All of these things are useful and valid techniques for building scalable, maintainable and extensible code.
Abstract is a pretty basic OO concept. You make an abstract class when you want it to be derived and never used directly.
Singleton is where a class can only ever create one object. Harder than it sounds.
Proxy is where the class interfaces with something else. Again, very useful. Proxies are used by Spring to implement AOP.
Factory - abstracts away the creation of objects, in other words the client object does not need to know how to create objects. It's used extensively in the Spring IoC container.
Beans are object that use simple but powerful conventions of creating reusable components in Java.
Interceptors at used by AOP.
If you use these concepts as they are intended to be used then your code will be cleaner, maintainable and a joy to work with.
Abstract is a pretty basic OO concept. You make an abstract class when you want it to be derived and never used directly.
Singleton is where a class can only ever create one object. Harder than it sounds.
Proxy is where the class interfaces with something else. Again, very useful. Proxies are used by Spring to implement AOP.
Factory - abstracts away the creation of objects, in other words the client object does not need to know how to create objects. It's used extensively in the Spring IoC container.
Beans are object that use simple but powerful conventions of creating reusable components in Java.
Interceptors at used by AOP.
If you use these concepts as they are intended to be used then your code will be cleaner, maintainable and a joy to work with.