Java Streams Terminal Operations Explained with Examples

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In our previous post, we explored intermediate operations in Java Streams. Now, let’s move to terminal operations. These are the final operations that produce a result (like a value, collection, or side-effect) and terminate the stream pipeline.

1. forEach()

The forEach() method is used to perform an action for each element of the stream.

List<String> words = Arrays.asList("apple", "banana", "cherry");
words.forEach(word -> System.out.println("item is " + word));

2. collect()

The collect() method gathers the elements of a stream into a collection (like a List, Set, or Map).

List<Integer> nums = Arrays.asList(1,1,2,2,2,3,4,5,5,5,6);
Set<Integer> res = nums.stream().collect(Collectors.toSet());
System.out.println(res);

3. reduce()

The reduce() method performs a reduction on the elements of the stream using an accumulation function.

List<Integer> nums = Arrays.asList(1,2,3,4,5);
Optional<Integer> res = nums.stream().reduce((a,b) -> a*b);
System.out.println(res.get());

4. allMatch()

Checks if all elements of the stream satisfy a given condition.

List<Integer> nums = Arrays.asList(1,2,3,4,5);
boolean res = nums.stream().allMatch(n -> n > 0);
System.out.println(res);

5. anyMatch()

Checks if any element of the stream satisfies the condition.

List<Integer> nums = Arrays.asList(1,2,3,4,5);
boolean res = nums.stream().anyMatch(n -> n > 4);
System.out.println(res);

6. noneMatch()

Checks if no element in the stream satisfies the condition.

List<Integer> nums = Arrays.asList(1,2,3,4,5);
boolean res = nums.stream().noneMatch(n -> n < 0);
System.out.println(res);

7. findFirst()

Returns the first element of the stream wrapped in an Optional.

List<String> words = Arrays.asList("apple", "banana", "cherry");
Optional<String> res = words.stream().filter(w -> w.startsWith("c")).findFirst();
System.out.println(res.get());

8. findAny()

Returns any one element from the stream (especially useful in parallel streams).

List<String> words = Arrays.asList("apple", "banana", "cherry");
Optional<String> res = words.stream().filter(w -> w.startsWith("c")).findAny();
System.out.println(res.get());

9. max() and min()

Used to find the maximum and minimum elements using a comparator.

List<Integer> nums = Arrays.asList(9,5,2,7,3);
Optional<Integer> max = nums.stream().max((a, b) -> a-b);
Optional<Integer> min = nums.stream().min((a, b) -> a-b);
System.out.println("Max: " + max.get());
System.out.println("Min: " + min.get());

10. toArray()

Converts the stream into an array.

List<String> words = Arrays.asList("apple", "banana", "cherry");
String[] res = words.stream().toArray(String[]::new);
System.out.println(Arrays.toString(res));

11. count()

Counts the number of elements in the stream.

List<Integer> nums = Arrays.asList(1,2,3,4,5);
long count = nums.stream().count();
System.out.println(count);

12. summaryStatistics()

For numerical streams, summaryStatistics() provides count, sum, min, average, and max in one go.

List<Integer> nums = Arrays.asList(1,2,3,4,5);
IntSummaryStatistics stats = nums.stream().mapToInt(Integer::intValue).summaryStatistics();
System.out.println(stats);

Conclusion

Java Stream terminal operations are essential to extract results from a pipeline. From forEach() to summaryStatistics(), these operations help us transform, analyze, and finalize data in a concise way.

By combining intermediate and terminal operations, you can build powerful data-processing pipelines in Java with clean and readable code.

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