Whenever I chose any radioButton it automatically selects the last one, What should I do?

Below is a short snippet of my code used in my Swing Application, Its an mcq application where I've used radioButtons as the mean to select the chosen option, However when I try selecting any option from 1-4, It automatically selects the last one. Now I've tried putting the last button in the else if condition as well but I dont know what I should write in the else condition then.

JButton btnNext_1 = new JButton("Next");
btnNext_1.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
    /*  if(db_ans.equals(studentAnswer))
        {
            
            tmarks=tmarks+db_marks;
            System.out.println("correct-second");
            
        }*/ 
            
            buttonGroup.clearSelection();
                if(radioButton.isSelected())
                {
                    studentAnswer=radioButton.getText();
                    radioButton_1.setSelected(false);
                    radioButton_2.setSelected(false);
                    radioButton_3.setSelected(false);
                    System.out.println(studentAnswer);
                    
                }
                else if(radioButton_1.isSelected())
                {
                    studentAnswer=radioButton_1.getText();
                    System.out.println(studentAnswer);
                    radioButton.setSelected(false);
                    radioButton_2.setSelected(false);
                    radioButton_3.setSelected(false);
                    
                }
                else if(radioButton_2.isSelected())
                {
                    studentAnswer=radioButton_2.getText();
                    System.out.println(studentAnswer);
                radioButton.setSelected(false);
                radioButton_1.setSelected(false);
                radioButton_3.setSelected(false);
                }
                else if  {
                    studentAnswer=radioButton_3.getText();
                    System.out.println(studentAnswer);
                    radioButton.setSelected(false);
                    radioButton_1.setSelected(false);
                    radioButton_2.setSelected(false);
                }
                
                if(db_ans.equals(studentAnswer))
                {
                    
                    tmarks=tmarks+db_marks;
                    System.out.println("correct-second");
                }

});

As said in comments you would want to use a ButtonGroup this will allow only 1 JRadioButton to be selected at a time, see below for a simple example:

TestApp.java:

import java.awt.event.ActionEvent;
import javax.swing.BoxLayout;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.SwingUtilities;

public class TestApp {

    public TestApp() {
        initComponents();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(TestApp::new);
    }

    private void initComponents() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel();
        panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));

        JRadioButton option1 = new JRadioButton("Option 1");
        option1.setSelected(true);
        JRadioButton option2 = new JRadioButton("Option 2");

        ButtonGroup group = new ButtonGroup();
        group.add(option1);
        group.add(option2);

        panel.add(option1);
        panel.add(option2);

        JButton button = new JButton("What did I choose?");
        button.addActionListener((ActionEvent e) -> {
            if (option1.isSelected()) {
                JOptionPane.showMessageDialog(frame, "You chose option 1");
            } else if (option2.isSelected()) {
                JOptionPane.showMessageDialog(frame, "You chose option 2");
            }
        });
        panel.add(button);

        frame.add(panel);
        frame.pack();
        frame.setVisible(true);
    }

}

Essentially each JRadioButton is added to the same ButtonGroup and each JRadioButton is then added to the panel. Now you will only be able to select 1 option from within the same group, and there is no need to set any other JRadioButton in the same group to false.