java - 自動生成ID

Question

顧客の ID を自動生成しようとしていますが、取得するのは毎回 0 だけです。

問題が にあることを確認してpublic void regCustomer()ください。

public class User {
private String firstName, gender, age;
String surename;
private int customerID;
private static int idCounter = 1000;
User next;

public User(String fN, String sn, String g, String a) {
    firstName = fN;
    surename = sn;
    gender = g;
    age = a;
    //customerID = cID;
    next = null;
}

public void setCustomerID() {
    customerID = idCounter++;
}

public int getCustomerID() {
    return customerID;
}

public String toString() {
    return customerID + "\t" + surename + "\t" + firstName + "\t" + age
            + "\t" + gender;

}

}

Windowクラスで

public void regCustomer() {


    //int customerID = 0;//= Integer.parseInt(customerIDField.getText());
    String firstName = firstNameField.getText();
    String surename = surenameField.getText();
    String gender = genderField.getText();
    String age = ageField.getText();

    if (!firstName.equals("") && !surename.equals("") && !gender.equals("")&& !age.equals("")) {
        userA.regCustomer(new User(firstName, surename, gender,age));
        User u = new User(firstName, surename, gender,age);
        u.getCustomerID();
        customerIDField.setText("");
        firstNameField.setText("");
        surenameField.setText("");
        ageField.setText("");
        genderField.setText("");
        firstNameField.requestFocus();
    } else
        JOptionPane.showMessageDialog(this, "Alle felt må fylles inn");
}