Constructor Value Vs. Observer in Java

Who Belongs to Whom?

It is common to connect two components using constructor parameters. This procedure can be seen very clearly, for example, in the construction of graphic surfaces. Take the following source code:

public class SubView {
  private MainView mainView;
  public SubView(MainView mainView) {
    this.mainView = mainView;
  }
  public void buttonClicked(String input) {
    mainView.setInputValue(input);
  }
}