java 自动生成id
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Auto generate id
提问by user2248471
I'm trying to auto generate an id for customers, and all i get is 0 every time.
我正在尝试为客户自动生成一个 id，每次我得到的都是 0。
Pretty sure the problem is in public void regCustomer().
很确定问题出在public void regCustomer().
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;
}
}
}
In the Windowclass
在Window班级
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 m? fylles inn");
}
回答by Boris the Spider
You never set the ID and that is why it is zero.
您从未设置过 ID，这就是它为零的原因。
You can use a private static final AtomicIntegerto generate your id sequence; simply read from it in your constructor:
您可以使用 aprivate static final AtomicInteger来生成您的 id 序列；只需在您的构造函数中读取它：
private static AtomicInteger ID_GENERATOR = new AtomicInteger(1000);
public User(String fN, String sn, String g, String a) {
customerID = ID_GENERATOR.getAndIncrement();
//rest of constructor
}
You should use an AtmoicIntegeras this is thread safe and the getAndIncrementmethod is atomic. There are not such guarantees for an int.
您应该使用 anAtmoicInteger因为这是线程安全的并且该getAndIncrement方法是原子的。没有这样的保证int。
The question that needs to answered is whether these items are persisted in any way, and if so what happens then - id generation will always start from 1000 using this technique.
需要回答的问题是这些项目是否以任何方式持久化，如果是，那么会发生什么 - 使用此技术生成 id 将始终从 1000 开始。
回答by drew moore
Move customerID = idCounter++;to the constructor.
移动customerID = idCounter++;到构造函数。
