java - 这有什么问题吗？我找不到符号

Question

这是一个类的代码方法的前四行:

这是在“CrudController”类中

public String create(Object entity, Class clazz, String req_id, HttpServletResponse response) throws NullPointerException {
    if (entity == null ) throw NullPointerException("ENTITY");
    else if(clazz == null) throw NullPointerException("CLAZZ");
            else if(response == null) throw NullPointerException("RESPONSE");

我收到以下三行的错误:

[ERROR] /path/to/CrudController.java:[42,29] error: cannot find symbol
[ERROR]  class CrudController
[ERROR] /path/to/CrudController.java:[43,31] error: cannot find symbol
[ERROR]  class CrudController
[ERROR]/pathto/CrudController.java:[44,48] error: cannot find symbol
[ERROR]  class CrudController

位置编号(29、31 和 48 在“==”开头是正确的

Answer 1

将所有 throw NullPointerException(STRING); 更改为 throw new NullPointerException(STRING);

在这里你抛出了异常。异常是相应异常类型类的实例，因此您需要抛出一个实例，说明为什么需要 new 关键字。

public String create(Object entity, Class clazz, String req_id, HttpServletResponse     response) throws NullPointerException {
if (entity == null ) throw new NullPointerException("ENTITY");
else if(clazz == null) throw new NullPointerException("CLAZZ");
        else if(response == null) throw new NullPointerException("RESPONSE");