java - 地址簿 - 错误

Question

我正在为一个类(class)开发一个地址簿程序，在我的代码中的某个地方我完全迷失了，似乎无法找出为什么我会遇到特定的错误。目前它由 3 个程序组成。 Menu.java、JGAddressBook.java 和 JursekGregChapter10t.java

import java.util.ArrayList;
import java.util.Scanner;

public class JursekGregChapter10t
{
   public static void main(String [] args)
   {
     Scanner s=new Scanner(System.in);
     System.out.println("Welcome to JGAddressBook");
     ArrayList<JGAddressBook> list = new ArrayList<JGAddressBook>();

     while(true)
     {
        display();
        int ch=s.nextInt();
           if(ch==0)
           {
              System.out.println("Please Enter First Name: ");
              String a=s.nextLine();

              System.out.println("Please Enter Last Name: ");
              String b=s.nextLine();

              System.out.println("Please Enter Street Address: ");
              String c=s.nextLine();

              System.out.println("Please Enter City, State: ");
              String d=s.nextLine();

              System.out.println("Please Enter Zip Code: ");
              String e=s.nextLine();

              JGAddressBook item =new JGAddressBook(a,b,c,d,e);
              list.add(item);
           }

           else if((ch==1)||(ch==2)||(ch==3)||(ch==4)||(ch==5))

           {  
                 System.out.println("Please enter value to search for: ");
                 String q=s.nextLine();
                 JGAddressBook temp=search(list,q,ch);

              if(temp==null)
              {
                 System.out.println("No Entry Found");
              }  

              else
              {
                 System.out.println("First Name: "+temp.FirstName);
                 System.out.println("Last Name: "+temp.LastName);
                 System.out.println("Street Address: "+temp.StreetAddress);
                 System.out.println("City,State: "+temp.CityState);
                 System.out.println("Zip Code: "+temp.ZipCode);
                 System.out.println();
              }

           }

           else if(ch==6)
           {

           break;

           }

           else
           {
              System.out.println("Error: Invalid input");
           }

      }
   }
}

这是第一个程序，第二个程序紧随其后，然后是第三个

 import java.io.*;

 import java.util.*;


class JGAddressBook  {

   String FirstName;
   String LastName;
   String StreetAddress;
   String CityState;
   String ZipCode;

   public JGAddressBook()

      {

      FirstName="";
      LastName="";
      StreetAddress="";
      CityState="";
      ZipCode="";

      }  

   public JGAddressBook(String a,String b,String c,String d,String e)

      {
      FirstName=a;
      LastName=b;
      StreetAddress=c;
      CityState=d;
      ZipCode=e;
      }

   public void addEntry(String a,String b,String c,String d,String e)

      {
      FirstName=a;
      LastName=b;
      StreetAddress=c;
      CityState=d;
      ZipCode=e;
   }
}

第三个...

import java.util.ArrayList;

public class Menu
  {

  public static void display()
     {
     System.out.println("Menu: Press the following");
     System.out.println("0. Add New Entry");
     System.out.println("1. Search First Name");
     System.out.println("2. Search Last Name");
     System.out.println("3. Search Street Address");
     System.out.println("4. Search City, State");
     System.out.println("5. Search Zip Code");
     System.out.println("6. Exit ");
     }

  public static JGAddressBook search(ArrayList A, String c, int field)
  {
     JGAddressBook item=new JGAddressBook();

     for (int i=0; i < A.size(); i++)
        {
        item=(JGAddressBook) A.get(i);

        if(field==1)
        {
           if(item.FirstName.equals(c))
           return item;
        }

        else if(field==2) 
        {
           if(item.LastName.equals(c))
           return item;
        }

        else if(field==3)
        {
           if(item.StreetAddress.equals(c))
           return item;
        }

        else if(field==4)
        {
           if(item.CityState.equals(c))
           return item;
        }

        else
        {
           if(item.ZipCode.equals(c))
           return item;
        }

     }

     return null;

  }
}

我在编译第一个程序时遇到的错误如下:

/Users/Greg/Documents/Programming/Java/JursekGregChapter10t.java:15: error: cannot find symbol
        display();
        ^
  symbol:   method display()
  location: class JursekGregChapter10t
/Users/Greg/Documents/Programming/Java/JursekGregChapter10t.java:43: error: cannot find symbol
                 JGAddressBook temp=search(list,q,ch);
                                    ^
  symbol:   method search(ArrayList<JGAddressBook>,String,int)
  location: class JursekGregChapter10t
2 errors
[Finished in 0.6s with exit code 1]

Answer 1

第一个错误，您需要在 Menu 对象上调用 static display() 方法，而不是尝试调用 display () 来自您的 JursekGregChapter10t 类:

Menu.display();

其次，您还调用 search(list,q,ch) ，而您应该在 Menu 对象上调用 search(...) :

Menu.search( list, q, ch );

编辑进一步的问题 - 当您使用 nextInt() 方法时，它不会消耗该行的其余部分。这意味着当系统提示您在界面中输入值时，该值将由 nextInt() 方法收集。然而，当您对名字使用 nextLine() 方法时，nextLine() 会消耗该行的其余部分，包括 \n。这意味着它会消耗您输入之前的所有内容(就在其之前)。因此，当为姓氏调用 nextLine() 时，它会消耗您的名字和姓氏(直到 \n)。

int ch=s.nextInt();

这是修复:

int ch=s.nextInt();
s.nextLine();