java - Arraylist 将第一个元素生成为 null

Question

我一直在尝试实现 Dijkstra 算法。以下是读取输入的代码:

            System.out.println("Enter the number of Cities ");
            int no_Of_Cities = scannerObj.nextInt();
            List<Vertex> Vertices = new ArrayList<Vertex>(no_Of_Cities) ;
            for (int itr = 0; itr < no_Of_Cities; itr++){
                  System.out.println("Enter the details for city "+itr+": ");
                  System.out.println("Name of the vertex: ");
                  String name = new String(scannerObj.nextLine());
                  Vertex vertexObj = new Vertex(name);
                  Vertices.add(vertexObj);
                  }
            display(Vertices);

显示函数如下:

      public static void display(List<Vertex> vertices){
            int length = vertices.size();
            for(int i =0;i<length;i++){
                  System.out.println();
                  System.out.println("Entry for i ="+i+" is: "+vertices.get(i).getName());
            }
      }

当我尝试执行代码时，以下是我得到的输出:

Enter the number of Cities 3

Enter the details for city 0:

Name of the vertex: a

Please enter the details for city 1:

Name of the vertex: b

Please enter the details for city 2:

Name of the vertex: c

Entry for i =0 is:

Entry for i =1 is: a

Entry for i =2 is: b

谁能解释一下我哪里出错了？

注意:Vertex 是另一个类，它只包含顶点的必要细节，如名称和边数组。

Answer 1

添加scannerObj.nextLine();

之后

int no_Of_Cities = scannerObj.nextInt();

这将消耗包含您刚刚读取的 int 的行的末尾，并防止在您首次调用 String name = new String(scannerObj.nextLine( ));