Interview question

What is the difference between intermediate and terminal operations in Java Streams? Java Streams में intermediate और terminal operations में क्या अंतर है?

Answer

Type	Returns	Execution	Examples
Intermediate	Another Stream	Lazy - not executed until a terminal op is called	filter, map, sorted, distinct, limit
Terminal	A non-stream result or void	Eager - triggers the whole pipeline to run	collect, forEach, reduce, count, anyMatch

import java.util.stream.*;

List<Integer> numbers = List.of(5, 3, 8, 1, 9, 2);

// Chaining multiple intermediate operations - nothing executes yet
Stream<Integer> pipeline = numbers.stream()
    .filter(n -> n > 2)     // intermediate
    .map(n -> n * 2)         // intermediate
    .sorted();                // intermediate

System.out.println('Pipeline built, nothing executed yet');

// Only when a TERMINAL operation is called does the pipeline actually run
List<Integer> result = pipeline.collect(Collectors.toList());  // terminal - triggers execution
System.out.println(result);  // [6, 10, 16, 18]

// A stream can only have ONE terminal operation - after that it's consumed
// pipeline.count();  // IllegalStateException - stream already consumed

// Short-circuiting operations - some terminals stop early once satisfied
boolean hasLarge = numbers.stream()
    .peek(n -> System.out.println('Checking: ' + n))
    .anyMatch(n -> n > 8);
// Stops as SOON as it finds a match - doesn't process every remaining element

// limit() - an intermediate operation that's also short-circuiting
List<Integer> firstThree = numbers.stream()
    .filter(n -> n > 0)
    .limit(3)  // stops the pipeline early once 3 elements pass
    .collect(Collectors.toList());

// Why laziness matters for performance: filter+map+limit(3) on a huge
// stream only processes as many elements as needed to satisfy limit(3),
// not the entire source collection

Type	Return	Execution	उदाहरण
Intermediate	दूसरा Stream	Lazy	filter, map, sorted
Terminal	Non-stream result	Eager, पूरी pipeline चलाता है	collect, forEach, reduce

import java.util.stream.*;

List<Integer> numbers = List.of(5, 3, 8, 1, 9, 2);

Stream<Integer> pipeline = numbers.stream()
    .filter(n -> n > 2)
    .map(n -> n * 2)
    .sorted();

System.out.println('Pipeline बनी, अभी execute नहीं हुई');

List<Integer> result = pipeline.collect(Collectors.toList());  // terminal
System.out.println(result);  // [6, 10, 16, 18]

// pipeline.count();  // IllegalStateException

boolean hasLarge = numbers.stream()
    .peek(n -> System.out.println('Checking: ' + n))
    .anyMatch(n -> n > 8);
// Match मिलते ही रुक जाता है

List<Integer> firstThree = numbers.stream()
    .filter(n -> n > 0)
    .limit(3)
    .collect(Collectors.toList());

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