制作除字符串以外的主要接受对象？

Question

Is it possible to have the main method accept an argument other than a string array? For example, can we have a method like main(Animals[]args){/*code*/} ? If not, then why?

Answer 1

No - the entry point is always the method with the header public static void main(String[] args) (ie the JVM invokes this particular method). You can certainly define a method

public static void main(Animals[] args) {...}

but it would not be executed directly upon running the program.

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EDIT : The reason the main method specifically has a string-array argument is because this array will contain the command-line arguments when the program is run. Intuitively, these should be strings (and certainly not Animal s, for example).

Answer 2

Because when you input from the command line you are entering strings, not a complex type.

So it makes sense for the argument to be an array of pointers (references) to strings, including or not (depending on the language) the count of the arguments. In Java this isn't needed as you can just use length .

Not sure why you'd want that?..

Answer 3

规范说它只能处理字符串数组。

Answer 4

There is nothing stopping you from having a public static void main that takes a parameter type other than String. The problem is the that the JVM needs simple rules for identifying and calling the method. It has an array of strings, eg from the command line, available to pass to the program. How would the JVM go about turning it into an array of Animal, or some other type, before it has started running your program?

Here's an example of a main that takes a different parameter type, and of the program itself dealing with producing the Animal array from the array of strings that the JVM has. Of course, it would really be better to give the second main method a more meaningful name.

  import java.util.Arrays;

  public class Bad {

    public static void main(String[] args) {
      Animal[] animals = new Animal[args.length];
      for (int i = 0; i < args.length; i++) {
        animals[i] = new Animal(args[i]);
      }
      main(animals);
    }

    public static void main(Animal[] args) {
      System.out.println(Arrays.asList(args));
    }

  }

  class Animal {
    String species;

    public Animal(String species) {
      this.species = species;
    }

    public String toString() {
      return "Animal: " + species;
    }
  }