streams

concept/core/src/com/core/stream/a_little_example/Sample.java

@@ -0,0 +1,16 @@
+package com.core.stream.a_little_example;
+
+import java.util.*;
+
+public class Sample {  
+  public static void main(String[] args) {
+    List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+
+    //Print the double of event numbers
+
+    numbers.stream()
+      .filter(e -> e % 2 == 0)
+      .map(e -> e * 2)
+      .forEach(System.out::println);
+  }
+}

concept/core/src/com/core/stream/b_gone_wrong/Sample.java

@@ -0,0 +1,21 @@
+package com.core.stream.b_gone_wrong;
+
+import java.util.*;
+
+public class Sample {  
+  public static void main(String[] args) {
+    List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+
+    //Create a list of double of even numbers
+
+    List<Integer> doubleOfEven = new ArrayList<>();
+
+    numbers.stream()
+      .filter(e -> e % 2 == 0)
+      .map(e -> e * 2)
+      .forEach(e -> doubleOfEven.add(e)); //Don't do this. Shared mutabilty is evil.
+      //This code can't ever be paralleized (well it will misbehave if we do).
+
+    System.out.println(doubleOfEven);
+  }
+}

concept/core/src/com/core/stream/c_the_right_way/Sample.java

@@ -0,0 +1,21 @@
+package com.core.stream.c_the_right_way;
+
+import java.util.*;
+import static java.util.stream.Collectors.*;
+
+public class Sample {  
+  public static void main(String[] args) {
+    List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+
+    //Create a list of double of even numbers
+
+    //The right way, delegate, be declarative, leave it to the APIs
+
+    List<Integer> doubleOfEven = numbers.stream()
+      .filter(e -> e % 2 == 0)
+      .map(e -> e * 2)
+      .collect(toList());
+
+    System.out.println(doubleOfEven);
+  }
+}

concept/core/src/com/core/stream/d_toset/Sample.java

@@ -0,0 +1,21 @@
+package com.core.stream.d_toset;
+
+import java.util.*;
+import static java.util.stream.Collectors.*;
+
+public class Sample {  
+  public static void main(String[] args) {
+    List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+
+    //Create a list of double of even numbers
+
+    //The right way, delegate, be declarative, leave it to the APIs
+
+    Set<Integer> doubleOfEven = numbers.stream()
+      .filter(e -> e % 2 == 0)
+      .map(e -> e * 2)
+      .collect(toSet());
+
+    System.out.println(doubleOfEven);
+  }
+}

concept/core/src/com/core/stream/e_to_unmodifiable/Sample.java

@@ -0,0 +1,19 @@
+package com.core.stream.e_to_unmodifiable;
+
+import java.util.*;
+import static java.util.stream.Collectors.*;
+
+public class Sample {  
+  public static void main(String[] args) {
+    List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+
+    //Create a list of double of even numbers
+
+    List<Integer> doubleOfEven = numbers.stream()
+      .filter(e -> e % 2 == 0)
+      .map(e -> e * 2)
+      .collect(toUnmodifiableList());
+
+    System.out.println(doubleOfEven);
+  }
+}

concept/core/src/com/core/stream/f_partition/Sample.java

@@ -0,0 +1,13 @@
+package com.core.stream.f_partition;
+
+import java.util.*;
+import static java.util.stream.Collectors.*;
+
+public class Sample {  
+  public static void main(String[] args) {
+    List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+
+    System.out.println(numbers.stream()
+      .collect(partitioningBy(e -> e % 2 == 0)));
+  }
+}

concept/core/src/com/core/stream/g_joining/Person.java

@@ -0,0 +1,24 @@
+package com.core.stream.g_joining;
+
+public class Person {
+  private final String name;
+  private final int age;
+
+  public Person(String theName, int theAge) {
+    name = theName;
+    age = theAge;
+  }
+
+  public String getName() { 
+    return name; 
+  }
+
+  public int getAge() { 
+    return age; 
+  }
+
+  public String toString() {
+    return String.format("%s -- %d", name, age);
+  }  
+}
+

concept/core/src/com/core/stream/g_joining/Sample.java

@@ -0,0 +1,29 @@
+package com.core.stream.g_joining;
+
+import java.util.*;
+import static java.util.stream.Collectors.*;
+
+public class Sample {  
+  public static List<Person> createPeople() {
+    return List.of(
+	    new Person("Sara", 20),
+	    new Person("Sara", 22),
+	    new Person("Bob", 20),
+	    new Person("Paula", 32),
+	    new Person("Paul", 32),
+	    new Person("Jack", 2),
+	    new Person("Jack", 72),
+	    new Person("Jill", 12)
+	  );
+  }
+
+  public static void main(String[] args) {
+    List<Person> people = createPeople();
+
+    System.out.println(
+      people.stream()
+        .map(Person::getName)
+        .map(String::toUpperCase)
+        .collect(joining(", ")));
+  }
+}

concept/core/src/com/core/stream/h_grouping/Person.java

@@ -0,0 +1,24 @@
+package com.core.stream.h_grouping;
+
+public class Person {
+  private final String name;
+  private final int age;
+
+  public Person(String theName, int theAge) {
+    name = theName;
+    age = theAge;
+  }
+
+  public String getName() { 
+    return name; 
+  }
+
+  public int getAge() { 
+    return age; 
+  }
+
+  public String toString() {
+    return String.format("%s -- %d", name, age);
+  }  
+}
+

concept/core/src/com/core/stream/h_grouping/Sample.java

@@ -0,0 +1,29 @@
+package com.core.stream.h_grouping;
+
+import java.util.*;
+import static java.util.stream.Collectors.*;
+
+public class Sample {  
+  public static List<Person> createPeople() {
+    return List.of(
+	    new Person("Sara", 20),
+	    new Person("Sara", 22),
+	    new Person("Bob", 20),
+	    new Person("Paula", 32),
+	    new Person("Paul", 32),
+	    new Person("Jack", 2),
+	    new Person("Jack", 72),
+	    new Person("Jill", 12)
+	  );
+  }
+
+  public static void main(String[] args) {
+    List<Person> people = createPeople();
+
+    Map<String, List<Person>> byName =
+      people.stream()
+        .collect(groupingBy(person -> person.getName()));
+
+    System.out.println(byName);
+  }
+}

concept/core/src/com/core/stream/i_and_mapping/Person.java

@@ -0,0 +1,24 @@
+package com.core.stream.i_and_mapping;
+
+public class Person {
+  private final String name;
+  private final int age;
+
+  public Person(String theName, int theAge) {
+    name = theName;
+    age = theAge;
+  }
+
+  public String getName() { 
+    return name; 
+  }
+
+  public int getAge() { 
+    return age; 
+  }
+
+  public String toString() {
+    return String.format("%s -- %d", name, age);
+  }  
+}
+

concept/core/src/com/core/stream/i_and_mapping/Sample.java

@@ -0,0 +1,29 @@
+package com.core.stream.i_and_mapping;
+
+import java.util.*;
+import static java.util.stream.Collectors.*;
+
+public class Sample {  
+  public static List<Person> createPeople() {
+    return List.of(
+	    new Person("Sara", 20),
+	    new Person("Sara", 22),
+	    new Person("Bob", 20),
+	    new Person("Paula", 32),
+	    new Person("Paul", 32),
+	    new Person("Jack", 2),
+	    new Person("Jack", 72),
+	    new Person("Jill", 12)
+	  );
+  }
+
+  public static void main(String[] args) {
+    List<Person> people = createPeople();
+
+    Map<String, List<Integer>> byName =
+      people.stream()
+        .collect(groupingBy(Person::getName, mapping(Person::getAge, toList())));
+
+    System.out.println(byName);
+  }
+}

concept/core/src/com/core/stream/j_collectingandthen/Person.java

@@ -0,0 +1,24 @@
+package com.core.stream.j_collectingandthen;
+
+public class Person {
+  private final String name;
+  private final int age;
+
+  public Person(String theName, int theAge) {
+    name = theName;
+    age = theAge;
+  }
+
+  public String getName() { 
+    return name; 
+  }
+
+  public int getAge() { 
+    return age; 
+  }
+
+  public String toString() {
+    return String.format("%s -- %d", name, age);
+  }  
+}
+

concept/core/src/com/core/stream/j_collectingandthen/Sample.java

@@ -0,0 +1,29 @@
+package com.core.stream.j_collectingandthen;
+
+import java.util.*;
+import static java.util.stream.Collectors.*;
+
+public class Sample {  
+  public static List<Person> createPeople() {
+    return List.of(
+	    new Person("Sara", 20),
+	    new Person("Sara", 22),
+	    new Person("Bob", 20),
+	    new Person("Paula", 32),
+	    new Person("Paul", 32),
+	    new Person("Jack", 2),
+	    new Person("Jack", 72),
+	    new Person("Jill", 12)
+	  );
+  }
+
+  public static void main(String[] args) {
+    List<Person> people = createPeople();
+
+    Map<String, Integer> byName =
+      people.stream()
+        .collect(groupingBy(Person::getName, collectingAndThen(counting(), Long::intValue)));
+
+    System.out.println(byName);
+  }
+}