Question

import java.util.Scanner;

public class data {

    public static int setoriginal() {   //prompt user to input 4 digit number
        int n = 0;
        int l = 0;

        do {
            Scanner input = new Scanner(System.in);

            System.out.println("Please enter a 4 digit number: ");
            n = input.nextInt();

            if (n >= 1000 && n <= 9999) {
                break;
            } else {
                System.err.
                    printf("You did not enter 4 digits\n");
            }

            l = l + 1;
        }
        while (l < 3);

        return n;
    }           //end method

    public static int encrypt(int n) {  //encrypt number inputted by user

        int e1 = (((n / 1000) + 7) / 10);
        int e2 = ((((n % 1000) / 100) + 7) / 10);
        int e3 = ((((n % 100) / 10) + 7) / 10);
        int e4 = ((((n % 10) / 1) + 7) / 10);

        int e = e1 * 1000 + e2 * 100 + e3 * 10 + e4;

        int firstPart = e % 100;
        int lastPart = e / 100;

        int result = firstPart * 100 + lastPart;

        return result;
    }           //end method

    public static int decrypt(int result) { //decrypt encrypted number

        int d1 = (((result / 1000) - 7) * 10);
        int d2 = ((((result % 1000) / 100) - 7) * 10);
        int d3 = ((((result % 100) / 10) - 7) * 10);
        int d4 = ((((result % 10) / 1) - 7) * 10);

        int d = d1 * 1000 + d2 * 100 + d3 * 10 + d4;

        int firstPart1 = d % 100;
        int lastPart1 = d / 100;

        int result1 = firstPart1 * 100 + lastPart1;

        return result1;
    }           //end method

    public static int decrypt1(int n) { //decrypted number inputted by user

        int dd1 = (((n / 1000) - 7) * 10);
        int dd2 = ((((n % 1000) / 100) - 7) * 10);
        int dd3 = ((((n % 100) / 10) - 7) * 10);
        int dd4 = ((((n % 10) / 1) - 7) * 10);

        int dd = dd1 * 1000 + dd2 * 100 + dd3 * 10 + dd4;

        int firstPart1 = dd % 100;
        int lastPart1 = dd / 100;

        int result1 = firstPart1 * 100 + lastPart1;

        return result1;
    }           //end method

    public static void display(int n, int result, int result1) {    //output results
        System.out.println("Originl number is: " + n);
        System.out.println("\nEcrypted numebr is: " + result);
    }           //end method

    public static void display1(int n, int result, int result1) {   //output results
        System.out.println("Originl number is: " + n);
        System.out.println("\nDecrypted numebr is: " + result1);
    }           //end method

    public static void getOriginal(int n) { //return original number
        System.out.println("The original number is: \n" + n);
    }           //end method

    public static void getEncrypt(int n, int result) {  //return encrypted number
        System.out.println("The encrypted number is: \n" + result);
    }           //end method

    public static void main(String[]args, int result, int n, int result1) {
        int m = 0;
        Scanner input1 = new Scanner(System.in);

        System.out.print("\nPlease choose from the following menu ");
        System.out.print("\n1. Enter an original number");
        System.out.print("\n2. Encrypt the number and print it");
        System.out.print("\n3. Decrypt a number and print it");
        System.out.print("\n4. Quit\n");
        m = input1.nextInt();

        while (m < 1 || m > 4) {
            System.out.print("Error choose a number from 1-4");
            m = input1.nextInt();
        }

        if (m == 1) {
            setoriginal();
            main(args, m, m, m);
        }

        else if (m == 2) {
            if (setoriginal() == 0) {
                System.out.
                    print
                    ("Please enter an original number first");
                main(args, m, m, m);
            } else {
                encrypt(n);
                display(n, result, result1);
                main(args, n, result, result1);
            }
        } else if (m == 3) {
            if (encrypt(n) < 0) {
                System.out.
                    print("Please encrypt your number  first");
                main(args, n, result, result1);
            } else {
                decrypt(n);
                display1(n, result, result1);
                main(args, n, result, result1);
            }
        } else if (m == 4) {
            System.exit(0);

        }

    }
}

我在eclipse中没有编译错误，但是我收到一条错误，指出“选择不包含主类型”。什么想法可能是错的？如果您发现任何其他错误，请告诉我。

Answer 1

您应该使用：

public static void main(String[] args)

而不是：

public static void main(String[] args, int result, int n, int result1)

Answer 2

public static void main(String[]args, int result, int n, int result1) {

你需要学习做Java编程的一件事就是咒语：

public static void main(String args[]) {

正是这样（嗯，String[] args也起作用 - 并且名称无关紧要）JVM在查找运行程序的入口点时搜索的咒语。

<强>更新

如果您想从main()函数中获取任何参数，它们将被编码为String数组中的args[]个对象。只需索引它们：

$ cat Echo.java ; javac Echo.java ; java Echo Hello Cruel World
import java.lang.System;

class Echo {
    public static void main(String args[]) {
        for(int i=0; i<args.length; i++) {
            System.out.println(args[i]);
        }
    }
}
Hello
Cruel
World
$

当然，它们是String个对象。如果需要将它们转换为其他对象类，则必须正确解析字符串。（Integer()和类似的事情对于简单的案例可以派上用场。）

Answer 3

为了运行程序，java需要能够找到具有以下签名的方法：

public static void main(String[])

由于它无法在程序中找到它，因此无法开始执行，因此无法编译它。

要获得所需的效果，请将main方法的签名更改为上述方法，并根据String []的索引访问参数，如下所示：

result = Integer.parseInt( args[0] );
n = Integer.parseInt( args[1] );
result1 = Integer.parseInt( args[2] );

如果你将它添加到主方法的开头，你应该没问题。：d

为什么我在Eclipse中得到“Selection不包含主类型”消息？

3 个答案: