Journal for Developers

Java 8 Streams Terminal Operation

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In the previous journal entry “Understanding Java 8 Streams with Examples” we have looked at the core concepts of Java 8 Streams API with some examples. Then we took a look at the Intermediate operation methods of Java 8 Streams. Now, in this journal we will take a look at some more examples of Java 8 Stream operations: Terminal.

A terminal operation should always be the last operation in a Stream pipeline.

Terminal operations are executed eagerly i.e they process all the elements in the stream before returning the result.

Java 8 Streams Terminal Operation Examples

Let’s have a look at some of the basic use cases of terminal operation methods provided by Stream API.

  1. forEach()
  2. toArray()
  3. reduce()
  4. collect()
  5. count()
  6. max()
  7. min()
  8. anyMatch()
  9. allMatch()
  10. noneMatch()
  11. findFirst()
  12. findAny()

forEach(): Perform an action for each element in the stream. It is basically a simplified inline way for writing a for loop.

Java Stream forEach() Example:
Stream<String> names = Stream.of("Kirsten", "John", "Philips");
names.forEach(name -> System.out.println(name));

toArray(): As shown in the example of the journal “Understanding Java 8 Stream“, it is used to create an Array from a Stream.

Java 8 Stream toArray() Example:
Stream<Integer> intStream = Stream.of(1,2,3,4);
Integer[] intArray = intStream.toArray(Integer[]::new);
System.out.println(Arrays.toString(intArray));
 
//prints [1, 2, 3, 4]

reduce(): A reduction operation (also called a fold) takes a sequence of input elements and combines them into a single summary result.

Java 8 Stream reduce() Example:
Stream<Integer> intStream = Stream.of(1,2,3,4);
int sum = intStream.reduce(0, (x,y) -> x+y);

// OR

int sum = intStream.reduce(0, Integer::sum);

collect(): As shown in the example of the journal “Understanding Java 8 Stream“, we can use java Stream collect() method to accumulate elements in a stream into a container such as a collection.

Java 8 Stream collect() Example:
Stream<Integer> intStream = Stream.of(1,2,3,4);
List<Integer> intList = intStream.collect(Collectors.toList());
System.out.println(intList);
 
//prints [1, 2, 3, 4]
 
//stream is closed, so we need to create it again
intStream = Stream.of(1,2,3,4);
Map<Integer,Integer> intMap = intStream.collect(Collectors.toMap(i -> i, i -> i+10));
System.out.println(intMap);
 
//prints {1=11, 2=12, 3=13, 4=14}

count(): Returns the count of the total number of items availabe in the Stream.

Java 8 Stream count() Example:
Stream<Integer> intStream = Stream.of(1,2,3,4);

System.out.println("Total Number of Elements: " + intStream.count());

// OUTPUT
4

max(): A special reduction operation that returns an Optional describing the maximum element of the stream according to the provided Comparator.

Java 8 Stream max() Example:
public class Person {
    String name;
    int age;

    //Constructors and Getters/Setters are omitted...
}

public class Java8StreamMax {
     
    public static void main(String[] args) {
        List<Person> personList = Arrays.asList(
            new Person("Smith", 37),
            new Person("John", 24),
            new Person("Kirsten", 33)
        );

        //Find Oldest Person
    	final Comparator<Person> comp = (p1, p2) -> Integer.compare( p1.getAge(), p2.getAge());
 
        Person result = personList.stream()	// Convert to steam
                .max(comp)			// Find the Max using the Comparator
                .get();
 
        System.out.println(result);
    }
 
}

min(): A special reduction operation that returns an Optional describing the minimum element of this stream according to the provided Comparator.

Java 8 Stream min() Example:

Taking the same example as above for finding the max(), we will simply replace the method name max() with min().

.
.
.
Person result = personList.stream()	// Convert to steam
                .min(comp)		// Find the Min using the Comparator
                .get();
.
.
.

anyMatch(): Method to find out whether at least one of the elements in the stream matches a given predicate.

Java 8 Stream anyMatch() Example:

Stream<String> names = Stream.of("Kirsten", "John", "Philips");

boolean moreThan6Chars = names.anyMatch(s -> s.length() > 6);

System.out.println("Are names with more than 6 Characters? " + moreThan6Chars);

// OUTPUT
Are names with more than 6 Characters? true

allMatch(): Method to find out whether all the elements in the stream matches a given predicate.

Java 8 Stream allMatch() Example:

Using the same example as above, we can find out whether the length of the names are equal to or more than 4 characters.

.
.
.
boolean equalToMoreThan4Chars = names.allMatch(s -> s.length() >= 4);
.
.
.

noneMatch(): Method to find out that no elements in the stream match a given predicate.

Java 8 Stream noneMatch() Example:

Again using the same example as above, we can find out the names length should not be less than 4 characters.

.
.
.
boolean noLessThan4Chars = namesNoneMatch.noneMatch(s -> s.length() < 4);
.
.
.

findFirst(): Method to find the first element in the stream.

Java 8 Stream findFirst() Example:
Stream<String> names = Stream.of("Kirsten", "John", "Philips");

Optional<String> name = names.filter(i -> i.startsWith("J")).findFirst();

if(name.isPresent()) {
	System.out.println("First Name starting with J = " + name.get());
}

// OUTPUT
John

findAny(): Method to fetch any element of the stream satisfying a given criteria.

Java 8 Stream findAny() Example:
Stream<String> names = Stream.of("Kirsten", "John", "Philips", "Kentucky");

Optional<String> name = names.filter(i -> i.startsWith("K")).findAny();

if ( name.isPresent() ) {
	System.out.println("findAny Name Starting with K: " + name.get());
}

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