检查所有JtextFields和Password后，如何使actionListener使用if / else语句执行操作

Question

    JButton btnSubmit = new JButton("Submit");
    btnSubmit.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            String  firstName = firstNameField.getText();\\gets user input
            String  surname =   surnameField.getText();\\gets user input
            String  username    =   usernameField.getText();\\gets user input
            char[] newPassword  =   password.getPassword();
            char[] confirmNew   =   confirmPassword.getPassword();

How do I make below conditional statement check if all fields are completed and displays the completion responses.

            if(firstName == null && surname ==null && username == null && newPassword == null && confirmNew ==  null){
                completionResponse.setText("All fields must be completed");
            }else
            completionResponse.setText("Congratulations! account have been successfully created");
        }

    });

Answer 1

Now you are checking if all fields == null, which is probably false (assuming at least something is filled in).

if(firstName == null || surname ==null || username == null || newPassword == null || confirmNew ==  null){
completionResponse.setText("All fields must be completed");
...