Guice AssistedInject won't inject the factory

Question

I am trying to use Guice 3.0 AssistedInject, and it won't instantiate the factory.

SSCCE Code:

Parent class

public class ParentClass() {
  @Inject private MyFactory myFactory;
  private final Foo foo;
  private final Bar bar;
  public ParentClass() {
    if(myFactory == null) System.err.println("Error: I should have injected by now!");
    foo = myFactory.create(new Map<String, Object>());
    // etc.
  }
}

Factory Interface

public interface MyFactory {
  Foo create(Map<String, Object> mapA);
  Bar create(Map<String, Object> mapB, Map<String, Object> mapC);
}

Module

public class ParentModule extends AbstractModule {
  @Override
  protected void configure() {
    install(new FactoryModuleBuilder()
        .implement(Foo.class, FooImpl.class)
        .implement(Bar.class, BarImpl.class)
        .build(MyFactory.class));
  }

FooImpl

public class FooImpl implements Foo {
  private final Map<String, Object> mapA;
  @AssistedInject
  public FooImpl(@Assisted Map<String, Object> mapA) {
    this.mapA = mapA;
  }
}

BarImpl is very similar to FooImpl. What is going wrong here? Note also that I tried both @AssistedInject and @Inject here, both cause the error.

Output:

Error: I should have injected by now!
Exception in thread "main" com.google.inject.ProvisionException: Guice provision errors:

1) Error injecting constructor, java.lang.NullPointerException
  at ParentClass.<init>(ParentClass.java:7)
  while locating com.my.package.ParentClass

1 error
        at com.google.inject.internal.InjectorImpl$4.get(InjectorImpl.java:987)
        at com.google.inject.internal.InjectorImpl.getInstance(InjectorImpl.java:1013)
        at com.my.package.ParentMain.main(ParentMain.java:16)
Caused by: java.lang.NullPointerException
        at com.my.package.ParentClass.<init>(ParentClass.java:9)
        at com.my.package.ParentClass$$FastClassByGuice$$d4b3063a.newInstance(<generated>)
        at com.google.inject.internal.cglib.reflect.$FastConstructor.newInstance(FastConstructor.java:40)
        ... 8 more

Note that line 9 is the line of the first call to myFactory.create()

Answer 1

According to Guice's javadoc, field injection is performed after constructor injection.

I assume your ParentClass instance is created by Guice. When your ParentClass's constructor is executed, its myFactory field has not been injected yet.