java如何在方法调用中传递数据和使用用户输入

Question

我最难理解使用外部变量的方法调用。以下是我在打印表单中尝试做的事情，下面我将粘贴两次尝试。当我试图修复我正在做的事情时，我不断收到相同错误消息的循环。我还希望用户输入一个数字来选择一个选项，我需要在其他地方使用它。这一切基本上都可以很容易地完成，但我正在努力练习来回传递论点

附件是一个picture详细说明了我正在尝试做什么，下面是代码

import java.util.Scanner;

public class SandwichShop {
    private String MOTTO = "Come back for another!";
    private int rye = 150;
    private int white = 120;
    public int decision;

    public void breadCals (int r, int w) {
        int sel;
        r = rye;
        w = white;
        if (sel == 1) {
            System.out.println("you entered 1 " + r);
        } else {
            System.out.println("you entered 2 ");
        }
    }  

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("Please enter ");
        int decision = input.nextInt();

        SandwichShop.decision();
    }
}

或者

import java.util.Scanner;

public class TestSandwich {
    private int calsR;
    private int calsW;
    private int ryeB;
    private int whiteB;
    private int decision = 0;
    private int selection;
    private String MOTTO = "Come back for another!";

    public static void main(String [] args) {
        breadType();
        //TestSandwich decision = new TestSandwich();
        //decision.Display();
     }

     public static int breadType() {
         int ryeB = 1;
         int whiteB = 2;
         Scanner input = new Scanner(System.in);
         //System.out.println("What type of bread do you want?");
         //System.out.println("Please enter 1 for Rye and 2 for White");
         int decision = input.nextInt();
         return decision;
     }

     public void bCals(){
         int calsR = 150;
         int calsW = 120;
     }

     public void Display(int decision) {
         int selection = decision;
         System.out.println("What type of bread do you want?");
         System.out.println("Please enter 1 for Rye and 2 for White");
         if (selection == 1) {
             System.out.println("Rye bread has " + calsR + " calories.");
         } else {
             System.out.println("White bread has " + calsW + " calories."); 
         }
         //System.out.println(MOTTO);
     }

     //!main - btype - display -bcals 

     /*

     public static int calsAmt( int cals) {

         TestSandwich.display();


     }*/
}

Answer 1

下面是对第一段代码的快速修改，这样您可能会理解得更多一些。我试着保留你的大部分代码

public class FirstClass {
public static int decision;     
public static void main(String[] args) { 

Scanner input = new Scanner(System.in);
System.out.println("Please enter ");
decision = input.nextInt();

System.out.println(decision);

SecondClass.breadCals();    //gets the method 
}}

二等舱

Public class SecondClass{

private static int rye = 150;
private static int white = 120; //static for a call like that
public int decision;

 public static  void breadCals () { 
   //method needs to be static to call it like i did
  int sel=FirstClass.decision;
  int  r = rye;
  int  w = white;
  if (sel == 1) System.out.println("you entered 1 " + r);
  else if(sel== 2) System.out.println("you entered 2 "+ w);
  else System.out.println("Wrong number"); 

    }
}