# Idioms

## Introduction

This chapter consists of very short snippets of AspectJ code, typically pointcuts, that are particularly evocative or useful. This section is a work in progress.

Here's an example of how to enfore a rule that code in the java.sql package can only be used from one particular package in your system. This doesn't require any access to code in the java.sql package.

    /* Any call to methods or constructors in java.sql */
    pointcut restrictedCall():
        call(* java.sql.*.*(..)) || call(java.sql.*.new(..));

    /* Any code in my system not in the sqlAccess package */
    pointcut illegalSource():
        within(com.foo..*) && !within(com.foo.sqlAccess.*);

    declare error: restrictedCall() && illegalSource():
        "java.sql package can only be accessed from com.foo.sqlAccess";

Any call to an instance of a subtype of AbstractFacade whose class is not exactly equal to AbstractFacade:

    pointcut nonAbstract(AbstractFacade af):
        call(* *(..))
        && target(af)
        && !if(af.getClass() == AbstractFacade.class);

If AbstractFacade is an abstract class or an interface, then every instance must be of a subtype and you can replace this with:

    pointcut nonAbstract(AbstractFacade af):
        call(* *(..))
        && target(af);

Any call to a method which is defined by a subtype of AbstractFacade, but which isn't defined by the type AbstractFacade itself:

    pointcut callToUndefinedMethod():
         call(* AbstractFacade+.*(..))
         && !call(* AbstractFacade.*(..));

The execution of a method that is defined in the source code for a type that is a subtype of AbstractFacade but not in AbstractFacade itself:

    pointcut executionOfUndefinedMethod():
        execution(* *(..))
        && within(AbstractFacade+)
        && !within(AbstractFacade)