当您使用 java 命令从命令行运行 Java 应用程序时，例如，

When you use the java command to run a Java application from the command line, e.g.,

java some.AppName arg1 arg2 ...

该命令加载您指定的类，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:

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(final String[] args) {
        // body of main method follows
        ...
    }
}

入口点方法的具体要求是:

The specific requirements for the entry point method are:

1. 该方法必须在指定的类中.
2. 方法的名称必须是main"；正是那个大写¹.
3. 方法必须是public.
4. 方法必须是static ².
5. 方法的返回类型必须是void.
6. 该方法必须只有一个参数，并且参数的类型必须是 String[] ³.

1. The method must be in the nominated class.
2. The name of the method must be "main" with exactly that capitalization¹.
3. The method must be public.
4. The method must be static ².
5. The method's return type must be void.
6. The method must have exactly one argument and argument's type must be String[] ³.

(参数可以使用varargs语法声明；例如String... args.见这个问题 了解更多信息.String[] 参数用于从命令行传递参数，即使您的应用程序不接受命令行参数.)

(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.)

如果上述要求中的任何一个不满足，java 命令将失败并显示消息的某些变体:

If anyone 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

或者，如果您运行的是非常旧版本的 Java:

Or, if you are running an extremely old version of Java:

java.lang.NoSuchMethodError: main
Exception in thread "main"

如果您遇到此错误，请检查您是否有一个 main 方法并且它满足上面列出的所有六个要求.

If you encounter this error, check that you have a main method and that it satisfies all of the six requirements listed above.

^{1 - 一个真正晦涩的变体是当main"中的一个或多个字符出现时不是 LATIN-1 字符……而是一个 Unicode 字符，看起来像显示时对应的 LATIN-1 字符.
2 - 此处解释了为什么要求方法是静态的.
3 - String 必须对应于 java.lang.String 而不是一个名为 String 的自定义类隐藏它.}

^{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 - Here is an explanation of why the method is required to be static.
3 - String must correspond to java.lang.String and not to a custom class named String hiding it.}