method-reference

问题 I have an async method with a completeablefuture result: public CompletableFuture<DogLater> asyncDogLater(String dogName){} I have a list of dogs: List<Dog> dogs; Now, I want to create a map from the dog's name to the Completeablefuture: Map<String, CompletableFuture<DogLater>> map; After checking this and this I was trying to do so: Map<String, CompletableFuture<DogLater>> completableFutures = dogs.stream() .collect( Collectors.toMap(Dog::getName, asyncDogLater(Dog::getName ))); But the

问题 I have an async method with a completeablefuture result: public CompletableFuture<DogLater> asyncDogLater(String dogName){} I have a list of dogs: List<Dog> dogs; Now, I want to create a map from the dog's name to the Completeablefuture: Map<String, CompletableFuture<DogLater>> map; After checking this and this I was trying to do so: Map<String, CompletableFuture<DogLater>> completableFutures = dogs.stream() .collect( Collectors.toMap(Dog::getName, asyncDogLater(Dog::getName ))); But the

问题 Consider below code, interface TestInter { public void abc(); } class DemoStatic { public static void testStatic(String abc) { System.out.println(abc); } public void runTest () { // Using lambda expression. String str = "demo string" ; TestInter demo1 = () -> DemoStatic.testStatic(str); demo1.abc(); // Using method reference. TestInter demo2 = DemoStatic::testStatic; // This line is not compiling. demo2.abc(); } } We can invoke the testStatic method as body of TestInter interface's abc()

问题 I have an example Java code using method reference that I want to rewrite to Kotlin. Java version is using method reference, solution is short and clear. But on the other hand I cannot use method reference in Kotlin. The only version that I've managed to write is one presented below. It seems like Function3 { s: String, b: Boolean, i: Int -> combine(s, b, i) } could be written in cleaner way (if possible method reference would be perfect). I'm new to Kotlin so I'll be grateful for any clues.

问题 Method Reference for a specific method in Java 8 can be obtained as Class::Method . But how to get the method reference of all methods of a class? All the desired methods have different method names, but the same type signature. Also, the names of the methods is not known before hand. Example: class Test { public static double op0(double a) { ... } public static double op1(double a) { ... } public static double op2(double a) { ... } public static double op3(double a) { ... } public static

问题 When trying to compile the expression Comparator.comparing(String::toLowerCase) , the Java Compiler returns an error. See the following question for more information: Why Comparator.comparing doesn't work with String::toLowerCase method reference? I have tried to reduce the problem as much as possible. In particular, I have removed almost all dependencies to other classes. The main method contains two method invocations. The first statement compiles without errors, whereas the second

问题 public class Main { interface Capitalizer { public String capitalize(String name); } public String toUpperCase() { return "ALLCAPS"; } public static void main(String[] args) { Capitalizer c = String::toUpperCase; //This works c = Main::toUpperCase; //Compile error } } Both are instance methods with same signature. Why does one work and the other doesn't? Signature of String::toUpperCase : String toUpperCase(); 回答1: There are 3 constructs to reference a method: object::instanceMethod Class:

问题 The code below contains a reference to Enum::name (notice no type parameter). public static <T extends Enum<T>> ColumnType<T, String> enumColumn(Class<T> klazz) { return simpleColumn((row, label) -> valueOf(klazz, row.getString(label)), Enum::name); } public static <T, R> ColumnType<T, R> simpleColumn(BiFunction<JsonObject, String, T> readFromJson, Function<T, R> writeToDb) { // ... } Javac reports a warning during compilation: [WARNING] found raw type: java.lang.Enum missing type arguments

问题 The code below contains a reference to Enum::name (notice no type parameter). public static <T extends Enum<T>> ColumnType<T, String> enumColumn(Class<T> klazz) { return simpleColumn((row, label) -> valueOf(klazz, row.getString(label)), Enum::name); } public static <T, R> ColumnType<T, R> simpleColumn(BiFunction<JsonObject, String, T> readFromJson, Function<T, R> writeToDb) { // ... } Javac reports a warning during compilation: [WARNING] found raw type: java.lang.Enum missing type arguments

问题 I have this class called Container : public class Container { private final Map<String, Object> map = new HashMap<>(); public void put(String name, Object value) { map.put(name, value); } public Container with(String name, Object value) { put(name, value); return this; } public Object get(String name) { return map.get(name); } public <R> R get(String name, Function<Object, R> mapper) { Object value = get(name); if (null == value) { return null; } return mapper .apply(value); } public <R> R