Callback method parameter annotation @ClassRef

Callback parameter annotated with @ClassRef will be assigned with a reference to the class where the method being executed is defined.

Declaration type

Callback parameter annotated with @ClassRef should be declared as java.lang.Class.

In which callbacks can be used

Parameter annotated with @ClassRef can be used in any callback.

Notes on using @ClassRef vs @This

Use @ClassRef when applying probe to static methods, because @This is null in that case.

When applying probe to non-static methods, you can either use @ClassRef or call getClass() method of the object passed via @This.

However, please note the difference: the class returned by getClass() method will be the actual class of the object whose method is running, while @ClassRef will give the class where the method is defined. The result will be different if the method is defined in a base class and is not overridden in derived classes.

Example:

package com.foo;

class Base {
  void f() {...}
  void g() {...}
}

class Derived extends Base {
 // f() is overridden, g() is not overridden
 void f() {...}
}

...

@MethodPattern("foo.bar.*:*(*)")
public class MyProbe {
  public static void onEnter(@This Base _this, @ClassRef Class _class) {
    System.out.println(_this.getClass());
    System.out.println(_class);
  }
}

...

Derived obj = new Derived();

// Applying MyProbe to this call will print:
// class com.foo.Derived
// class com.foo.Derived
obj.f();

// Applying MyProbe to this call will print:
// class com.foo.Derived
// class com.foo.Base
obj.g();