java 我可以在声明变量后将其设为 final 吗？
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Can I make a variable final after it has been declared?
提问by Matt
I'm making a banking model, and an Account class has an accountNumber field. The account number should never change, but I cannot set the field as final because this will prevent the constructor from setting it.
我正在制作一个银行模型，一个 Account 类有一个 accountNumber 字段。帐号不应更改，但我不能将该字段设置为 final，因为这将阻止构造函数设置它。
If it's not possible to do this, it doesn't matter. It's just for a CS assignment so I want to make sure I'm doing it the best way I can.
如果无法做到这一点，也没关系。这只是一个 CS 任务，所以我想确保我以最好的方式做这件事。
Would the best implementation be to just make the field and its setter method private?
最好的实现是将字段及其设置方法设为私有吗？
回答by mikej
The constructor canset it if it is marked as finale.g. the following is legal:
如果标记为例如以下是合法的，则构造函数可以设置它final：
public class BankAccount {
private final int accountNumber;
public BankAccount(int accountNumber) {
this.accountNumber = accountNumber;
}
}
In fact if a field is marked as finalbut not initialised in its declaration then it must be set in all constructors.
事实上，如果一个字段final在其声明中被标记为但未初始化，那么它必须在所有构造函数中设置。
If you do not put a public setter on the class then the account number can't be changed from outside the class but marking it as final will also prevent it (accidentally) being changed by any methods inside the class.
如果您没有在类上放置公共设置器，则无法从类外部更改帐号，但将其标记为 final 也将防止它（意外地）被类内的任何方法更改。
回答by Pablo Fernandez
If a variable is finalit can (and must) be initialized in the constructor.
如果一个变量是final它可以（并且必须）在构造函数中初始化。
