拓扑排序实现代码中的逻辑错误

Question

我使用队列实现了拓扑排序，但是，Vertex类中存在一个逻辑错误，导致此代码无法正常工作。

public class TopologicalSort {

public void TopSort(ArrayList<Vertex> vertices) throws CycleFoundException
{   
    int i;      
    int j;

    for (i = 0; i < vertices.size(); i++)
    {   
        for(j = 0; j < vertices.get(i).getAdjacentVertices(vertices.get(i)).size(); j++)
        {
            vertices.get(i).AdjacentVertices.get(j).indegree++;             
        }
    }

    Queue<Vertex> q = new LinkedList<Vertex>();
    int counter = 0;

    for(i = 0; i < vertices.size(); i++)
    {
        if(vertices.get(i).indegree == 0)
            q.add(vertices.get(i));
    }
    while(!q.isEmpty())
    {
        Vertex v = q.remove();
        v.topNum = counter++;

        for (i = 0; i < vertices.size(); i++)
        {
            for(j = 0; j < vertices.get(i).getAdjacentVertices(vertices.get(i)).size(); j++)
            {   System.out.println(vertices.get(i).AdjacentVertices.get(j).indegree);
                if(--(vertices.get(i).AdjacentVertices.get(j).indegree) == 0)
                {
                    q.add(vertices.get(i).AdjacentVertices.get(j));
                    System.out.println(q.toArray()[i]);
                }
            }
        }
    }
    if(counter != vertices.size())
        throw new CycleFoundException();        
}   

}

public class Vertex {
String name;
int indegree;
ArrayList<Vertex> AdjacentVertices;
public int topNum;

public Vertex(String name, int indegree, ArrayList<Vertex> AdjacentVertices)
{
    this.name = name;
    this.indegree = indegree;
    this.AdjacentVertices =  new ArrayList<Vertex>();   
}

public ArrayList<Vertex> getAdjacentVertices(Vertex a) {

    while (AdjacentVertices.size() != 0)
    {
        for (int i = 0; i < AdjacentVertices.size(); i++)
        AdjacentVertices.remove(i);
    }

    switch (a.name)
    {
        case "S":
        {
            Vertex A = new Vertex("A", 0, AdjacentVertices);
            AdjacentVertices.add(A);
            Vertex D = new Vertex("D", 0, AdjacentVertices);
            AdjacentVertices.add(D);
            Vertex G = new Vertex("G", 0, AdjacentVertices);
            AdjacentVertices.add(G);            
            break;
        }
        case "A":
        {
            Vertex B = new Vertex("B", 0, AdjacentVertices);
            AdjacentVertices.add(B);
            Vertex E = new Vertex("E", 0, AdjacentVertices);
            AdjacentVertices.add(E);            
            break;
        }
        case "B":
        {
            Vertex C = new Vertex("C", 0, AdjacentVertices);
            AdjacentVertices.add(C);
            break;
        }
        case "C":
        {
            Vertex D = new Vertex("D", 0, AdjacentVertices);
            AdjacentVertices.add(D);
            break;
        }
        case "D":
        {
            Vertex E = new Vertex("E", 0, AdjacentVertices);
            AdjacentVertices.add(E);
            break;
        }
        case "E":
        {
            Vertex C = new Vertex("C", 0, AdjacentVertices);
            AdjacentVertices.add(C);
            Vertex F = new Vertex("F", 0, AdjacentVertices);
            AdjacentVertices.add(F);
            Vertex I = new Vertex("I", 0, AdjacentVertices);
            AdjacentVertices.add(I);    
            break;
        }
        case "F":
        {
            Vertex C = new Vertex("C", 0, AdjacentVertices);
            AdjacentVertices.add(C);
            Vertex T = new Vertex("T", 0, AdjacentVertices);
            AdjacentVertices.add(T);        
            break;
        }
        case "G":
        {
            Vertex D = new Vertex("D", 0, AdjacentVertices);
            AdjacentVertices.add(D);
            Vertex E = new Vertex("E", 0, AdjacentVertices);
            AdjacentVertices.add(E);
            Vertex H = new Vertex("H", 0, AdjacentVertices);
            AdjacentVertices.add(H);    
            break;
        }
        case "H":
        {
            Vertex E = new Vertex("E", 0, AdjacentVertices);
            AdjacentVertices.add(E);
            Vertex I = new Vertex("I", 0, AdjacentVertices);
            AdjacentVertices.add(I);        
            break;
        }
        case "I":
        {
            Vertex F = new Vertex("F", 0, AdjacentVertices);
            AdjacentVertices.add(F);
            Vertex T = new Vertex("T", 0, AdjacentVertices);
            AdjacentVertices.add(T);        
            break;
        }
        case "T": break;



    }   
    return AdjacentVertices;
}

@Override
public String toString() {
    return name;
}

}

在Vertex类中，在getAdjacentVertices方法中，第一个while循环导致每次对此方法进行新调用时列表变为空，但是如果没有此循环，则arraylist的大小将每次乘以2调用此函数。我似乎无法想到修改getAdjacentVertices以正常工作。有没有办法修改getAdjacentVertices方法，以便我可以删除while循环，并且每次调用此方法时arraylist都不会乘以2？提前感谢您的帮助。