如何使用作为命令参数传输的 String 变量到 Java 中另一个类的实例？

Question

How can I use the String variable transferred as the command parameter to a instance of another class in Java?

Like this:

public class NBody {
    public static void main(double T, double dt, String filename) {
        In filename = new In();
        filename.readInt();
    }
}

It notified as:

NBody.java:3: filename is already defined in main(double,double,java.lang.String) In filename = new In();

Answer 1

What you are trying to do is define multiple variables which have the same name, so it is impossible. Imagine if it was possible, how would java runtime know which one you reference?

However if what you want is reference a variable which name's given as command line argument. You can use Reflection.

import java.lang.reflect.*;
public class Main {
    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {
        Field staticFieldMInt = Custom.class.getField("mInt"); // this can be argument
        Integer mInt = (Integer) staticFieldMInt.get(null); // null because it is a class property.
        System.out.println(mInt); // prints 10
    }
}

public class Custom {
    public static Integer mInt = 10; // this could be any type
}

Answer 2

You can't use runtime information (the content of a variable) to determine the name of a local variable. Variable names are a compile-time thing, not a runtime thing.