Java.Java8.What are terminal methods and what are not ?

✅ 1. Intermediate Methods (NOT terminal)

• These build up the stream pipeline
• Lazy – they don’t do anything until a terminal method is called
• Always return a Stream (or IntStream, etc.)

🔹 Examples:

filter(), map(), flatMap(), sorted(), distinct(), limit(), skip(), peek()

These methods transform the stream and are usually chained.

✅ 2. Terminal Methods (Trigger execution)

• These finalize the stream
• Consume the pipeline and produce a result
• Can return a value or cause a side effect
• After a terminal method is called, the stream is closed and can’t be reused

🔹 Examples:

Group	Methods
Reduction	collect(), reduce(), count(), sum(), min(), max(), average()
Iteration	forEach(), forEachOrdered()
Matching	anyMatch(), allMatch(), noneMatch()
Finding	findFirst(), findAny()
Conversion	toArray()

🧠 Think of It Like This:

Stream Operation	Does it return a stream?	Is it lazy?	Is it terminal?
.map()	✅ Yes	✅ Yes	❌ No
.filter()	✅ Yes	✅ Yes	❌ No
.sorted()	✅ Yes	✅ Yes	❌ No
.limit()	✅ Yes	✅ Yes	❌ No
.forEach()	❌ No (returns void)	❌ No	✅ Yes
.collect()	❌ No (returns result)	❌ No	✅ Yes
.count()	❌ No	❌ No	✅ Yes

“Terminal methods start the pipeline execution.”

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🔹 Think of a stream pipeline like a water pipe:

• Intermediate methods = assembling and configuring the pipe (filters, twists, splits)
• Terminal method = turning on the faucet 💧 — only then the water (data) flows

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✅ Why Terminal Methods Trigger Everything

• Streams in Java are lazy — intermediate methods do nothing until a terminal method is called.
• Terminal methods pull the data through all intermediate steps.

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🔸 Real-World Analogy

Let’s say you’re building a factory line:

List<String> items = List.of("apple", "banana", "avocado");

items.stream()                 // define the conveyor belt
     .filter(s -> s.startsWith("a"))   // step 1: filter
     .map(String::toUpperCase);        // step 2: transform

Nothing happens yet! 😴

But once you call:

     .forEach(System.out::println);    // terminal: run the machine!

Now everything kicks in.

✅ Summary:

🔧 Intermediate Methods	🚀 Terminal Methods
Just configure the stream	Execute and produce results
Return a stream	Return a value / side effect
Lazy — do nothing alone	Start processing