Why Exception in thread "main" java.lang.NoSuchMethodError: main?

Question

我查了一下好像是个常见的错误，但是根据我搜集到的信息，主要是main方法的行为不对造成的，而这里我什么也没检查。

import java.util.Scanner;

public class NBody {

    public static void main(double T, double dt, String filename) {

        In f = new In(filename);
        int N = f.readInt();
        double R = f.readDouble();

        Planet planets[] = new Planet[N]; 

        for (int i = 0; i < N; i++) {
            planets[i] = getPlanet(f);
        }

        StdDraw.setScale(-R, R);

        for (Planet star:planets) {
            star.draw();
        }
    /*
        for (Planet star:planets) {
            star.update(dt);
            StdDraw.picture(star.x, star.y, star.imgName);
        }
    */

    }

    public static Planet getPlanet(In file) {
        double x = file.readDouble();
        double y = file.readDouble();
        double xVelocity = file.readDouble();
        double yVelocity = file.readDouble();
        double mass = file.readDouble();
        String imgName = file.readString();
        Planet p = new Planet(x, y, xVelocity, yVelocity, mass, imgName);
        return p;
    }

}

那么我该如何解决这个问题呢？我没有向它传递任何参数，java NBody 就失败了（我编译成功，我可以保证）。

Answer 1

您的 main 方法签名错误。要成为 Java 应用程序的入口点，它必须有一个 String[] 类型的参数（和 void return 类型，并且它必须是 public 和静态):

public static void main(String[] args)

或

public static void main(String... args)

参数名称不重要。

您需要将命令行参数解析为适当的类型，例如

// TODO: Validation, e.g. that there are 3 command line arguments
// TODO: Use meaningful and conventional variable names
double T = Double.parseDouble(args[0]);
double dt = Double.parseDouble(args[1]);
String filename = args[2];

Answer 2

public static void main(String[] args)
{
double T = Double.parseDouble(args[0]);
double dt = Double.parseDouble(args[1]);
String filename = args[2];
}

如果您使用的是命令提示符

javac NBody.java

java NBody {1stparam} {1stparam} {1stparam}

javac NBody.java 
java NBody 12.2 12.3 filamename

Space这里是分隔符

12.2 will be placed to args[0] 
12.3 will be placed to args[1] and 
filename will be placed to args[2].

因为它是字符串，所以你将要做

  double value = Double.parseDouble(string);

Why Exception in thread "main" java.lang.NoSuchMethodError: main?

Why Exception in thread "main" java.lang.NoSuchMethodError: main?

java

nosuchmethoderror