the exercise file for Exercise 4.3 should not already contain solution.

Hello,

could you please exaplain once again what's the difference between non-lambda code and it's lambda version? (Chapter 7: Testing, Debugging and Refactoring, site 98)

non-lambda code:

Logger logger = new Logger();
if (logger.isDebugEnabled()) {
 logger.debug("Look at this: " + expensiveOperation());
}

lambda code:

Logger logger = new Logger();
logger.debug(() -> "Look at this: " + expensiveOperation());

What do we win by using the lambda version? We can hide the isDebugEnabled check in non-lambda code as well - don't we?

Hi !

I am reading your book.
I am a little confused about the writing here.

src/main/java/com/insightfullogic/java8/examples/chapter1/Album.java

public Album(String name, List<Track> tracks, List<Artist> musicians) {
    Objects.requireNonNull(name);
    Objects.requireNonNull(tracks);
    Objects.requireNonNull(musicians);      
    this.name = name;
    this.tracks = new ArrayList<>(tracks);
    this.musicians = new ArrayList<>(musicians);
}

Is it correct to write like this:

public Album(String name, List<Track> tracks, List<Artist> musicians) {
    Objects.requireNonNull(name);
    Objects.requireNonNull(tracks);
    Objects.requireNonNull(musicians);      
    this.name = name;
    this.tracks = tracks;
    this.musicians = musicians;
}

or

public Album(String name, List<Track> tracks, List<Artist> musicians) {
    this.name = Objects.requireNonNull(name);
    this.tracks = Objects.requireNonNull(tracks);
    this.musicians = Objects.requireNonNull(musicians); 
}

This git repository contains support material for the Java 8 Lambdas book.

Tiny URL Link to the book is not working.

ChatVerticle、User etc

Artist#copy
public Artist copy() {
List members = getMembers().map(Artist::copy).collect(toList());
return new Artist(name, members, nationality);
}

self invoke, and fall into an infinite loop

Hi,
Recently I'm reading this book, and now encountered some problems. When I run com.insightfullogic.java8.answers.chapter6.OptimisationExampleFixed , it hint

No matching benchmarks. Miss-spelled regexp?
Use EXTRA verbose mode to debug the pattern matching.

What's wrong? how to solve it?

This code in chapter 5 is not correct:
public long fibonacci(int x) { return cache.computeIfAbsent(x, n -> fibonacci(n-1) + fibonacci(n-2)); }
because you are not allowed to change the cache when you are using computeIfAbsent()

Exception in thread "main" java.util.ConcurrentModificationException

import org.openjdk.jmh.Main;
import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.runner.RunnerException;

jdk8
f.fibonacci(15);
result:
{0=0, 1=1, 2=1, 3=2, 4=3, 5=5, 6=8, 7=13, 8=21, 9=34, 10=55, 11=89, 12=144, 13=233}

cache = new HashMap<>(); // Lack 14,15 why？
cache = new TreeMap<>(); // use TreeMap ok

The Artist#isFrom(String nationality) method always returns true. The this keyword has to be used when pointing the class member.

The sum of sqaures of numbers in [0, 1,000,000) should be 333332833333500000, but the excercise code below gives 584144992.

https://github.com/RichardWarburton/java-8-lambdas-exercises/blob/master/src/main/java/com/insightfullogic/java8/exercises/chapter6/OptimisationExample.java

Should use LongStream and long instead.

The link entitled "Java 8 Lambdas" leads to a github 404 page.

this issues occurs when i calculate array size,
this array about three minion arays,i hava 2G heap.this file is only 40m,and if i use no parallel,this
program only uses 50m, Ask,what's the cause

static void useStream(){
    long uniqueWord = 0;
    try (Stream<String> lines =
                 Files.lines(Paths.get("D:\\nlp\\dictionary\\CoreNatureDictionary.ngram.txt"), Charset.defaultCharset())){
        long start = System.currentTimeMillis();
        uniqueWord = lines.flatMap(line -> Arrays.stream(line.split(" "))).parallel().distinct().count();

// uniqueWord = lines.flatMap(line -> Arrays.stream(line.split(" "))).distinct().count();
System.out.println(uniqueWord);
long end = System.currentTimeMillis();

        System.out.println( (end-start)+"ms");
    }catch (IOException e){
        e.printStackTrace();
    }
}