Question

I am using refection to get the declared fields of a class. Now I need to select only those which are UI components, for example JLabel, JFrame, etc. Is there a way to be able to determine whether a particular type extends java.awt.Compoenent?

I did manage to get the generic type of the field, however what i need is to be able to determine whether the field extends component

Answer 1

I’ve written an example of how to do this.
Find below the class being investigated:

import javax.swing.JLabel;
import javax.swing.JTable;
import javax.swing.JWindow;

public class Foo {
   int i;
   long j;
   String s;
   JTable table;
   JLabel label;
   JWindow window;
 }

And here is the code that checks the fields of this class:

import java.lang.reflect.Field;

public class Test {
   public static void main(String[] args) {
      new Test().run();
}

private void run() {
   Class<?> c = Foo.class;
   System.out.println("The following fields extend Component: ");
   for (Field f : c.getDeclaredFields()) {
      Class<?> fieldClass = f.getType();
      Class<java.awt.Component> compClass = java.awt.Component.class;      
      if (compClass.isAssignableFrom(fieldClass)) {
         System.out.println(f.getName());
      }
   }
 }
}

Output:

The following fields extend Component: 
table
label
window