How to create class object from class name and and use it for method overloading

Question

To explain problem consider I have 6 classes

ClassOne
ClassTwo
ClassThree
ClassFour
ClassFive
ClassImpl

I have method startOperation(List<String> classNameList), in this method I am iterating classNameList and for every class name I am using reflection to get object of the that class now I want to call method doOperation() which is an overloaded method.

private void doOperation(ClassOne objClassOne) {
    //Do somethig
}

private void doOperation(ClassTwo objClassTwo) {
    //Do somethig
}
.. And so on up to

private void doOperation(ClassFive objClassFive) {
    //Do somethig
}

my startOperation method looks like:

public void startOperation(List<string> classNameList) {
    for (String string : classNameList) {
        Class actualClass = Class.forName(className);
        Object classObj = actualClass.newInstance();
        doOperation(classObj); // here I am getting problem                             
    }
}

please tell how to call overloaded method from within the loop.

Note: classNameList dynamically contain names of different classes I don't want to hard code anything as some classes may get added to project or some may get removed I just want to add or delete respective doOperation method when this happen.

what problem are you getting?

Scary Wombat
– Scary Wombat

2014-09-01 08:24:07 +00:00
Commented Sep 1, 2014 at 8:24 — Scary Wombat
– Scary Wombat, Commented Sep 1, 2014 at 8:24
please show us the specific error which you are getting

Sagar D
– Sagar D

2014-09-01 08:25:05 +00:00
Commented Sep 1, 2014 at 8:25 — Sagar D
– Sagar D, Commented Sep 1, 2014 at 8:25

ortis · Accepted Answer · 2014-09-01 08:46:48Z

1

One way is to hardcode the type check of classObj:

private void doOperation(final Object objClass)
{
    if(objClass instanceof ClassOne)
        doOperation((ClassOne)o);
    else if(objClass instanceof ClassTwo)
        doOperation((ClassTwo)o);
    else if(objClass instanceof ClassThree)
        doOperation((ClassThree)o);
    else if(objClass instanceof ClassFour)
        doOperation((ClassFour)o);
    else if(objClass instanceof ClassFive)
        doOperation((ClassFive)o);


}

Since you already hardcoded overloads of doOperation I guess this solution can fit your implementation.

Another way, is to use reflection to call the appropriate method:

public void startOperation(List<String> classNameList)
{
    for (String string : classNameList)
    {
        Class actualClass = Class.forName(className);
        Object classObj = actualClass.newInstance();
        Method doOperation = ClassImpl.class.getDeclaredMethod("doOperation", actualClass);
        doOperation.setAccessible(true);//doOperation is private, we need to bypass that
        doOperation.invoke(this, classObj); 
    }
}

edited Sep 1, 2014 at 8:46

answered Sep 1, 2014 at 8:41

ortis

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2 Comments

DCoder Over a year ago

Method doOperation = ClassImpl.class.getDeclaredMethod("doOperation", actualClass); at this point getting error NoSuchMethod found hence doOperation.setAccessible(true); is not getting executed

ortis Over a year ago

Are doOperation methods part of class ClassImpl ?

Sergey Kalinichenko · Accepted Answer · 2014-09-01 08:33:20Z

0

You can do it with reflection:

for (String string : classNameList) {
    Class actualClass = Class.forName(className);
    Object classObj = actualClass.newInstance();
    Method doOp = this.getClass().getDeclaredMethod("doOperation", actualClass);
    doOp.setAccessible(true);
    doOp.invoke(this, classObj);                            
}

answered Sep 1, 2014 at 8:33

Sergey Kalinichenko

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2 Comments

DCoder Over a year ago

it giving noSuchMethod exception

DCoder Over a year ago

i guess private method cannot be retrieved like this because I have checked using this.getClass().getMethods() which returned all public methods

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