Terminal Operations in Java Streams

Hi Everyone reading,

In the previous article, we explored Intermediate Operations in Java Streams — how they transform and prepare data.

Now it’s time to understand the final and most important step of stream processing:

Without a terminal operation, a stream does nothing.

Let’s understand why.

What are Terminal Operations?

Terminal operations:

• Produce a result.
• Trigger execution of intermediate operations.
• Close the stream after execution.
• Cannot be reused once executed.

Example

List<Integer> list = List.of(1,2,3,4,5);

list.stream()
    .filter(n -> n % 2 == 0)
    .forEach(System.out::println);   // Terminal operation

Here:

filter() → Intermediate

forEach() → Terminal (executes the stream)

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Why Terminal Operations Are Important

Streams are lazy.

Intermediate operations build a pipeline, but execution starts only when a terminal operation is called.

No terminal operation → No processing.

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Types of Terminal Operations

Terminal operations can be grouped into:

• Iteration operations
• Reduction operations
• Collection operations
• Matching operations
• Finding operations

Let’s explore each.

1 forEach()

Used to iterate over elements.

List<String> names = List.of("Ram", "Amit", "Shyam");

names.stream()
     .forEach(System.out::println);

Output

Ram
Amit
Shyam

Note: Prefer forEachOrdered() when working with parallel streams and order matters.

2 collect()

Most powerful terminal operation.

Used to collect stream elements into:

• List
• Set
• Map
• String
• Custom collections

Collect to List

List<Integer> evenNumbers = 
    List.of(1,2,3,4,5).stream()
        .filter(n -> n % 2 == 0)
        .collect(Collectors.toList()); // [2,4]

Collect to Map

Map<String, Integer> map =
    List.of("Ram", "Amit", "Shyam").stream()
        .collect(Collectors.toMap(
            name -> name,
            name -> name.length()
        )); // {Ram=3, Amit=4, Shyam=5}

3 reduce()

Used to combine elements into a single result.

Example: Sum of numbers

int sum = List.of(1,2,3,4)
              .stream()
              .reduce(0, (a,b) -> a + b);

System.out.println(sum);

Output

10

Used for:

• Sum
• Product
• Custom aggregation

4 count()

Returns number of elements.

long count = List.of(1,2,3,4,5)
                 .stream()
                 .filter(n -> n > 2)
                 .count();

System.out.println(count);

Output

3

In the above example, we only count the numbers that are greater than 2.

5 anyMatch(), allMatch(), noneMatch()

Used for condition checking.

boolean anyEven =
    List.of(1,3,5,6).stream()
        .anyMatch(n -> n % 2 == 0); // true

boolean allPositive =
    List.of(1,2,3).stream()
        .allMatch(n -> n > 0); // true

boolean result = List.of(5, 10, 15, 20).stream()
                     .noneMatch(n -> n < 0); // true

These return boolean.

6 findFirst() and findAny()

Return an Optional.

Optional<Integer> first =
    List.of(10,20,30)
        .stream()
        .findFirst(); // Optional[10]

findAny() is useful with parallel streams.

Optional<Integer> result =
                List.of(10, 20, 30, 40, 50)
                    .parallelStream()
                    .findAny(); // Optional[30]

Note: In the output of findAny(), there could be any element within the provided list in the output. In this case it was Optional[30], but 30 could be 10,20,40 or 50. findAny() returns any one element in the given list.

7 min() and max()

Find minimum or maximum element.

Optional<Integer> max =
    List.of(1,5,2,9,3)
        .stream()
        .max(Integer::compareTo); // 9

Optional<Integer> min =
    List.of(1,5,2,9,3)
        .stream()
        .min(Integer::compareTo); // 1

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Important Characteristics of Terminal Operations

Feature	Description
Triggers Execution	Executes all intermediate operations
Produces Result	Returns value or side effect
Closes Stream	Stream cannot be reused
Non-lazy	Actually performs computation

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Stream Cannot Be Reused

Stream<Integer> stream = Stream.of(1,2,3);

stream.forEach(System.out::println);

// This will throw IllegalStateException
stream.count();

Once a terminal operation is called, the stream is closed.

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Real-World Example (Employee Processing)

Problem statement: For a given list of employees, find the average salary.

class Employee {
    String name;
    int salary;

    Employee(String name, int salary) {
        this.name = name;
        this.salary = salary;
    }

    public String toString() {
        return name + " : " + salary;
    }
}

public class Main {
    public static void main(String[] args) {

        List<Employee> employees = List.of(
                new Employee("Ram", 50000),
                new Employee("Amit", 70000),
                new Employee("Shyam", 40000),
                new Employee("Ankit", 90000)
        );

        // Get average salary
        double avgSalary = employees.stream()
                .mapToInt(e -> e.salary)
                .average()
                .orElse(0);

        System.out.println("Average Salary: " + avgSalary);
    }
}

Output

Average Salary: 62500.0

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Intermediate vs Terminal Operations

Intermediate	Terminal
Returns Stream	Returns result
Lazy	Executes pipeline
Can chain	Ends stream
filter(), map()	collect(), reduce(), count()

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Conclusion

Terminal operations are the final step in stream processing.

They:

• Execute the pipeline
• Produce meaningful results
• Close the stream

Mastering terminal operations like collect(), reduce(), count(), and findFirst() makes you confident with Java Streams in real-world applications.

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What’s Next?

In the next article, we will explore:
Collectors in depth