Invoking a method by reflection

Question

I took a look at that question You can pass methods as a parameter? and tried to invoke a method from one class, in another, passing as parameters the screen/class and the method name.

The purpose of doing this, is that in my application, I do several routines within a given method, which is triggered by an event (a ActionListener, for example) and every time I need to do something "different", I have to overwrite the event that triggers this method, put the new routine and sometimes even repeat others.

I believe that by doing so, I could have a greater possibility in doing some routines. I could have several different screens with the component MyField which does the same function, and on the screens I want a particular method to be executed together or after the methods of MyField, I would do it quietly, passing it as parameter.

Apparently, it seemed to me a coherent idea, but I could be mistaken, and in this case, I’m open to more efficient and "correct suggestions".

To illustrate better what I intend, I made a simple example.

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class TesteReflection extends JFrame {

    public static void main(String[] args) {
        Runnable startApp = () -> {
            TesteReflection tr = new TesteReflection();
        };
        SwingUtilities.invokeLater(startApp);
    }

    private MyField myField = new MyField();
    private JButton button = new JButton("Click !");

    public TesteReflection() {
        add(button);
        setSize(300, 200);
        setVisible(true);
        button();
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    private void button() {
        button.addActionListener(e -> {
            metodoA();
        });
    }

    private void metodoA() {
        MyField.actions(myField, TesteReflection.class, "metodoB");
    }

    private void metodoB() {
        System.out.println("Método B");
        //faz alguma coisa ..
    }
}

import java.lang.reflect.Method;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class MyField extends JPanel {

    private JTextField jTextField = new JTextField();

    public MyField() {
        actions();
    }

    private void actions() {
        jTextField.addActionListener(e -> {
            //faz alguma coisa ..
        });
    }

    public static void actions(MyField component, Class tela, String methodName) {
        component.getjTextField().addActionListener(e -> {
            try {
                //Method method = tela.getDeclaredMethod(methodName, new Class[]{});
                Method method = tela.getClass().getDeclaredMethod(methodName, String.class);
                method.setAccessible(true);
                method.invoke(tela);

                System.out.println("Chamei com sucesso o método " + methodName);
            } catch (Exception ev) {
                ev.printStackTrace();
            }
        });
    }

    public JTextField getjTextField() {
        return jTextField;
    }

}

Answer 1

Your Reflection fails because the metodoB is an instance method and not a static method. Therefore, to invoke it (either normally or by Reflection), you need the instance.

You even try to solve it using tela.getClass(). However, tela is the type Class, and so the result of that would be Class.class, which is definitely not what you want. Also, when specifying String.class as parameter, you will not find what you wanted, because the method you want is just metodoB() and not metodoB(String).

The code can be like this:

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class TesteReflection extends JFrame {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            new TesteReflection();
        });
    }

    private MyField myField = new MyField();
    private JButton button = new JButton("Click !");

    public TesteReflection() {
        add(button);
        setSize(300, 200);
        setVisible(true);
        button();
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    private void button() {
        button.addActionListener(e -> metodoA());
    }

    private void metodoA() {
        myField.actions(this, TesteReflection.class, "metodoB");
    }

    private void metodoB() {
        System.out.println("Método B");
        //faz alguma coisa ..
    }
}

import java.lang.reflect.Method;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class MyField extends JPanel {

    private JTextField jTextField = new JTextField();

    public MyField() {
    }

    public <E> void actions(E tela, Class<E> classe, String methodName) {
        jTextField.addActionListener(e -> {
            try {
                Method method = classe.getDeclaredMethod(methodName);
                method.setAccessible(true);
                method.invoke(tela);

                System.out.println("Chamei com sucesso o método " + methodName);
            } catch (Exception ev) {
                ev.printStackTrace();
            }
        });
    }
}

However, what you want would probably look better and easier with method References:

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class TesteReflection extends JFrame {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            new TesteReflection();
        });
    }

    private MyField myField = new MyField();
    private JButton button = new JButton("Click !");

    public TesteReflection() {
        add(button);
        setSize(300, 200);
        setVisible(true);
        button();
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    private void button() {
        button.addActionListener(e -> metodoA());
    }

    private void metodoA() {
        myField.actions(this::metodoB);
    }

    private void metodoB() {
        System.out.println("Método B");
        //faz alguma coisa ..
    }
}

import javax.swing.JPanel;
import javax.swing.JTextField;

public class MyField extends JPanel {

    private JTextField jTextField = new JTextField();

    public MyField() {
    }

    public void actions(Runnable r) {
        jTextField.addActionListener(e -> r.run());
    }
}