需要帮助理解Java中变量的作用域吗

我正在为学校做一个小程序，它读取一个数据文件，并在控制台中输出结果。我很难弄清楚为什么我的对象数组在我完成一个while循环后不能继续。代码如下：

import java.io.*;
import java.util.*;

public class order{
    private static Node nodes[];

    public static void main(String[] args) throws FileNotFoundException {
        String dataFile = "file.dat";
        indegreeCompute(dataFile);
    }

    private static void indegreeCompute(String dataFile) throws FileNotFoundException {
        Scanner scanFile = new Scanner(new File(dataFile));
        nodes = new Node[scanFile.nextInt()];
        while (scanFile.hasNextLine()) {
            scanFile.nextLine();
            int index = scanFile.nextInt();
            System.out.print("node = " + index);
            scanFile.next();
            int NumOutDegree = scanFile.nextInt();
            nodes[index].outDegree = NumOutDegree;
            System.out.print(" outDegree = " + nodes[index].outDegree);
            nodes[index].adjNodes = new int[NumOutDegree];
            scanFile.next();
            System.out.print(" adjNodes = [");
            for ( int i = 0; i < nodes[index].outDegree; i ++ ) {
                nodes[index].adjNodes[i] = scanFile.nextInt();
                if (i < nodes[index].outDegree - 1)
                    System.out.print(nodes[index].adjNodes[i] + ", ");
                else
                    System.out.print(nodes[index].adjNodes[i]);
            }
            System.out.print("]");
            System.out.println();
        }

        for (int i = 0; i < nodes.length; i ++) {
            int outDegree = nodes[i].outDegree;
            for(int k = 0; k < outDegree; k ++) {
                int adjNode = nodes[i].adjNodes[k];
                nodes[adjNode].inDegree ++;
            }
        }
        scanFile.close();
    }
}

任何帮助或解释，以帮助我理解将不胜感激。谢谢

以下是该文件的内容：

14 //numNodes; space after '(' and before ')' to simplify reading the file
 0 (  1 ): 10 //node ( outdegree ): adjNodes in arbitrary order
 1 ( 10 ):  0  5  8 10  6  9  7 11 12 13
 2 (  1 ):  7
 3 (  3 ):  1  10 11
 4 (  3 ):  0  1  5
 5 (  3 ):  6  7  10
 6 (  2 ):  7 10
 7 (  5 ):  8 10  12 11 13
 8 (  1 ): 13
 9 (  1 ):  0
10 (  0 ):
11 (  0 ):
12 (  2 ): 10 11
13 (  1 ): 12

---

在为节点[index]的属性指定任何值之前，应先设置节点[index]=new Node（）。节点类的属性不应该是静态的，因为每个节点都应该有自己的值

因为节点数组中的每个元素都将为null，除非为其设置值。在代码中，当您将值设置为nodes[index].outDegree时，实际上是在设置Node.outDegree的值，而nodes[index]仍然为空。最后，你会得到一个满是null的数组

---

总之，这里有两个错误。错误地使用静态关键字，并且在使用对象数组项之前忘记初始化它

以下内容应该适合您

    public class Node {
     //public static  int inDegree, outDegree, adjNodes[]; // static was causing the problem
     public int inDegree, outDegree, adjNodes[];
    }


public class order{
    private static Node nodes[];

    public static void main(String[] args) throws FileNotFoundException {
        String dataFile = "file.dat";
        indegreeCompute(dataFile);
    }

    private static void indegreeCompute(String dataFile) throws FileNotFoundException {
        Scanner scanFile = new Scanner(new File(dataFile));
        nodes = new Node[scanFile.nextInt()];
        for(int l= 0 ; l <nodes.length ; l++) {
            nodes[l] = new Node();
        }
        while (scanFile.hasNextLine()) {
            scanFile.nextLine();
            int index = scanFile.nextInt();
            System.out.print("node = " + index);
            scanFile.next();
            int NumOutDegree = scanFile.nextInt();
            nodes[index].outDegree = NumOutDegree;
            System.out.print(" outDegree = " + nodes[index].outDegree);
            nodes[index].adjNodes = new int[NumOutDegree];
            scanFile.next();
            System.out.print(" adjNodes = [");
            for ( int i = 0; i < nodes[index].outDegree; i ++ ) {
                nodes[index].adjNodes[i] = scanFile.nextInt();
                if (i < nodes[index].outDegree - 1)
                    System.out.print(nodes[index].adjNodes[i] + ", ");
                else
                    System.out.print(nodes[index].adjNodes[i]);
            }
            System.out.print("]");
            System.out.println();
        }

        for (int i = 0; i < nodes.length; i ++) {
            int outDegree = nodes[i].outDegree;
            for(int k = 0; k < outDegree; k ++) {
                int adjNode = nodes[i].adjNodes[k];
                nodes[adjNode].inDegree ++;
            }
        }
        scanFile.close();
    }
}

公共类节点{
//public static int inDegree、outDegree、adjNodes[]；//问题是由static引起的
公共int-inDegree、outDegree、adjNodes[]；
}
公共阶级秩序{
私有静态节点[]；
公共静态void main（字符串[]args）引发FileNotFoundException{
字符串dataFile=“file.dat”；
indegreeCompute（数据文件）；
}
私有静态void indegreeCompute（字符串数据文件）引发FileNotFoundException{
扫描仪扫描文件=新扫描仪（新文件（数据文件））；
节点=新节点[scanFile.nextInt（）]；
对于（int l=0；l）你能发布topoOrder.dat的内容吗？你程序的输出（第一个for循环）与你期望的匹配吗？是的，第一个循环中的输出是完美的。我只是在第二个循环中遇到了问题。
    public class Node {
     //public static  int inDegree, outDegree, adjNodes[]; // static was causing the problem
     public int inDegree, outDegree, adjNodes[];
    }


public class order{
    private static Node nodes[];

    public static void main(String[] args) throws FileNotFoundException {
        String dataFile = "file.dat";
        indegreeCompute(dataFile);
    }

    private static void indegreeCompute(String dataFile) throws FileNotFoundException {
        Scanner scanFile = new Scanner(new File(dataFile));
        nodes = new Node[scanFile.nextInt()];
        for(int l= 0 ; l <nodes.length ; l++) {
            nodes[l] = new Node();
        }
        while (scanFile.hasNextLine()) {
            scanFile.nextLine();
            int index = scanFile.nextInt();
            System.out.print("node = " + index);
            scanFile.next();
            int NumOutDegree = scanFile.nextInt();
            nodes[index].outDegree = NumOutDegree;
            System.out.print(" outDegree = " + nodes[index].outDegree);
            nodes[index].adjNodes = new int[NumOutDegree];
            scanFile.next();
            System.out.print(" adjNodes = [");
            for ( int i = 0; i < nodes[index].outDegree; i ++ ) {
                nodes[index].adjNodes[i] = scanFile.nextInt();
                if (i < nodes[index].outDegree - 1)
                    System.out.print(nodes[index].adjNodes[i] + ", ");
                else
                    System.out.print(nodes[index].adjNodes[i]);
            }
            System.out.print("]");
            System.out.println();
        }

        for (int i = 0; i < nodes.length; i ++) {
            int outDegree = nodes[i].outDegree;
            for(int k = 0; k < outDegree; k ++) {
                int adjNode = nodes[i].adjNodes[k];
                nodes[adjNode].inDegree ++;
            }
        }
        scanFile.close();
    }
}