Lambda/Closure7JDK8 Lambda

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JDK8 Lambda JDK8 (x -> x * 2)

(Integer x) -> x + 2

Java Lambda/Closure4 Type inference Lambda/Closure JDK8   Lambda/Closure6 
JDK8 Lambda compose

public static <A, B, C> Func<A, C> compose(Func<A, B> f, Func<B, C> g) {
    return x -> g.apply(f.apply(x));
}

Lambda/Closure6 Func ".apply" x -> g.apply(f.apply(x)) x -> g(f(x)) compose g(f(x)) f(x) = x + 2 g(y) = y * 3

compose((Integer x) -> x + 2, (Integer y) -> y * 3);

Lambda/Closure6

compose(
    new Func<Integer, Integer>() {
        public Integer apply(Integer x) {
            return x + 2;
        }
    },
    new Func<Integer, Integer>() {
        public Integer apply(Integer y) {
            return y * 3;
        }
    }
);

JDK8 Lambda token -> Lambda

//  x  y 
(int x, int y) -> x + y

//  42
() -> 42

JDK8 Lambda

// 
(String s) -> { out.println(s); }

// 
(Integer x) -> {
    Integer result;
    ...other statements
    ...
    return result;
};

Lambda JDK8 Lambda
Lambda JavaScript Function JDK8 Lambda Target typeLambda Lambda Java Lambda/Closure5 API Java Lambda JDK8 Functional interface Lambda RunnableCallableComparator

public interface Runnable {
    void run();
}

public interface Callable<V> {
    V call() throws Exception;
}

public interface Comparator<T> {
    int compare(T o1, T o2);
}

Lambda/Closure6 Func Lambda Lambda Func

Func<Integer, Integer> func = x -> x * 2;

x Method signature Lambda

public interface Function<P, R> {
    R call(P p);
}

(x -> x * 2) Function Double

Function<Double, Double> f2 = x -> x * 2;

Lambda
JDK8 @FunctionalInterface

@FunctionalInterface
public interface Func<P, R> {
    R apply(P p);
}

@FunctinalInterface

@FunctionalInterface
public interface Function<P, R> {
    R call(P p);
    R call(P p1, P p2);
}

>@FunctionalInterface ^ Function is not a functional interface multiple non-overriding abstract methods found in interface Function Lambda

import static java.lang.System.out;

public class Hello {
    Runnable r1 = new Runnable() {
        public void run() {
            out.println(this);
        }
    };
    Runnable r2 = new Runnable() {
        public void run() {
            out.println(toString());
        }
    };

    public String toString() { return "Hello, world!"; }

    public static void main(String[] args) {
        new Hello().r1.run();
        new Hello().r2.run();
    }
}

Hello$1@103368e Hello$2@1f2ae62 this toString

import static java.lang.System.out;

public class Hello {
    Runnable r1 = () -> { out.println(this); };
    Runnable r2 = () -> { out.println(toString()); };

    public String toString() { return "Hello, world!"; }

    public static void main(String[] args) {
        new Hello().r1.run();
        new Hello().r2.run();
    }
}

"Hello, world!"Lambda this toString Hello compose final Lambda/Closure5 Java finalJDK8 final Lambda final
Lambda JavaScript Scala Free variableJDK8 Lambda JDK8 Lambda
JDK8 Lambda API Java Lambda Java API