在java主函数中使用swing泛型类

Question

我使用以下代码创建泛型类。这段代码主要用于在java中获取文本字段中的焦点。假设我们给tab或Shift-tab键，JTextField文本将被选中。我不知道如何在java程序中实现泛型类

import java.awt.FlowLayout;
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;
import javax.swing.JFrame;
import javax.swing.JTextField;
//import javax.swing.text.JTextComponent;


class MyFocusListener<T extends JTextField> extends FocusAdapter {

    public void focusGained(FocusEvent evt) {
        final T c = (T)evt.getSource();
        String s = c.getText();
        c.requestFocus();
        c.selectAll();

        for (int i = 0; i < s.length(); i++) {
            if (!Character.isDigit(s.charAt(i))) {
                c.setSelectionStart(i);
                c.setSelectionEnd(i);
                break;
            }
        }
    }

    public void focusLost(FocusEvent evt) {
        final T c = (T) evt.getSource();
        String s = c.getText();

        if (evt.isTemporary()) {
            return;
        }
        for (int i = 0; i < s.length(); i++) {
            if (!Character.isDigit(s.charAt(i))) {
            c.requestFocus();
                c.selectAll();
                break;
            }
        }
    }
}