CODEWITHSUNDEEP
aspectj
Christian
Christian

Reputation: 6440

What do return statements do in an AspectJ advice?

The following is an excerpt from an AspectJ example:

class Point  {
      int x, y;

      public void setX(int x) { this.x = x; }
      // ...
  }

  aspect PointAssertions {

      private boolean Point.assertX(int x) {
          return (x <= 100 && x >= 0);
      }
      // ...

      before(Point p, int x): target(p) && args(x) && call(void setX(int)) {
          if (!p.assertX(x)) {
              System.out.println("Illegal value for x"); return;
          }
      }
      // ...
  }

Could someone please clarify for me what the return; statement does in the before advice - why it is (needs to be?) there and what would happen without it?

Will it basically "return form setX()" before the method body is executed?

Is there a manual page explaining it?

Upvotes: 0

Views: 124

Answers (2)

Frank Pavageau
Frank Pavageau

Reputation: 11715

To complete the answer by @LajosArpad, before advices can only change the flow by throwing an exception. The only advice that can prevent calling the advised method while retaining the same flow semantics is around, but it needs to return something itself in that case (if the return type is not void, of course).

Upvotes: 2

Lajos Arpad
Lajos Arpad

Reputation: 76884

Your code checks this:

(!p.assertX(x))

whenever the logical expression above is true, the code in its block of { } will be executed, including the return;. The point of the return statement is to make sure that the function stops and no further code will be executed. It is a common approach to do so in case of errors.

Upvotes: 1

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