检查属性是否具有属性(Check if property has attribute)

 当您使用java命令从命令行运行Java应用程序时，例如， 
 
    java some.AppName arg1 arg2 ...
 
 该命令加载您提名的类，然后查找名为main的入口点方法。 更具体地说，它正在寻找一个声明如下的方法： 
 
package some;
public class AppName {
    ...
    public static void main(String[] args) {
        // body of main method follows
        ...
    }
}
 
 入门点方法的具体要求是： 
 
 
 
 该方法必须在提名类中。 
 
 
 该方法的名称必须是正确的大写字母“main” 1 。 
 
 
 该方法必须是public 。 
 
 
 该方法必须是static 2 。 
 
 
 该方法的返回类型必须为void 。 
 
 
 该方法必须只有一个参数，参数的类型必须为String[] 3 。 
 
 
 参数可以使用varargs语法声明; 例如String... args 。 请参阅https://stackoverflow.com/a/36803396/139985 。 String[]参数用于从命令行传递参数，并且即使您的应用程序不使用命令行参数也是必需的。 
 
 如果上述要求中的任何一个不满足，则java命令将失败并显示以下消息： 
 
java.lang.NoSuchMethodError: main Exception in thread “main”
 
 如果遇到此错误，请检查您是否具有main方法，并满足上述所有6项要求。 
 
 
 1 - 一个真正模糊的变化是当“主”中的一个或多个字符不是LATIN-1字符，但是在显示时看起来像相应的LATIN-1字符的Unicode字符。 
 
 2 - 看看为什么Java的main方法是静态的？ 解释为什么该方法需要静态。 
 
 3 - String必须对应于java.lang.String而不是名为String的自定义类隐藏它。 

When you use the java command to run a Java application from the command line, e.g.,
 
java some.AppName arg1 arg2 ...
 
the command loads the class that you nominated, and then looks for the entry point method called main. More specifically, it is looking for a method that is declared as follows:
 
package some;
public class AppName {
    ...
    public static void main(String[] args) {
        // body of main method follows
        ...
    }
}
 
The specific requirements for the entry point method are:
 
 
 
The method must be in the nominated class.
 
 
The name of the method must be "main" with exactly that capitalization1.
 
 
The method must be public.
 
 
The method must be static 2.
 
 
The method's return type must be void.
 
 
The method must have exactly one argument and argument's type must be String[] 3. 
 
 
(The argument may be declared using varargs syntax; e.g. String... args. See this question for more information. The String[] argument is used to pass the arguments from the command line, and is required even if your application takes no command line arguments.)
 
If any one of the above requirements is not satisfied, the java command will fail with some variant of the message:
 
Error: Main method not found in class MyClass, please define the main method as:
   public static void main(String[] args)
or a JavaFX application class must extend javafx.application.Application
 
Or, if you are running an extremely old version of Java:
 
java.lang.NoSuchMethodError: main
Exception in thread "main"
 
If you encounter this error, check that you have a main method and that it satisfies all 6 of the requirements listed above.
 
 
1 - One really obscure variation of this is when one or more of the characters in "main" is NOT a LATIN-1 character ... but a Unicode character that looks like the corresponding LATIN-1 character when displayed.
 
2 - See Why is the Java main method static? for explanation of why the method is required to be static.
 
3 - String must correspond to java.lang.String and not a custom class named String hiding it.