java - java eclipse中的NoSuchElementException问题

Question

我使用Java eclipse，它显示有:

java.util.NoSuchElementException.

谁能帮我解决这个问题吗？

错误似乎发生在:

String city = scin3.next();

控制台显示:

java.util.Scanner.throwFor and java.util.Scanner.next.

下面是我的代码:

package p1;

import java.io.File;
import java.io.IOException;
import java.util.*;

class Connection {
private String departure;
private String arrival;

Connection () {};
Connection (String departure, String arrival) {
    this.departure = departure;
    this.arrival = arrival;
}
String getDeparture() {return departure;}
String getArrival() {return arrival;}
}

public class H4_20160235_1 {
public static void main(String[] args) 
{
    ArrayList<Connection> list = new ArrayList<Connection>();
    File file = new File("connection.txt");
    Scanner scin1;
    if (file.exists()) {
        try {
        scin1 = new Scanner(file);
        while (scin1.hasNext()) {
            String departure = scin1.next();
        String arrival = scin1.next();
        Connection c = new Connection(departure, arrival);
        list.add(c);                        
            }
        scin1.close();
        } catch (IOException e) {}
    }
    else {
        System.out.println("connection.txt not exist!!");
    }

    LinkedList<String> route = new LinkedList<String> ();

    System.out.println("---------------------------------------");
    System.out.println("Welcome to Flight Tour NORANG Ballon !!");
    System.out.println("---------------------------------------");
    System.out.println();

    System.out.println("<<< Flight Information >>>");
    for (Connection l: list) {
        System.out.printf("%s -> %s", l.getDeparture(), l.getArrival());
        System.out.println();
    }
    System.out.println();
    Set<String> set = new LinkedHashSet<String>();
    for (int a=0; a<list.size(); a++) 
        set.add(list.get(a).getDeparture());

    System.out.println("---------------------------------------");
    System.out.println("<<< Cities in the DB >>>");
    System.out.println("---------------------------------------");
    for (String city: set) { 
        System.out.printf("%s", city);
        System.out.println();
    }
    System.out.println("---------------------------------------");
    System.out.println();

    System.out.println("Let's plan a round-trip route!");
    Scanner scin2 = new Scanner(System.in);
    System.out.print("Enter the starting city : ");
    String departure = scin2.next();
    scin2.close();
    route.add(departure);
    System.out.printf("From %s you can fly directly to :", departure);
    System.out.println("\n");

    ArrayList<String> cities = new ArrayList<String> ();
    for (Connection l : list) {
        if (departure.equals(l.getDeparture())) {
            cities.add(l.getArrival());
            System.out.println(l.getArrival());
        }
    }
    System.out.println();
    System.out.println("---------------------------------------");

    int i = 0;
    while (true) {
        Scanner scin3 = new Scanner(System.in);
        System.out.printf("Where do you want to go from %s?", route.get(i));
        String city = scin3.next();
        scin3.close(); 
        i++;
        if (cities.contains(city) == false)
            System.out.println("***** You can't get to that city by a direct flight. *****");
        if (route.contains(city) == true) 
            break;
        ArrayList<String> cities2 = new ArrayList<String>();
        for (Connection l: list) {
            if (city.equals(l.getDeparture())) {
                cities2.add(l.getArrival());
                System.out.println(l.getArrival());
            }
        }
    }

    System.out.println("=====================================");
    System.out.println("<<<  Your Final Route  >>>");
    Iterator <String>iter = route.iterator();
    while (iter.hasNext()) {
        String temp = (String)iter.next();
        System.out.println(temp);
    }
    System.out.println("---------------------------------------");
    System.out.println();
    System.out.println("Have a nice Trip with NORANG Ballon ~");                       
}

}

下面是我的connection.txt 文件。

SanJose SanFrancisco 
SanJose Anchorage 
NewYork Anchorage 
NewYork SanJose 
NewYork SanFrancisco 
NewYork Honolulu 
Anchorage NewYork 
Anchorage SanJose 
Honolulu NewYork 
Honolulu SanFrancisco 
Denver SanJose 
SanFrancisco NewYork
SanFrancisco Honolulu 
SanFrancisco Denver

Answer 1

您必须检查是否有要获取的新 token ，其中 hasNext()方法，在每次调用 next() 之前方法。

就像您在 next() 的文档中看到的那样方法:

Finds and returns the next complete token from this scanner. A complete token is preceded and followed by input that matches the delimiter pattern. This method may block while waiting for input to scan, even if a previous invocation of hasNext() returned true. [...]

NoSuchElementException - if no more tokens are available

并在 hasNext() 中具体说明方法:

Returns true if this scanner has another token in its input. This method may block while waiting for input to scan. The scanner does not advance past any input.

此外，为了改进您的源代码，您应该在循环之外一次性实例化您的扫描仪。