What is Java Stream API
💡 Concept: Java Stream API
Java Stream API introduced in Java 8 provides a modern, functional approach to processing collections and sequences of elements.
📘 Quick Intro
Stream API supports functional-style operations like map, filter, reduce, and allows easy parallelization.
🧠 Analogy
Think of a Stream as a conveyor belt that moves data through a series of processing steps, transforming or filtering elements as they flow along.
🔧 Technical Explanation
- Streams do not store data but operate on data source collections.
- Supports lazy evaluation for efficiency.
- Allows chained operations for concise code.
- Parallel streams allow multi-core processing without explicit thread management.
- Common operations: filter, map, reduce, collect, forEach.
🎯 Use Cases
- ✅ Processing collections with concise code.
- ✅ Data filtering and transformation.
- ✅ Parallel data processing for performance.
💻 Example Code: Using Java Stream API
import java.util.*;
import java.util.stream.*;
public class StreamExample {
public static void main(String[] args) {
List list = Arrays.asList("Java", "Python", "JavaScript", "C#", "Java");
// Filter and print distinct elements
list.stream()
.filter(s -> s.startsWith("J"))
.distinct()
.forEach(System.out::println);
}
}
❓ Interview Q&A
Q1: What is Java Stream API?
A: A functional programming abstraction to process collections.
Q2: Are streams mutable?
A: No, streams do not modify underlying data.
Q3: What is lazy evaluation in streams?
A: Operations are evaluated only when terminal operations are invoked.
Q4: How to create a parallel stream?
A: Using parallelStream() method.
Q5: What is the difference between map and flatMap?
A: map transforms elements; flatMap flattens nested streams.
Q6: Can streams be reused?
A: No, streams cannot be reused after terminal operation.
Q7: What are terminal operations?
A: Operations that produce a result or side-effect, e.g., forEach, collect.
Q8: How do streams improve performance?
A: Enable parallel processing.
Q9: What is a pipeline in Stream API?
A: A sequence of operations chained together.
Q10: Are streams thread-safe?
A: Depends on the source, not inherently thread-safe.
📝 MCQs
Q1. What is Java Stream API?
- A database
- A GUI toolkit
- A functional programming abstraction to process collections
- None
Q2. Are streams mutable?
- Yes
- No
- Sometimes
- Always
Q3. What is lazy evaluation?
- Evaluated immediately
- Evaluated at terminal operation
- Never evaluated
- Always evaluated
Q4. How to create a parallel stream?
- Using stream()
- Using parallelStream()
- Using forEach()
- None
Q5. Difference between map and flatMap?
- Both same
- map transforms; flatMap flattens
- map flattens; flatMap transforms
- None
Q6. Can streams be reused?
- Yes
- No
- Sometimes
- Always
Q7. What are terminal operations?
- Intermediate operations
- Terminal operations
- Stream creation
- None
Q8. How do streams improve performance?
- Single thread only
- Enable parallel processing
- Slow down
- None
Q9. What is a pipeline?
- Unrelated operations
- Sequence of chained operations
- Random operations
- None
Q10. Are streams thread-safe?
- Yes
- No
- Depends on source
- Always
💡 Bonus Insight
Java Stream API revolutionized collection processing with its functional, concise, and parallel-friendly design.
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