empList.stream()
+          .min((e1, e2) -> e1.getId() - e2.getId())
+          .orElseThrow(NoSuchElementException::new);
+
+        assertEquals(firstEmp.getId(), new Integer(1));
+    }
+    
+    @Test
+    public void whenFindMax_thenGetMaxElementFromStream() {
+        Employee maxSalEmp = empList.stream()
+          .max(Comparator.comparing(Employee::getSalary))
+          .orElseThrow(NoSuchElementException::new);
+
+        assertEquals(maxSalEmp.getSalary(), new Double(300000.0));
+    }
+    
+    @Test
+    public void whenApplyDistinct_thenRemoveDuplicatesFromStream() {
+        List<Integer> intList = Arrays.asList(2, 5, 3, 2, 4, 3);
+        List<Integer> distinctIntList = intList.stream().distinct().collect(Collectors.toList());
+        
+        assertEquals(distinctIntList, Arrays.asList(2, 5, 3, 4));
+    }
+
+    @Test
+    public void whenApplyMatch_thenReturnBoolean() {
+        List<Integer> intList = Arrays.asList(2, 4, 5, 6, 8);
+        
+        boolean allEven = intList.stream().allMatch(i -> i % 2 == 0);
+        boolean oneEven = intList.stream().anyMatch(i -> i % 2 == 0);
+        boolean noneMultipleOfThree = intList.stream().noneMatch(i -> i % 3 == 0);
+        
+        assertEquals(allEven, false);
+        assertEquals(oneEven, true);
+        assertEquals(noneMultipleOfThree, false);
+    }
+    
+    @Test
+    public void whenFindMaxOnIntStream_thenGetMaxInteger() {
+        Integer latestEmpId = empList.stream()
+          .mapToInt(Employee::getId)
+          .max()
+          .orElseThrow(NoSuchElementException::new);
+
+        assertEquals(latestEmpId, new Integer(3));
+    }
+
+    @Test
+    public void whenApplySumOnIntStream_thenGetSum() {
+        Double avgSal = empList.stream()
+          .mapToDouble(Employee::getSalary)
+          .average()
+          .orElseThrow(NoSuchElementException::new);
+        
+        assertEquals(avgSal, new Double(200000));
+    }
+    
+    @Test
+    public void whenApplyReduceOnStream_thenGetValue() {
+        Double sumSal = empList.stream()
+          .map(Employee::getSalary)
+          .reduce(0.0, Double::sum);
+
+        assertEquals(sumSal, new Double(600000));
+    }
+    
+    @Test
+    public void whenCollectByJoining_thenGetJoinedString() {
+        String empNames = empList.stream()
+          .map(Employee::getName)
+          .collect(Collectors.joining(", "))
+          .toString();
+        
+        assertEquals(empNames, "Jeff Bezos, Bill Gates, Mark Zuckerberg");
+    }
+    
+    @Test
+    public void whenCollectBySet_thenGetSet() {
+        Set<String> empNames = empList.stream()
+                .map(Employee::getName)
+                .collect(Collectors.toSet());
+        
+        assertEquals(empNames.size(), 3);
+    }
+    
+    @Test
+    public void whenToVectorCollection_thenGetVector() {
+        Vector<String> empNames = empList.stream()
+                .map(Employee::getName)
+                .collect(Collectors.toCollection(Vector::new));
+        
+        assertEquals(empNames.size(), 3);
+    }
+
+    @Test
+    public void whenApplySummarizing_thenGetBasicStats() {
+        DoubleSummaryStatistics stats = empList.stream()
+          .collect(Collectors.summarizingDouble(Employee::getSalary));
+
+        assertEquals(stats.getCount(), 3);
+        assertEquals(stats.getSum(), 600000.0, 0);
+        assertEquals(stats.getMin(), 100000.0, 0);
+        assertEquals(stats.getMax(), 300000.0, 0);
+        assertEquals(stats.getAverage(), 200000.0, 0);
+    }
+
+    @Test
+    public void whenApplySummaryStatistics_thenGetBasicStats() {
+        DoubleSummaryStatistics stats = empList.stream()
+          .mapToDouble(Employee::getSalary)
+          .summaryStatistics();
+
+        assertEquals(stats.getCount(), 3);
+        assertEquals(stats.getSum(), 600000.0, 0);
+        assertEquals(stats.getMin(), 100000.0, 0);
+        assertEquals(stats.getMax(), 300000.0, 0);
+        assertEquals(stats.getAverage(), 200000.0, 0);
+    }
+
+    @Test
+    public void whenStreamPartition_thenGetMap() {
+        List<Integer> intList = Arrays.asList(2, 4, 5, 6, 8);
+        Map<Boolean, List<Integer>> isEven = intList.stream().collect(
+          Collectors.partitioningBy(i -> i % 2 == 0));
+        
+        assertEquals(isEven.get(true).size(), 4);
+        assertEquals(isEven.get(false).size(), 1);
+    }
+    
+    @Test
+    public void whenStreamGroupingBy_thenGetMap() {
+        Map<Character, List<Employee>> groupByAlphabet = empList.stream().collect(
+          Collectors.groupingBy(e -> new Character(e.getName().charAt(0))));
+
+        assertEquals(groupByAlphabet.get('B').get(0).getName(), "Bill Gates");
+        assertEquals(groupByAlphabet.get('J').get(0).getName(), "Jeff Bezos");
+        assertEquals(groupByAlphabet.get('M').get(0).getName(), "Mark Zuckerberg");
+    }
+    
+    @Test
+    public void whenStreamMapping_thenGetMap() {
+        Map<Character, List<Integer>> idGroupedByAlphabet = empList.stream().collect(
+          Collectors.groupingBy(e -> new Character(e.getName().charAt(0)),
+            Collectors.mapping(Employee::getId, Collectors.toList())));
+
+        assertEquals(idGroupedByAlphabet.get('B').get(0), new Integer(2));
+        assertEquals(idGroupedByAlphabet.get('J').get(0), new Integer(1));
+        assertEquals(idGroupedByAlphabet.get('M').get(0), new Integer(3));
+    }
+
+    @Test
+    public void whenStreamReducing_thenGetValue() {
+        Double percentage = 10.0;
+        Double salIncrOverhead = empList.stream().collect(Collectors.reducing(
+            0.0, e -> e.getSalary() * percentage / 100, (s1, s2) -> s1 + s2));
+
+        assertEquals(salIncrOverhead, 60000.0, 0);
+    }
+    
+    @Test
+    public void whenStreamGroupingAndReducing_thenGetMap() {
+        Comparator<Employee> byNameLength = Comparator.comparing(Employee::getName);
+        
+        Map<Character, Optional<Employee>> longestNameByAlphabet = empList.stream().collect(
+          Collectors.groupingBy(e -> new Character(e.getName().charAt(0)),
+            Collectors.reducing(BinaryOperator.maxBy(byNameLength))));
+
+        assertEquals(longestNameByAlphabet.get('B').get().getName(), "Bill Gates");
+        assertEquals(longestNameByAlphabet.get('J').get().getName(), "Jeff Bezos");
+        assertEquals(longestNameByAlphabet.get('M').get().getName(), "Mark Zuckerberg");
+    }
+
+    @Test
+    public void whenParallelStream_thenPerformOperationsInParallel() {
+        Employee[] arrayOfEmps = {
+          new Employee(1, "Jeff Bezos", 100000.0), 
+          new Employee(2, "Bill Gates", 200000.0), 
+          new Employee(3, "Mark Zuckerberg", 300000.0)
+        };
+
+        List<Employee> empList = Arrays.asList(arrayOfEmps);
+        
+        empList.stream().parallel().forEach(e -> e.salaryIncrement(10.0));
+        
+        assertThat(empList, contains(
+          hasProperty("salary", equalTo(110000.0)),
+          hasProperty("salary", equalTo(220000.0)),
+          hasProperty("salary", equalTo(330000.0))
+        ));
+    }
+
+    @Test
+    public void whenGenerateStream_thenGetInfiniteStream() {
+        Stream.generate(Math::random)
+          .limit(5)
+          .forEach(System.out::println);
+    }
+
+    @Test
+    public void whenIterateStream_thenGetInfiniteStream() {
+        Stream<Integer> evenNumStream = Stream.iterate(2, i -> i * 2);
+    
+        List<Integer> collect = evenNumStream
+          .limit(5)
+          .collect(Collectors.toList());
+  
+        assertEquals(collect, Arrays.asList(2, 4, 8, 16, 32));
+    }
+
+    @Test
+    public void whenStreamToFile_thenGetFile() throws IOException {
+        String[] words = {
+          "hello", 
+          "refer",
+          "world",
+          "level"
+        };
+        
+        try (PrintWriter pw = new PrintWriter(
+          Files.newBufferedWriter(Paths.get(fileName)))) {
+            Stream.of(words).forEach(pw::println);
+        }
+    }
+    
+    private List<String> getPalindrome(Stream<String> stream, int length) {
+        return stream.filter(s -> s.length() == length)
+          .filter(s -> s.compareToIgnoreCase(
+            new StringBuilder(s).reverse().toString()) == 0)
+          .collect(Collectors.toList());
+    }
+    
+    @Test
+    public void whenFileToStream_thenGetStream() throws IOException {
+        whenStreamToFile_thenGetFile();
+        
+        List<String> str = getPalindrome(Files.lines(Paths.get(fileName)), 5);        
+        assertThat(str, contains("refer", "level"));
+    }
+}