how can we apply aspect oriented programming on a particular line of java class ? - aspectj

Question

How can we apply aop on the last line of main method ?
Below is a test class for call by value in java. I have been asked in one interview to apply Aspect oriented programming on last line of the class. Is it possible to apply AOP on a particular line of any java class, if yes then please give some example code.
public class TestCallByValue {
public static void main(String[] args) {
Student st = new Student("Sanjeev", 1);
changeName(st);
System.out.println(st.getName());//apply aop on this line to stop printing sysout
}
public static void changeName(Student st) {
st = new Student("Rajeev", 2);
st.setName("Amit");
}
}
class Student {
String name;
Integer id;
public Student(String name, Integer id) {
this.name = name;
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
}

Answer 1

What can be applied on a particular line of java code is called a joinpoint
This link lists the possible joinpoints you can set in your code, with aspectj. As you can see, only constructor call, method call, field initialization, etc. can be defined as joinpoints
The only way is to apply a pointcut on System.out#println. You could as well encapsulate System.out.println(st.getName()); in a dedicated method

Answer 2

AspectJ doesn't operate on source code, it operates on the semantic structure of Java programs. As such, it doesn't have a concept of "lines". The interviewer meant that you should prevent a particular method call from happening, and told you where that method call is, in this particular case it's the last statement of the main method.
This statement is located in TestCallByValue.main() method and invokes println() on System.out, which is a PrintStream. While we cannot indicate to AspectJ that we want to prevent only the "last" statement from executing, we can narrow this down to
method calls to the println method of the PrintStream class, accepting a String and returning void, within the code contained in the TestCallByValue.main() method that accepts an array of Strings and returns void
To prevent the method call from happening, you will need an around advice which doesn't call proceed(). We can also check whether the target of the method call is actually System.out, so we prevent only System.out.println(String), not println(String) calls on other instances of PrintStream.
The above can be achieved with the following aspect:
aspect DummyAspect {
pointcut printlnStatementInMain(): withincode(void TestCallByValue.main(String[]))
&& call(void java.io.PrintStream.println(String));
void around(): printlnStatementInMain() {
if (thisJoinPoint.getTarget() != System.out) {
proceed();
}
}
}