examples

Author: amigoscode

pom.xml

@@ -7,6 +7,18 @@
     <groupId>com.amigoscode</groupId>
     <artifactId>streams</artifactId>
     <version>1.0-SNAPSHOT</version>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>16</source>
+                    <target>16</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
 
     <properties>
         <maven.compiler.source>17</maven.compiler.source>

src/test/java/com/amigoscode/examples/DistinctAndSets.java

@@ -4,18 +4,26 @@
 import org.junit.jupiter.api.Test;
 
 import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import static org.assertj.core.api.Assertions.assertThat;
 
 public class DistinctAndSets {
 
     @Test
     public void distinct() throws Exception {
         List<Integer> numbers = List.of(1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 9, 9, 9);
-
+        List<Integer> distinct = numbers.stream().distinct().collect(Collectors.toList());
+        assertThat(distinct).hasSize(9);
+        System.out.println(distinct);
     }
 
     @Test
     public void distinctWithSet() throws Exception {
         List<Integer> numbers = List.of(1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 9, 9, 9);
-
+        Set<Integer> distinct = numbers.stream().collect(Collectors.toSet());
+        assertThat(distinct).hasSize(9);
+        System.out.println(distinct);
     }
 }

src/test/java/com/amigoscode/examples/Filtering.java

@@ -5,33 +5,86 @@
 import com.amigoscode.mockdata.MockData;
 import org.junit.jupiter.api.Test;
 
+import java.util.Arrays;
 import java.util.List;
+import java.util.OptionalInt;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 public class Filtering {
 
     @Test
     public void filter() throws Exception {
         List<Car> cars = MockData.getCars();
+
+        Predicate<Car> carPredicate = car -> car.getPrice() < 20_000.00;
+        Predicate<Car> yellow = car -> car.getColor().equals("Yellow");
+
+        List<Car> carsLessThan20k = cars.stream()
+                .filter(carPredicate)
+                .filter(yellow)
+                .collect(Collectors.toList());
+
+        carsLessThan20k.forEach(System.out::println);
     }
 
     @Test
     public void dropWhile() throws Exception {
-        List<Car> cars = MockData.getCars();
+        System.out.println("using filter");
+        Stream.of(2, 4, 6, 8, 9, 10, 12).filter(n -> n % 2 == 0)
+                .forEach(n -> System.out.print(n + " "));
+        System.out.println();
+        System.out.println("using dropWhile");
+        Stream.of(2, 4, 6, 8, 9, 10, 12).dropWhile(n -> n % 2 == 0)
+                .forEach(n -> System.out.print(n + " "));
+
     }
 
     @Test
     public void takeWhile() throws Exception {
-        List<Car> cars = MockData.getCars();
+        // using filter
+        System.out.println("using filter");
+        Stream.of(2, 4, 6, 8, 9, 10, 12).filter(n -> n % 2 == 0)
+                .forEach(n -> System.out.print(n + " "));
+
+        System.out.println();
+        System.out.println("using take while");
+        Stream.of(2, 4, 6, 8, 9, 10, 12).takeWhile(n -> n % 2 == 0)
+                .forEach(n -> System.out.print(n + " "));
     }
 
     @Test
     public void findFirst() throws Exception {
-        Integer[] numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+        int[] numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+        int result = Arrays.stream(numbers).filter(n -> n == 50)
+                .findFirst()
+                .orElse(-1);
+        System.out.println(result);
+
     }
 
     @Test
     public void findAny() throws Exception {
-        Integer[] numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+        int[] numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 9, 10};
+        int result = Arrays.stream(numbers).filter(n -> n == 9)
+                .findAny()
+                .orElse(-1);
+        System.out.println(result);
+    }
+
+    @Test
+    public void allMatch() throws Exception {
+        int[] even = {2, 4, 6, 8, 10};
+        boolean allMatch = Arrays.stream(even).allMatch(n -> n % 2 == 0);
+        System.out.println(allMatch);
+    }
+
+    @Test
+    public void anyMatch() throws Exception {
+        int[] evenAndOneOdd = {2, 4, 6, 8, 10, 11};
+        boolean anyMatch = Arrays.stream(evenAndOneOdd).anyMatch(n -> !(n % 2 == 0));
+        System.out.println(anyMatch);
     }
 
 }

src/test/java/com/amigoscode/examples/GettingStarted.java

@@ -5,7 +5,9 @@
 import org.junit.jupiter.api.Test;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.List;
+import java.util.stream.Collectors;
 
 
 public class GettingStarted {
@@ -15,11 +17,29 @@ public void imperativeApproach() throws IOException {
         // 1. Find people aged less or equal 18
         // 2. Then change implementation to find first 10 people
         List<Person> people = MockData.getPeople();
+        List<Person> youngPeople = new ArrayList<>();
+        int limit = 10;
+        int counter = 0;
+        for (Person person : people) {
+            if (person.getAge() <= 18) {
+                youngPeople.add(person);
+                counter++;
+                if (counter == limit) {
+                    break;
+                }
+            }
+        }
+        youngPeople.forEach(System.out::println);
 
     }
 
     @Test
     public void declarativeApproachUsingStreams() throws Exception {
         List<Person> people = MockData.getPeople();
+        List<Person> youngPeople = people.stream()
+                .filter(p -> p.getAge() <= 18)
+                .limit(10)
+                .collect(Collectors.toList());
+        youngPeople.forEach(System.out::println);
     }
 }

src/test/java/com/amigoscode/examples/GroupingData.java

@@ -1,31 +1,52 @@
 package com.amigoscode.examples;
 
 
+import com.amigoscode.beans.Car;
+import com.amigoscode.mockdata.MockData;
 import org.junit.jupiter.api.Test;
 
 import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collectors;
 
 public class GroupingData {
 
     @Test
     public void simpleGrouping() throws Exception {
+        Map<String, List<Car>> map = MockData.getCars()
+                .stream()
+                .collect(Collectors.groupingBy(Car::getMake));
+        map.forEach((s, cars) -> {
+            System.out.println("Make " + s);
+            cars.forEach(System.out::println);
+            System.out.println("---------------------");
+        });
 
     }
 
     @Test
     public void groupingAndCounting() throws Exception {
         List<String> names = List.of(
-                        "John",
-                        "John",
-                        "Mariam",
-                        "Alex",
-                        "Mohammado",
-                        "Mohammado",
-                        "Vincent",
-                        "Alex",
-                        "Alex"
+                "John",
+                "John",
+                "Mariam",
+                "Alex",
+                "Mohammado",
+                "Mohammado",
+                "Vincent",
+                "Alex",
+                "Alex"
+        );
+
+        Map<String, Long> map = names.stream()
+                .collect(Collectors.groupingBy(
+                        Function.identity(),
+                        Collectors.counting())
                 );
 
+        System.out.println(map);
+
     }
 
 }

src/test/java/com/amigoscode/examples/IntStreams.java

@@ -6,22 +6,38 @@
 import org.junit.jupiter.api.Test;
 
 import java.util.List;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
 
 public class IntStreams {
 
     @Test
     public void range() throws Exception {
-
+        System.out.println("with fori");
+        for (int i = 0; i <= 10; i++) {
+            System.out.println(i);
+        }
+        System.out.println("with int stream exclusive");
+        IntStream.range(0, 10).forEach(System.out::println);
+
+        System.out.println("with int stream inclusive");
+        IntStream.rangeClosed(0, 10).forEach(System.out::println);
     }
 
     // Loop through people using IntStream
     @Test
     public void rangeIteratingLists() throws Exception {
         List<Person> people = MockData.getPeople();
+        IntStream.range(0, people.size())
+                .forEach(index -> {
+                    System.out.println(people.get(index));
+                });
     }
 
     @Test
     public void intStreamIterate()  {
-
+        IntStream.iterate(0, value -> value + 1)
+                .limit(11)
+                .forEach(System.out::println);
     }
 }

src/test/java/com/amigoscode/examples/JoiningStrings.java

@@ -3,17 +3,35 @@
 import org.junit.jupiter.api.Test;
 
 import java.util.List;
+import java.util.stream.Collectors;
 
 public class JoiningStrings {
 
     @Test
-    public void joiningStringsWithStream() throws Exception {
+    public void joiningStrings() throws Exception {
         List<String> names = List.of("anna", "john", "marcos", "helena", "yasmin");
+        // "Anna, John, Marcos, Helena, Yasmin"
+        StringBuilder join = new StringBuilder();
+
+        for (String name : names) {
+            join.append(name.substring(0, 1).toUpperCase())
+                    .append(name.substring(1))
+                    .append(", ");
+        }
+
+        System.out.println(join);
+        System.out.println(join.substring(0, join.length() - 2));
     }
 
     @Test
-    public void joiningStrings() throws Exception {
+    public void joiningStringsWithStream() throws Exception {
         List<String> names = List.of("anna", "john", "marcos", "helena", "yasmin");
+        // "Anna, John, Marcos, Helena, Yasmin"
+        String join = names.stream()
+                .map(name -> name.substring(0, 1).toUpperCase() + name.substring(1))
+                .collect(Collectors.joining("|"));
+        System.out.println(join);
+
     }
 
 }

src/test/java/com/amigoscode/examples/MinMax.java

@@ -2,17 +2,22 @@
 
 import org.junit.jupiter.api.Test;
 
+import java.util.Comparator;
 import java.util.List;
 
 public class MinMax {
 
     @Test
     public void min() {
         List<Integer> numbers = List.of(1, 2, 3, 100, 23, 93, 99);
+        Integer min = numbers.stream().min(Comparator.naturalOrder()).get();
+        System.out.println(min);
     }
 
     @Test
     public void max() {
         List<Integer> numbers = List.of(1, 2, 3, 100, 23, 93, 99);
+        Integer max = numbers.stream().max(Comparator.naturalOrder()).get();
+        System.out.println(max);
     }
 }