ActionListener And Action Class Level Variable Swing Event

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import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;

public class JavaClasslevelActionListner extends JFrame {

	JTextField field = new JTextField();

	public static void main(String[] args) {
		JavaClasslevelActionListner listner = new JavaClasslevelActionListner();
	}

	public JavaClasslevelActionListner() {
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		JButton button = new JButton("Press me");
		button.addActionListener(new ButtonListener());
		this.getContentPane().setLayout(new BorderLayout());
		this.getContentPane().add(button, BorderLayout.SOUTH);
		this.getContentPane().add(field, BorderLayout.NORTH);
		this.pack();
		this.setVisible(true);
	}

	class ButtonListener implements ActionListener {
		boolean toggle = true;

		public void actionPerformed(ActionEvent e) {
			if (toggle)
				field.setText("JavaScan");
			else
				field.setText("Hello");
			toggle = !toggle;
		}
	}
}
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