Why main method is public static void?

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mainThe first method is a method to know when we learn the Java programming language, have you ever wondered why mainthe method is public、static、voidof. Of course, many people first learn that C and C ++, but some subtle differences with the former, it will not return any value in Java main method, why mainapproach public、static、void, this article attempts to find some answers.

mianThe method is the entry Java program, remember that we are not here to discuss Servlet, MIDlet and any other java application container management, the core java programming, JVM looks for class public static void main (String [] args), If you can not find the method throws an error NoSuchMethodError: main program terminates.

mainMethods must strictly follow its grammatical rules, the method signature must be public static voidthe parameter is a string array type, if it is Java1.5 and later can use variable parameters:

public static void main(String... args)

1. Why main method is static (static)

• Because the main method is static, JVM calls this method does not need to create any instance that contains the main method.

• Because the C and C ++ the same as the main method similar entry program execution.

• If the main method is not declared as static, JVM must create an instance of the main class, as the constructor can be overloaded, JVM would not be able to determine which main method calls.

• Static methods and static data loaded into memory can be called directly without the need to create the same methods as instance after instance to call, if the main method is static, then it will be loaded into the JVM context methods become enforceable.

2, why the main method is public (public)

Java specifies the number of modifiers can be accessed, such as: private, protected, public, any method or variable can be declared as public, Java can be accessed from places outside the class. Because the main method is public, JVM can easily access execute it.

3, why the main method does not return a value (Void)

Because the main return any value to the program did not make any sense, it is designed to be void, meaning there will be no main value is returned.

4, summary

• mainThe method must be declared public、static、void, otherwise JVM can not run the program

• If you can not find the JVM mainmethod throws NoSuchMethodError: main exceptions, such as: If you run the command: java HelloWrold, JVM will search HelloWorld.class file public static void main (String[] args)method.

• mainThe entrance is a program, at the beginning of program execution.

• mainThe method is a specific thread "main" run, the program will run until the end of the main thread or non-daemon thread terminates.

• When you see "Exception in Thread main" such as: Excpetion in Thread main: Java.lang.NullPointedException, it means an exception from the main thread.

• You can declare maina method using a variable parameter java1.5 of ways, such as:
  public static void main(String... args)

• In addition static、void、和public, you can use final, synchronizedand strictfpmodifiers in the mainsignature method, such as:
  public strictfp final synchronized static void main(String[] args)

• mainLike other methods it can be overloaded methods in Java, but the JVM will call the above signature of this standard main method.

• You can use the throwsclause in the method signature, you can throw any checked and unchecked exceptions.

• JVM static initialization block call mainis executed before the method, they are loaded into memory when the JVM in the class was executed.