Access Class Variable on general Object of that class

Question

I have a lots of classes for example this one:

public class DepartmentST {
    public Long id = null;
    public String name = null;
    public String comments = null;
    public Long[] profiles = null;
    public Boolean default_val = false;
}

In main class I create objects of those classes and sent it to general method for example:

DepartmentST mydepartment = new DepartmentST();
generalMethod(mydepartment);

In general Method I want to access to object fields (this my question how?)

public generalMethod(Object myObj) {
    Field[] fields = myObj.getClass().getFields();
    for(Field field : fields) {
        String fieldName = field.getName();
        // I want to access that field how can i tell myObj.fielName ?
    }
}

I'm new in Java I don't know it's stupid question or not.

thanks for any help in advance.

possible duplicate of [Reflection generic get field value](http://stackoverflow.com/questions/13400075/reflection-generic-get-field-value) — Luiggi Mendoza, Mar 03 '14 at 08:10
You mean like http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Field.html#setInt(java.lang.Object, int) — Scary Wombat, Mar 03 '14 at 08:10
It looks like a design smell to me. Why doesn't the method take a DepartmentST as argument? Or at least a reference to a superclass or interface common to all objects? What should this general method do? Why are you using public fields? — JB Nizet, Mar 03 '14 at 08:12
@LuiggiMendoza you mean I can access it by field.get(myObj)? — Mohse Taheri, Mar 03 '14 at 08:17
This is a good example of misusing reflection. You should better define a base class or a common interface. — Kai, Mar 03 '14 at 08:19
@LuiggiMendoza thanks it works :) how can I thank you and mark as answer your comment? — Mohse Taheri, Mar 03 '14 at 08:21
It is not my answer, it is a duplicate Q/A. I never posted an answer. — Luiggi Mendoza, Mar 03 '14 at 08:22

score 1 · Accepted Answer · answered Mar 03 '14 at 08:20

see http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/Field.html#get(java.lang.Object)

public generalMethod(Object myObj) {
    Field[] fields = myObj.getClass().getFields();
    for(Field field : fields) {
        String fieldName = field.getName();
        // I want to access that field how can i tell myObj.fielName ?

        Class c = field.getType();
        if (c instanceOf Integer) {
            Integer value = field.getInt (myObj);
        }

        // or

        Object value = field.get (myObj); 

    }
}

I've just read your [comment](http://stackoverflow.com/questions/22141582/access-class-variable-on-general-object-of-that-class#comment33596804_22141615) and want to tell you my full ack ;-) — Kai, Mar 03 '14 at 08:22

score -1 · Answer 2 · answered Mar 03 '14 at 08:10

-1

You need to "cast" the object to a DepartmentST object:

if (myObj instanceof DepartmentST) {
    DepartmentST department = (DepartmentST) myObj;
    // continue with code

Then use that object instead of myObj.

answered Mar 03 '14 at 08:10

uyuyuy99

353
4
11

And do an `instanceof` check before. – Kai Mar 03 '14 at 08:11
there are a lot of classes, How can I tell this is DepartmentST or ProfileST? – Mohse Taheri Mar 03 '14 at 08:12
@LuiggiMendoza The OP doesn't say he wants to use reflection! He wants to access the member variable. And this answer shows how to do it better without reflection. – Kai Mar 03 '14 at 08:12
@user714965 did you at least read the code? If you did, do you know about reflection classes like `Class` and `Field`? – Luiggi Mendoza Mar 03 '14 at 08:13
@LuiggiMendoza I guess he doesn't know better – Kai Mar 03 '14 at 08:13
@MohseTaheri you can tell this by the `instanceof` check. See the edited answer. – Kai Mar 03 '14 at 08:15
1

ppl don't usually jump in and use reflection unless there is a need. – Scary Wombat Mar 03 '14 at 08:15
When using reflection you have the advantage to **not need** to know which class are you working with directly, the code will work for every object reference (even object references from `Object`!). So, this code may be used for lot of classes, you surely don't want to have lot of `if (myObj instanceof Foo) { ... } else if (myObj instanceof Bar) { ... } ... ` and on... – Luiggi Mendoza Mar 03 '14 at 08:16
By the way, just read OP's code and the possible duplicate Q/A to understand how to solve this problem with 1 line of code... – Luiggi Mendoza Mar 03 '14 at 08:17

score -1 · Answer 3 · answered Mar 03 '14 at 08:11

-1

Basically this code breaks the encapsulation. You need private fields, and you access them through getters and setters. Reflection is another way to go (depending on the context).

answered Mar 03 '14 at 08:11

sergiu

389
1
7

Not downvoter, but OP's already using reflection. Check the posted code one more time... – Luiggi Mendoza Mar 03 '14 at 08:13

Access Class Variable on general Object of that class

3 Answers3