asCollector

asCollector(Class arrayClass, int arrayLength) は arrayType の引数を指定した数の引数のリストに変えてくれる。asSpreader はほぼその反対。

import java.lang.invoke.*;
import static java.lang.invoke.MethodType.*;
import static java.lang.invoke.MethodHandles.*;

public class AsCollectorEx {
  public static void main(String[] args) throws Throwable {
    Lookup lookup = lookup();
    MethodHandle m0 = lookup.findStatic(AsCollectorEx.class, "printAll",
        methodType(void.class, Object[].class));
    P("m0   : " + m0);
    MethodHandle mcoll = m0.asCollector(Object[].class, 4);
    mcoll = mcoll.asType(methodType(void.class, String.class, String.class, String.class, String.class));
    P("mcoll: " + mcoll);
    mcoll.invokeExact("Foo", "Bar", "Fizz", "Buzz");

    Object[] params = new Object[] {"Foo", "Bar", "Fizz", "Buzz"};
    MethodHandle mspr = mcoll.asSpreader(Object[].class, 4);
    P("mspr: " + mspr);
    mspr.invokeExact(params);
  }
  public static void printAll(Object[] args) {
    StringBuilder sb = new StringBuilder();
    sb.append("(");
    for (Object o : args) 
      sb.append(o == null ? "(null) " : o.toString() + " ");
    sb.append(")");
    System.out.println(sb.toString());
  }
  static void P(Object o) { System.out.println(o); }
}

m0   : MethodHandle(Object)void
mcoll: MethodHandle(Object,Object,Object,Object)void
(Foo Bar Fizz Buzz )
mspr: MethodHandle(Object)void
(Foo Bar Fizz Buzz )