When does Java require explicit type parameters?

Question

Given:

import com.google.common.collect.ImmutableMap;
import java.util.function.Function;
import java.util.stream.Collector;
import java.util.stream.Stream;
         


        

Answer 1

There's another way to fix this. You can give a hint to compiler explicitly specifying the argument type for identity lambda:

ImmutableMap map2 = Stream.of("1", "2", "3")
    .collect(Testcase.toImmutableMap((String i) -> i, Integer::valueOf).build());

Compiles fine in Javac 1.8.0_25 and ECJ 3.10.2.