Skip to content

README.md

Latest commit

 

History

History
377 lines (247 loc) · 8.44 KB

README.md

File metadata and controls

377 lines (247 loc) · 8.44 KB
Raw

Java 11 (LTS)

A comprehensive guide to all Java 11 concepts with practical examples for interview preparation.

Table of Contents

  1. HTTP Client (Standardized)
  2. Files Methods Enhancements
  3. String Methods Enhancements
  4. Optional.isEmpty()
  5. Predicate.not()
  6. Local-Variable Syntax for Lambda Parameters
  7. Nest-Based Access Control
  8. Java Flight Recorder (JFR)
  9. Epsilon Garbage Collector
  10. ZGC (Experimental)
  11. Removed Java EE and CORBA Modules
  12. Common Interview Questions

1. HTTP Client (Standardized)

The HTTP Client API is now a standard feature in Java 11 (previously in Java 9 as incubator).

Overview

The HTTP Client provides a modern, easy-to-use API for HTTP requests with support for HTTP/2 and WebSocket.

Basic Usage

import java.net.http.*;

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
    .uri(URI.create("https://api.example.com/data"))
    .build();

HttpResponse<String> response = client.send(request, 
    HttpResponse.BodyHandlers.ofString());
System.out.println(response.body());

Key Features

  • HTTP/1.1 and HTTP/2 support
  • Asynchronous and synchronous requests
  • WebSocket support
  • Better than HttpURLConnection
  • Modern API design

See HttpClientStandard.java for complete example.

2. Files Methods Enhancements

New convenience methods for reading and writing files.

Overview

Java 11 adds readString() and writeString() methods to the Files class for simplified file I/O.

Basic Usage

import java.nio.file.*;

// Read entire file as string
String content = Files.readString(Paths.get("file.txt"));

// Write string to file
Files.writeString(Paths.get("output.txt"), "Hello, Java 11!");

// With charset
String content = Files.readString(Paths.get("file.txt"), 
    StandardCharsets.UTF_8);

Key Features

  • Simplified file reading
  • Simplified file writing
  • Automatic charset handling
  • Less boilerplate code

See FilesMethods.java for complete example.

3. String Methods Enhancements

New methods for string manipulation and validation.

Overview

Java 11 adds several useful methods to the String class: isBlank(), lines(), strip(), stripLeading(), stripTrailing(), and repeat().

Basic Usage

// isBlank() - checks if string is blank (whitespace only)
String str = "   ";
boolean blank = str.isBlank(); // true

// lines() - returns stream of lines
String text = "Line 1\nLine 2\nLine 3";
text.lines().forEach(System.out::println);

// strip() - removes leading and trailing whitespace
String s = "  hello  ";
String stripped = s.strip(); // "hello"

// repeat() - repeats string
String repeated = "Java ".repeat(3); // "Java Java Java "

Key Features

  • isBlank(): Better than checking trim().isEmpty()
  • lines(): Stream of lines from multiline string
  • strip(): Unicode-aware trim
  • repeat(): Repeat string N times

See StringMethods.java for complete example.

4. Optional.isEmpty()

A more readable way to check if an Optional is empty.

Overview

isEmpty() provides a clearer alternative to !isPresent().

Basic Usage

Optional<String> optional = Optional.empty();

// Before Java 11
if (!optional.isPresent()) {
    // handle empty
}

// Java 11+
if (optional.isEmpty()) {
    // handle empty - more readable
}

Benefits

  • More readable code
  • Clearer intent
  • Better than !isPresent()

See OptionalIsEmpty.java for complete example.

5. Predicate.not()

A static method to negate predicates.

Overview

Predicate.not() provides a cleaner way to negate predicates in streams.

Basic Usage

List<String> names = Arrays.asList("Alice", "", "Bob", "  ");

// Filter non-blank strings
List<String> nonBlank = names.stream()
    .filter(Predicate.not(String::isBlank))
    .collect(Collectors.toList());

Benefits

  • Cleaner than filter(s -> !s.isBlank())
  • Method reference support
  • More readable

See PredicateNot.java for complete example.

6. Local-Variable Syntax for Lambda Parameters

The var keyword can now be used in lambda parameters.

Overview

Java 11 allows using var in lambda parameters for consistency with local variables.

Basic Usage

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");

// Using var in lambda
names.forEach((var name) -> System.out.println(name));

// With annotations
names.forEach((@NonNull var name) -> System.out.println(name));

Benefits

  • Consistency with local variables
  • Allows annotations on lambda parameters
  • Type inference still works

See VarInLambda.java for complete example.

7. Nest-Based Access Control

Improved access control for nested classes.

Overview

Nest-based access control allows classes in the same nest to access each other's private members without synthetic bridge methods.

Benefits

  • Better performance (no synthetic methods)
  • Cleaner bytecode
  • More efficient reflection
  • Better encapsulation

See NestBasedAccessControl.java for complete example.

8. Java Flight Recorder (JFR)

JFR is now open-source and available in OpenJDK.

Overview

Java Flight Recorder provides low-overhead profiling and monitoring capabilities.

Key Features

  • Low overhead profiling
  • Production-ready monitoring
  • Event collection
  • Performance analysis

See JavaFlightRecorderDemo.java for complete example.

9. Epsilon Garbage Collector

A no-op garbage collector for testing and performance analysis.

Overview

Epsilon GC does not perform any garbage collection, useful for testing memory allocation patterns.

Usage

java -XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC MyApp

Use Cases

  • Performance testing
  • Memory allocation analysis
  • Short-lived applications

10. ZGC (Experimental)

A low-latency garbage collector (experimental in Java 11).

Overview

ZGC is designed for applications requiring low latency and large heaps.

Usage

java -XX:+UnlockExperimentalVMOptions -XX:+UseZGC MyApp

Key Features

  • Low latency
  • Large heap support
  • Concurrent collection
  • Experimental in Java 11

11. Removed Java EE and CORBA Modules

Java EE and CORBA modules were removed from JDK.

Overview

These modules are now available as separate dependencies if needed.

Removed Modules

  • java.xml.ws (JAX-WS)
  • java.xml.bind (JAXB)
  • java.activation (JAF)
  • java.corba (CORBA)
  • java.transaction (JTA)
  • java.se.ee (Java SE EE)

Impact

  • Smaller JDK size
  • Use external dependencies if needed
  • Better modularity

12. Common Interview Questions

Q1: What are the key features of Java 11?

A: Key features:

  • HTTP Client (standardized)
  • Files methods (readString, writeString)
  • String methods (isBlank, lines, strip, repeat)
  • Optional.isEmpty()
  • Predicate.not()
  • Var in lambda parameters
  • Nest-based access control
  • JFR open-sourced

Q2: What is the difference between strip() and trim()?

A:

  • trim(): Removes only ASCII whitespace (≤ U+0020)
  • strip(): Removes all Unicode whitespace characters
  • stripLeading(): Removes leading whitespace
  • stripTrailing(): Removes trailing whitespace

Q3: What is HTTP Client API?

A: Modern HTTP API:

  • HTTP/1.1 and HTTP/2 support
  • Asynchronous and synchronous requests
  • Better than HttpURLConnection
  • Standardized in Java 11

Q4: What is Nest-Based Access Control?

A: Improved access control:

  • Classes in same nest can access private members
  • No synthetic bridge methods
  • Better performance
  • Cleaner bytecode

Q5: What modules were removed in Java 11?

A: Removed modules:

  • Java EE modules (JAX-WS, JAXB, etc.)
  • CORBA module
  • Available as external dependencies

Last Updated: 2025
Version: 1.0

This guide covers the features of Java 11 (LTS), released on September 25, 2018.