JAVA 编写时关于SCANNER的问题

Posted 2023-05-13

import java.util.Scanner;
public class gameDriver

public static Scanner scan = new Scanner(System.in);
public static Group g[] = new Group[2];
private static int menuChoice;
private static int groupChoice;

public gameDriver()

menuChoice = -1;
groupChoice = -1;



public static void menu()

System.out.print("<-- System Menu -->\n1. Add teams to group\n2. Input match result\n3. Display group ladders\n4. Display final standings\n5. Quit\n\nWhat do you want to do?: ");
menuChoice = scan.nextInt();

if(menuChoice==1)

setGroup();

else if(menuChoice==2)



else if(menuChoice==3)



else if(menuChoice==4)



else if(menuChoice==5)



else






public static void setGroup()

String teamName = new String();
String teamLocation = new String();

System.out.print("\nDo you want to add the teams to group 1 or 2: ");
groupChoice = scan.nextInt();

g[groupChoice-1]= new Group(groupChoice);

for(int i = 0; i<=3;i++)

System.out.print("\n\nAdding a team.\nWhat is the name of the team: ");
teamName = scan.nextLine();
System.out.print("\nWhere is the team from: ");
teamLocation = scan.nextLine();

g[groupChoice].t[i]= new Team(teamLocation,teamName);



System.out.print("\n\nGroup "+groupChoice+" is now full.");



public static void main(String[] args)


menu();



这一段程序我没写完，另外还有一个TEAM CLASS和一个GROUP CLASS可正常运行，问题是这段程序在运行到

for(int i = 0; i<=3;i++)

System.out.print("\n\nAdding a team.\nWhat is the name of the team: ");
teamName = scan.nextLine();
System.out.print("\nWhere is the team from: ");
teamLocation = scan.nextLine();

g[groupChoice].t[i]= new Team(teamLocation,teamName);


这段的时候What is the name of the team:
和Where is the team from:会紧接着出现，而不是等SCAN完了一个NAME滞后再SCAN LOCATION，然后就会出现RUNTIME ERROR应该是因为尝试把一个数值SCAN到两个变量里去……

请问为什么会这样……
yicaifenchen 写的运行是可以运行了，问题是我在那两个连着的SCAN那里必须要用到NEXTLINE而不是NEXT，因为输入中间要允许用空格之类的，我要扫描的是一整行……

参考技术A public static void setGroup()

String teamName = new String();
String teamLocation = new String();

这是什么？ 不是数组 也不是list 也不是变量

(我是菜鸟) 参考技术B import java.security.acl.Group;
import java.util.Scanner;

public class gameDriver

public static Scanner scan = new Scanner(System.in);
public static Group g[] = new Group[2];
private static int menuChoice;
private static int groupChoice;

public gameDriver()

menuChoice = -1;
groupChoice = -1;



public static void menu()

System.out.print("<-- System Menu -->\n1. Add teams to group\n2. Input match result\n3. Display group ladders\n4. Display final standings\n5. Quit\n\nWhat do you want to do?: ");
menuChoice = scan.nextInt();

if(menuChoice==1)

setGroup();

else if(menuChoice==2)



else if(menuChoice==3)



else if(menuChoice==4)



else if(menuChoice==5)



else






public static void setGroup()

String teamName = new String();
String teamLocation = new String();

System.out.print("\nDo you want to add the teams to group 1 or 2: ");
groupChoice = scan.nextInt(); ///scan use good

//g[groupChoice-1]= new Group(groupChoice);

for(int i = 0; i<=3;i++)

System.out.print("\n\nAdding a team.\nWhat is the name of the team: ");
//teamName = scan.nextLine();
teamName = scan.next();
System.out.print("\nWhere is the team from: ");
//teamLocation = scan.nextLine();
teamLocation = scan.next();
//g[groupChoice].t[i]= new Team(teamLocation,teamName);



System.out.print("\n\nGroup "+groupChoice+" is now full.");



public static void main(String[] args)


menu();


本回答被提问者采纳

Java 代码在 Scanner hasNextLine 处挂起

【中文标题】Java 代码在 Scanner hasNextLine 处挂起

【英文标题】：Java code hangs at Scanner hasNextLine

【发布时间】：2015-07-24 18:52:02

【问题描述】：

首先，我是 Java 新手，正在尝试完成学校关于创建自动售货机的作业。我的程序接收 2 个文件作为 cli 参数，一个用于产品，另一个用于金钱。

对于我的一生，我无法弄清楚为什么代码挂在第 42 行

 (while (moneyTemp.hasNextLine());)

我尝试使用断点在 Eclipse 上进行调试，并注意到代码从未超过这一行。在while循环中放置一个打印语句，我没有得到输出，所以我知道它没有循环。

java 文档说 hasNextLine 可以阻止等待用户输入，但由于我的源是一个文件，我不确定为什么会这样。请参阅下面的相关代码。

import java.util.Scanner;
import java.io.File;
import java.io.FileNotFoundException;

public class VendingMachine

    static Scanner input = new Scanner (System.in);

    public static void main(String[] args) 
    
        try
        
            Scanner productTempFile = new Scanner(new File(args[0]));
            Scanner moneyTemp = new Scanner(new File(args[1]));
            int numProducts = 0; //Number of products to be loaded to the machines
            int numMoney = 0;   //Number of money objects to be loaded in the machine

            while (productTempFile.hasNextLine()) //This block will get the number of products
            
                numProducts++;
                productTempFile.nextLine();
            
            productTempFile.close();


            Product[] invArray = new Product[numProducts];
            Scanner myFile = new Scanner(new File(args[0]));

            for(int i = 0; i < numProducts; i++)  //This block populates the array of products
            
                String inputLine = myFile.nextLine();                               
                String[] lineArray = inputLine.split(",");

                invArray[i] = new Product(lineArray[0], Double.valueOf(lineArray[1]), lineArray[2], lineArray[3],
                        Double.valueOf(lineArray[4]), Integer.valueOf(lineArray[5]));
             

            myFile.close();

            System.out.println("I'm here");

            while (moneyTemp.hasNextLine()); //This block gets the number of different money items
            
                numMoney++;
                moneyTemp.nextLine();               
            

下面是我提供的第二个文件，即 arg[1]，其格式与第一个文件相同。

PaperCurrency,100 Dollar Bill,100.0,medium,paper,0 PaperCurrency,50 Dollar Bill,50.0,medium,paper,0 PaperCurrency,20 Dollar Bill,20.0,medium,paper,0 PaperCurrency,10 Dollar Bill,10.0,medium,paper,4 PaperCurrency,5 Dollar Bill,5.0,medium,paper,8 PaperCurrency,1 Dollar Bill,100.0,medium,paper,16 CoinCurrency，50 美分，0.5，大，金属，10 CoinCurrency,Quarter,0.25,medium,metal,20 CoinCurrency,Dime,0.1,small,metal,30 CoinCurrency,Nickel,0.05,small,metal,40 CoinCurrency,Penny,0.01,small,metal,50

任何帮助将不胜感激。 谢谢

【参考方案1】：

从行中删除分号

 while (moneyTemp.hasNextLine());

分号使while循环完成其主体而不做任何事情意味着它就像while()当while条件为真时什么都不做，因为你的条件是hasNextLine()它一次又一次地检查同一行导致无限循环。

【讨论】：

啊，老分号在一段时间的末尾...我以前对此感到沮丧。

感谢您的快速回复。我不敢相信它这么小 :) 我在想它会是这么先进的东西。谢谢一百万。

【参考方案2】：

通过添加分号 (;)，您隐含地让 while 循环执行一个空块。 hasNextLine() 不会改变扫描器所基于的InputStream，所以由于while 循环的主体中没有任何内容，因此没有任何东西可以改变状态，并且循环将永远继续。

只需从while 循环中删除分号，就可以了：

while (moneyTemp.hasNextLine()) // no ; here!

    numMoney++;
    moneyTemp.nextLine();               

【讨论】：

这个答案与另一个答案有何不同？