Using the main() function in Java

The main() method usage in JAVA requires specific code examples

In JAVA, main() is a special method and is the entry point of the program. When the program starts, the JVM will start execution from the main() method, and the program will terminate only after the main() method is executed.

The main() method is defined as follows:

public static void main(String[] args) {
    // 程序代码
}

Among them, public is an access modifier, indicating that the method can be accessed by any class; static indicates that the method is static and can be directly accessed by Class call without instantiating the object; void means that the method has no return value; String[] args means that the method receives a string array as a parameter.

The following is a detailed description of the usage of the main() method and the corresponding code example:

1. Output Hello World!

   public static void main(String[] args) {
    System.out.println("Hello World!");
   }

   In the above In the code, a line of code System.out.println("Hello World!"); in the main() method is used to output the string "Hello World!" to the console.

2. Receive command line parameters and output

   public static void main(String[] args) {
    if(args.length > 0) {
        System.out.println("命令行参数为：" + args[0]);
    } else {
        System.out.println("没有输入命令行参数！");
    }
   }

   In the above code, the length of args is used to determine whether there are command line parameters passed in. If there is, the value of the command line parameter is output; if not, the prompt message is output.

3. Use a loop structure to output numbers from 1 to 10

   public static void main(String[] args) {
    for(int i = 1; i <= 10; i++) {
        System.out.println(i);
    }
   }

   In the above code, use a for loop structure to loop out each number from 1 to 10.

4. Call other methods

   public static void main(String[] args) {
    int result = sum(5, 3);
    System.out.println("两个数的和为：" + result);
   }
   
   public static int sum(int a, int b) {
    return a + b;
   }

   In the above code, the main method main() calls the sum() method and saves the sum of the two numbers as the return value into the result variable, and finally output the result.

Through the above examples, we can see that the main() method has various uses and can be used flexibly according to needs. It is not only the entrance to the program, but can also perform various operations and call other methods to implement more complex functions.

It should be noted that a JAVA program can have multiple classes, but there can only be one class containing the main() method. When running a program, the JVM will start execution from the specified class containing the main() method.

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