Joinpoint VS ProceedingJoinPoint in AOP using aspectJ?

@Around("execution(* com.mumz.test.spring.aop.BookShelf.addBook(..))")

It means before calling com.mumz.test.spring.aop.BookShelf.addBook method aroundAddAdvice method is called. After System.out.println("Book being added is : " + object); operation is completed . it will call your actual method addBook(). pjp.proceed() will call addBook() method.

An around advice is a special advice that can control when and if a method (or other join point) is executed. This is true for around advices only, so they require an argument of type ProceedingJoinPoint, whereas other advices just use a plain JoinPoint. A sample use case is to cache return values:

private SomeCache cache;

@Around("some.signature.pattern.*(*)")
public Object cacheMethodReturn(ProceedingJoinPoint pjp){
    Object cached = cache.get(pjp.getArgs());
    if(cached != null) return cached; // method is never executed at all
    else{
        Object result = pjp.proceed();
        cache.put(pjp.getArgs(), result);
        return result;
    }
}

In this code (using a non-existent cache technology to illustrate a point) the actual method is only called if the cache doesn't return a result. This is the exact way the Spring EHCache Annotations project works, for example.

Another specialty of around advices is that they must have a return value, whereas other advice types must not have one.