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Java's type system does not support it and can only be implemented through plug-ins: Checker Framework, you need to add annotations and specify the plug-in during compilation.

The above implements the compiler's detection of null. As for the crash if null is passed, this can be achieved by inserting null check code through a plug-in.

Good question. I usually only focus on how to implement functions, but I haven’t thought much about why Java doesn’t implement them this way, such as this question. It also evoked a lot of wild imagination in me. It would be great if Java syntax was supported. The development efficiency would be at least several times higher. But when I think about it again, something seems wrong.

NullPointerException is a runtime exception for a certain reason

Assuming Java supports such syntax, use annotation: @NotNullIndicate that the parameter is not empty

A scenario like this: After the user successfully logs in, update the user's login time and IP.

User data includes:

Update user information pseudo code:

public void updateAccount(@NotNull Account account) {
    // 因?yàn)榭隙ú粸榭?，可以放心大膽的更新Account的最新登錄時間、ip
}

@NotNull表示參數(shù)：account means the parameter: account cannot be empty, there is no problem here.

Get user information to verify login pseudo code:

public Account login(String name) {
    // 1、連接數(shù)據(jù)庫
    // 2、根據(jù)用戶名獲取Account
    // 3、驗(yàn)證用戶信息
    // 4、驗(yàn)證成功返回Account信息，驗(yàn)證失敗返回null
}

We just make sure that the parameters cannot be empty, and we don’t want the return value to be empty, so there is no problem.

Main logic judgment pseudo code:

public static void main(String[] args) {
    AccountService service = new AccountService();
    // aaa登錄
    Account account = service.login("aaa","123456");
    service.updateAccount(account);
    
    // bbb登錄
    Account account = service.login("bbb","123456");
    service.updateAccount(account);
    
    // ccc登錄
    Account account = service.login("ccc","123456");
    service.updateAccount(account);
}

Then the question arises, whether the account parameter can be passed inservice.updateAccount()方法，編譯能不能通過？從數(shù)據(jù)庫中讀取的Accoount對象本來就是個模凌兩可對象，有可能代表某個人，也有可能是null.

Then make the return value non-null?

Yes, it can be like this. This becomes a pattern called NullObject Pattern , which means to create a dedicated empty object to represent that the result is empty.

Please check for details:

• https://segmentfault.com/q/10...

• http://www.cnblogs.com/haodaw...