I am new to java and JSP, i have doubt about accessing the method of tag class. i have created 3 custom tags namely Primary, Secondary, Axis. so i can access
<pre:Primary>
<pre:Axis/>
</pre:Primary>
<pre:Secondary>
<Pre:Axis/>
</pre:Secondary>
In Axis Tag class i have to access the parent methods, in this case primary, secondary is parent for Axis tag. In both parent class, i have method addItem(), i am calling the method as below in axis class.
Object parent=null;
try{
parent = (PrimaryWrapper)getParent();
}catch(Exception e){
parent = (SecondaryWrapper)getParent();
}
parent.addItem(axisItem);
but this is shows error, "The method addItem(StringBuilder) is undefined for the type Object", i know in try, catch only the scope of parent is changing to primary/secondary, hence the error occurs. but i have to access the appropriate addItem method based on Primary, Secondary. is it Possible? Or i am doing wrong.
Thanks in advance
The problem is the parent variable is of class Object, so anything you assign to it, you can only use the Object's methods. I see basically two possible solutions.
Quick and dirty
Object parent = getParent();
if (parent instanceof PrimaryWrapper) {
((PrimaryWrapper) parent).addItem(axisItem);
} else if (parent instanceof SecondaryWrapper) {
((SecondaryWrapper) parent).addItem(axisItem);
} else {
// log error?
}
Better - using Interface
// define an interface
public interface ItemContainer {
void addItem(StringBuilder item);
}
// change your Wrappers to implement the interface, i.e.
public class PrimaryWrapper extends ... implements ItemContainer {
// ... your code, just add @Override annotation to the addItem(...) method
}
// and
public class SecondaryWrapper extends ... implements ItemContainer {
// ... your code, just add @Override annotation to the addItem(...) method
}
// and finally, fix the AxisTag code
ItemContainer parent = (ItemContainer) getParent();
parent.addItem(axisItem);
Or, as mentioned in comment from Hacketo, instead of creating and interface, you could create an common ancestor class (e.g. Wrapper) and implement the common methods there. The code of AxisTag would be similar to the above solution with interface.
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