Question

I’m working in a Java framework which is trying to model a Cobol system. I have a class StudentRecord with many attributes.

class StudentRecord extend BaseRecord {
...
 public CobolString firstName;
 public CobolString lastName;
...
}

class CobolString {
...
 private String content;
 public setValue(String str){
 content = str;
}

}

Let say I have an instanse studentA of type StudentRecord with firstName value in String is ‘Max’. I want to update attribute firstName to ‘John’ using Java reflection. Normally, I do it as below:

Class  aClass = studentA.class;
Field field = aClass.getField("firstName");
field.set(studentA, new CobolString("John"));

Because this framework is to model Cobol, it have some weird behaviors and requirements. One of these is that I need to use method setValue() of CobolString to set new value for firstName to be assured that the system works.

For example: without reflection, it require me to do:

studentA.firstName.setValue("John");

With reflection, if I code that way, studentA still has new firstName, but it become a stranger to other object/method and cant work with others!!!

So how can I do the same thing using Java reflection to set new value for firstName. I mean how I get sub object firstName from parent object studentA and then invoke method “setValue” on it with new value “John”.

Thanks for help.

Answer 1

You can access the fields of an instance using reflection:

StudentRecord obj;
Field field = obj.getClass().getField("firstName"); // or StudentRecord.class.getField()
CobolString cs = (CobolString)field.get(obj);
cs.setValue("John");

If the field is private, execute this before calling Field.get():

field.setAccessible(true);