For languages which didn't have function-pointers as a first-class construct (like Java), you had to create another way to delegate functions between different

For languages which didn't have function-pointers as a first-class construct (like Java), you had to create another way to delegate functions between different objects. A way to encapsulate them, if you like. It may not seem novel now, but it was not obvious to everyone at that time that this was a possible design-pattern.