Added examples for collectors

Java/Collectors/CollectorsExamples.java

@@ -0,0 +1,94 @@
+import java.util.*;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class CollectorsExamples {
+
+    public static void main(String[] args){
+        System.out.println("*****Examples of different Collectors methods*****");
+
+        System.out.println("Example of Collectors.toList : ");
+        System.out.println(Stream.of(4,3,2,7,1).collect(Collectors.toList()));
+
+        System.out.println("***********************");
+        System.out.println("Example of Collectors.toSet : ");
+        System.out.println(Stream.of(1,7,9,2,3,1).collect(Collectors.toSet()));
+
+        System.out.println("***********************");
+        System.out.println("Example of Collectors.toCollection : ");
+        Stream<Integer> stream = Stream.of(1,7,9,2,3,1);
+
+        Set<Integer> set = stream.collect(Collectors
+                .toCollection(TreeSet::new));
+        System.out.println(set);
+
+        System.out.println("***********************");
+        System.out.println("Example of toMap and toConcurrentMap : ");
+        Stream<String> wordStream = Stream.of("one", "hello", "opera", "hi",
+                "music");
+        HashMap<Character, String> m = wordStream.collect(
+                Collectors.toMap(word -> word.charAt(0),
+                        word -> word,
+                        (word1, word2) -> word1 +","+ word2,
+                        HashMap::new));
+        System.out.println(m);
+
+        System.out.println("***********************");
+        System.out.println("Example of summingInt,summingLong and summingDouble : ");
+        Stream<Integer> intStream = Stream.of(1,2,3,4,5);
+        System.out.println(intStream.collect(Collectors.summingInt(Integer::intValue)));
+
+        System.out.println("***********************");
+        System.out.println("Example of averagingInt,averagingLong and averagingDouble : ");
+        Stream<Integer> intStream1 = Stream.of(5,5,4,6,4);
+        System.out.println(intStream1.collect(Collectors.averagingInt(Integer::intValue)));
+
+        System.out.println("***********************");
+        System.out.println("Example of counting, maxBy, minBy : ");
+        Stream<String> strStream = Stream.of("1","2","3","4","5");
+        System.out.println(strStream.collect(Collectors.counting()));
+
+        Stream<Integer> intStream2 = Stream.of(4,2,6,12,33,44);
+        System.out.println(intStream2.collect(Collectors.maxBy(Comparator.naturalOrder())));
+
+        System.out.println("***********************");
+        System.out.println("Example of groupingBy and partitioningBy : ");
+        Stream<String> strStream2 = Stream.of("one","two","b","d","three");
+        System.out.println(strStream2.collect(Collectors.groupingBy(String::length)));
+
+        Stream<Integer> intStream3 = Stream.of(1, 4, 5, 2, 7);
+        System.out.println(intStream3.collect(Collectors.partitioningBy(e -> e % 2 == 0)));
+
+        System.out.println("***********************");
+        System.out.println("Example of summarizingInt,summarizingDouble and summarizingLong : ");
+        Stream<Integer> intStream4 = Stream.of(5, 4, 3, 2, 1);
+        Map<Integer, IntSummaryStatistics> map = intStream4.collect(Collectors.groupingBy(Integer::intValue, Collectors.summarizingInt(Integer::intValue)));
+
+        System.out.println(map);
+
+        System.out.println("***********************");
+        System.out.println("Example of joining : ");
+        Stream<String> strStream3 = Stream.of("one","two","three","four","five");
+        System.out.println(strStream3.collect(Collectors.joining()));
+
+        Stream<String> strStream4 = Stream.of("one","two","three","four","five");
+        System.out.println(strStream4.collect(Collectors.joining("-")));
+
+        Stream<String> strStream5 = Stream.of("one","two","three","four","five");
+        System.out.println(strStream5.collect(Collectors.joining("-","start:",":end")));
+
+        System.out.println("***********************");
+        System.out.println("Example of mapping,flatMapping and reducing : ");
+        Stream<String> strStream6 = Stream.of("one","two","three","four");
+        System.out.println(strStream6.collect(Collectors.groupingBy(String::length,Collectors.mapping(String::toUpperCase,Collectors.toSet()))));
+
+        Stream<String> strStream7 = Stream.of("one","two","three","four");
+        System.out.println(strStream7.collect(Collectors.reducing((str1,str2) -> str1 + str2)).orElse("-"));
+
+        System.out.println("***********************");
+        System.out.println("Example of collectingAndThen : ");
+        Stream<String> strStream8 = Stream.of("sunday","monday","tuesday","wednesday");
+        List<String> strList = strStream8.collect(Collectors.collectingAndThen(Collectors.toList(),Collections::unmodifiableList));
+        System.out.println(strList);
+    }
+}

Java/Collectors/CustomCollector.java

@@ -0,0 +1,61 @@
+import java.util.*;
+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;
+import java.util.stream.Stream;
+
+import static java.util.stream.Collector.Characteristics.IDENTITY_FINISH;
+
+class Student {
+    int marks;
+
+    Student() {
+    }
+
+    public Student(int i) {
+        this.marks = i;
+    }
+
+    Student addMarks(Student s) {
+        return new Student(this.marks = this.marks + s.marks);
+    }
+
+}
+
+class StudentCollector implements Collector<Student, Student, Student> {
+    @Override
+    public Supplier<Student> supplier() {
+        return Student::new;
+    }
+
+    @Override
+    public BiConsumer<Student, Student> accumulator() {
+        return Student::addMarks;
+    }
+
+    @Override
+    public BinaryOperator<Student> combiner() {
+        return Student::addMarks;
+    }
+
+    @Override
+    public Function<Student, Student> finisher() {
+        return Function.identity();
+    }
+
+    @Override
+    public Set<Characteristics> characteristics() {
+        return EnumSet.of(IDENTITY_FINISH);
+    }
+}
+
+
+class CustomCollector {
+    public static void main(String[] args) {
+        Stream<Student> studentStream = Stream.of(new Student(30), new Student(40), new Student(50), new Student(80));
+        System.out.println(studentStream.collect(new StudentCollector()).marks);
+
+    }
+}