java中的public static void main（String arg []）是固定的吗？ [英] public static void main(String arg[ ] ) in java is it fixed?

问题描述

我最近在考试中被问到 public static void main（String arg []）格式 main 方法是固定的？
我们可以改变吗？
我们可以使用 main 而不使用任何 public ， static 或 void ？
如果没有，为什么不硬编码 main（String arg []）代表 public static void main（String arg []）总是？

I was recently asked in an exam if public static void main(String arg[]) format of main method was fixed? Can we change it? Can we use main without any of public, static or void? If not, why is it not hard coded that main(String arg[]) would stand for public static void main(String arg[]) always?

推荐答案

主方法的签名在 Java语言规范部分12.1.4 并明确说明：

The signature of the main method is specified in the Java Language Specifications section 12.1.4 and clearly states:

方法main必须声明为public，static和void。必须
指定一个形式参数（§8.4.1），其声明的类型是
String的数组。

The method main must be declared public, static, and void. It must specify a formal parameter (§8.4.1) whose declared type is array of String.

• 它必须是 public 否则无法调用它


• 它必须 static 因为在调用之前无法实例化对象


• String arguments允许在从命令行执行Java程序时传递参数。可以在没有参数的情况下定义它，但是更实用（和其他语言类似）


• 返回类型是 void 因为没有其他任何东西是没有意义的：Java程序可以在到达main方法结束之前终止（例如，通过调用 System.exit（））


• it must be public otherwise it would not be possible to call it
• it must be static since you have no way to instantiate an object before calling it
• the list of String arguments is there to allow to pass parameters when executing a Java program from the command line. It would have been possible to define it without arguments but is more practical like that (and similar to other languages)
• the return type is void since it does not make sense to have anything else: a Java program can terminate before reaching the end of the main method (e.g., by calling System.exit())

方法签名因此可以是：

public static void main( String[] args )
public static void main( String... args )

请注意 varargs 版本（ ... ）仅在Java 5中有效

note that the varargs version (...) is only valid from Java 5

由于Java语言允许括号 [] 位于类型或变量之后（第一个通常是首选），

As the Java language allows the brackets [] to be positioned after the type or the variable (the first is generally preferred),

public static void main( String args[] ) // valid but usually non recommended

也有效

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