Java 8 Features

// Lambda example
(a, b) -> a + b;

// Stream example
list.stream().filter(x -> x > 10).collect(Collectors.toList());

import java.util.*;
import java.util.stream.*;

public class Main {

  public static void main(String[] args) {

    List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);

    // Lambda
    numbers.forEach(n -> System.out.println(n));

    // Stream API
    List<Integer> result = numbers.stream()
        .filter(n -> n % 2 == 0)
        .map(n -> n * n)
        .collect(Collectors.toList());

    System.out.println(result);

    // Optional
    Optional<String> name = Optional.of("Java 8");
    System.out.println(name.orElse("Empty"));

  }
}

// Output:
// 1 2 3 4 5 6
// [4, 16, 36]
// Java 8

• 1 Lambda Expressions
• 2 Streams API
• 3 Functional Interfaces
• 4 Optional Class
• 5 Default Methods in Interfaces

• 1 Short way to write anonymous functions.
• 2 Used with functional interfaces.
• 3 Improves readability.
• 4 Used in Streams API.

• 1 Process collections in functional style.
• 2 Supports filter, map, reduce.
• 3 Lazy evaluation.
• 4 Supports parallel processing.

• 1 Default and static methods in interfaces.
• 2 Date and Time API improvements.
• 3 Nashorn JavaScript engine.
• 4 Improved Optional handling.

• 1 Used in modern backend development.
• 2 Used in microservices architecture.
• 3 Used in data processing pipelines.
• 4 Used in enterprise applications.
• 5 SaaS products use Java 8 Features in services, dashboards, background jobs, and API workflows.
• 6 ERP and banking systems apply Java 8 Features with validation, logging, review, and rollback plans.
• 7 E-commerce and healthcare platforms use Java 8 Features carefully because reliability and data correctness matter.

• 1 A Java program first evaluates the surrounding context, then applies the Java 8 Features rules to the current data.
• 2 The important mental model is input, transformation, result, and failure path.
• 3 In production, the same flow usually sits inside a larger layer such as a controller, service, repository, job, or UI component.

• 1 Choose the simplest implementation first, then measure real workloads.
• 2 Watch for repeated work inside loops, unnecessary allocations, and slow I/O in hot paths.
• 3 Prefer clear data structures and stable APIs before micro-optimizing syntax.

• 1 Treat external input as untrusted until it is validated.
• 2 Avoid hardcoded secrets and never print sensitive values in examples or logs.
• 3 Use established libraries for authentication, encryption, parsing, and database access.

• 1 Overusing streams for simple logic.
• 2 Writing complex lambdas.
• 3 Ignoring performance in parallel streams.
• 4 Misusing Optional class.
• 5 Skipping the small working example before adding framework code.
• 6 Ignoring null, empty, duplicate, and boundary inputs.
• 7 Mixing business logic, input handling, and output formatting in one place.
• 8 Using broad error handling that hides the real failure.
• 9 Forgetting to test the behavior after refactoring.
• 10 Adding clever code that future maintainers will struggle to read.

• 1 Use lambda for simple logic.
• 2 Use Streams for collection processing.
• 3 Use Optional to avoid null.
• 4 Keep code readable and clean.
• 5 Start with clear requirements and one minimal working example.
• 6 Use meaningful names that explain business intent.
• 7 Keep examples small enough to debug line by line.
• 8 Validate input at every trust boundary.
• 9 Handle errors explicitly and preserve useful context.
• 10 Prefer simple control flow over deeply nested logic.
• 11 Separate domain logic from I/O and framework code.
• 12 Write tests for normal, boundary, and failure cases.
• 13 Review security assumptions before production use.
• 14 Measure performance before optimizing.
• 15 Document non-obvious decisions close to the code or in project notes.
• 16 Use official documentation when behavior is version-specific.
• 17 Keep dependencies current and remove unused code.
• 18 Avoid hardcoded secrets, credentials, and environment-specific paths.
• 19 Log operational events without exposing sensitive data.
• 20 Design examples so learners can safely modify and rerun them.

• 1 Beginner: rewrite the example with different names and values.
• 2 Intermediate: add validation and handle one expected failure case.
• 3 Advanced: place Java 8 Features inside a small service-style design with tests.

• 1 Build a small Java console feature that demonstrates Java 8 Features.
• 2 Accept input, process it with the concept, print a clear result, and handle invalid input.
• 3 Add a README note explaining the design choice and two edge cases you tested.

• 1 If the program does not compile, check spelling, imports, braces, and file/class names first.
• 2 If output is unexpected, print intermediate values and verify each branch of the logic.
• 3 If the design feels complex, reduce it to the smallest working example and add pieces back one at a time.

• 1 Practice Java 8 Features with a second example from a business domain such as inventory, payroll, banking, or e-commerce.
• 2 Review related Java topics that cover data flow, error handling, testing, and clean design.
• 3 Compare your solution with official documentation and simplify anything you cannot explain clearly.