Java Streams (Java 8+)

Java Streams were introduced in Java 8 to simplify data processing on collections by providing a declarative, functional-style API.

Streams are not data structures —
they are operations performed on data.

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Why Streams Were Introduced

Before Java 8:

• Data processing required loops
• Code was verbose and error-prone
• Parallel processing was complex

Streams solve this by providing:

• Clean and readable code
• Internal iteration
• Built-in parallelism
• Functional programming style

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What Is a Stream?

A Stream is a sequence of elements from a source that supports data processing operations.

Important Clarification

• Streams do not store data
• Streams operate on data from a source
• Source can be:
  • Collection
  • Array
  • I/O channel

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Characteristics of Streams

• Streams do not modify the source
• Streams are not reusable
• Streams support lazy evaluation
• Streams process elements only when needed
• Streams support parallel execution

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Internal Iteration

Collections:

for (String s : list) { }

Streams:

list.stream().filter(…).map(…);

✔ Iteration handled internally
✔ Less boilerplate
✔ Safer parallel execution

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Stream Pipeline Structure

A stream pipeline consists of:

• Source
• Intermediate operation(s)
• Terminal operation

Source → Intermediate Ops → Terminal Op

Without a terminal operation:

• Nothing executes.