core/play/src/main/java/play/inject/BindingKey.java
public Binding<T> to(final BindingKey<? extends T> key) {
    return underlying.to(key.asScala()).asJava();
  }
public Binding<T> to(final BindingKey<? extends T> key) {
    return underlying.to(key.asScala()).asJava();
  }
Bind this binding key to another binding key.