method-reference

Why this doesn't work? I get compiler error "Cannot make static reference to the non static method print..." public class Chapter3 { public void print(String s) { System.out.println(s); } public static void main(String[] args) { Arrays.asList("a", "b", "c").forEach(Chapter3::print); } } Regardless of whether you use method references, lambda expressions or ordinary method calls, an instance method requires an appropriate instance for the invocation. The instance may be supplied by the function invocation, e.g. if forEach expected a BiConsumer<Chapter3,String> it worked. But since forEach

I'm learning how to use stream, and I get a problem with this method. public static String[] inArray(String[] array1, String[] array2) { return Arrays.stream(array1) .filter(str -> Arrays.stream(array2).anyMatch(s -> s.contains(str))) .distinct().sorted().toArray(**String[]::new**); } I'm so confused about String[]::new , could you give me a hint? String[]::new means size -> new String[size] . When Stream#toArray(IntFunction<A[]> generator) is ready to produce an array, it calls generator and passes ( generator.apply ) the size of the inner collection to get a collection to fill it up. String[

Currently getting into Java 8 lambda expressions and method references. I want to pass a method with no args and no return value as argument to another method. This is how I am doing it: public void one() { System.out.println("one()"); } public void pass() { run(this::one); } public void run(final Function function) { function.call(); } @FunctionalInterface interface Function { void call(); } I know there is a set of predefined functional interfaces in java.util.function such as Function<T,R> but I didn't find one with no arguments and not producing a result. It really does not matter;

I just had a rather unpleasant experience in our production environment, causing OutOfMemoryErrors: heapspace.. I traced the issue to my use of ArrayList::new in a function. To verify that this is actually performing worse than normal creation via a declared constructor ( t -> new ArrayList<>() ), I wrote the following small method: public class TestMain { public static void main(String[] args) { boolean newMethod = false; Map<Integer,List<Integer>> map = new HashMap<>(); int index = 0; while(true){ if (newMethod) { map.computeIfAbsent(index, ArrayList::new).add(index); } else { map

It's possible to chain/concatenate what is done with elements in a lambda expression like this: list.forEach(s -> { System.out.println(s.toLowerCase()); System.out.println(s.toUpperCase()); }); Is there a way to do this also with method references? Something like this: list.forEach({ System.out::println(String::toLowerCase); System.out::println(String::toCase); }); I know I could do this in four separate calls (which do also more, that is mutate the values): list.replaceAll(String::toLowerCase); list.forEach(System.out::println); list.replaceAll(String::toUpperCase); list.forEach(System.out:

What am I missing? Why do I have to use Object::toString below and not Integer::toString ? Does it have anything to do with type erasure with generics? Arrays.asList(1,2,3).stream().map(Integer::toString).forEach(System.out::println); //Won't compile Arrays.asList(1,2,3).stream().map(Object::toString).forEach(System.out::println); //Compiles and runs fine This has nothing to do with type erasure. Look at the error message : (argument mismatch; invalid method reference reference to toString is ambiguous both method toString(int) in Integer and method toString() in Integer match) The Integer