获取“主要” java.lang.UnsupportedOperationException

Question

在执行此代码时，我在第81行上收到了java.lang.UnsupportedOperationException。我知道发布整个代码违反了赌注的做法，但是我认为除非发布整个代码，否则传达我正在做的事情将非常困难。

基本上，我想从列表中删除所有出现的元素，所以我正在做List.removeAll（Collection）。我不明白在81号线上我在做什么错。谢谢您的帮助！

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.util.*;
import java.util.Map.Entry;;


public class MinCutClass {

    /**
     * @param args
     */
    private HashMap verticeMap ;
    private List edgeList ;


    public MinCutClass()
    {
          verticeMap = new HashMap();
          edgeList = new ArrayList();
    }

    public static void main(String[] args)

    {
        // TODO Auto-generated method stub
        MinCutClass minCutObj = new MinCutClass();

        minCutObj.populateVertices();
        minCutObj.printVerticeMap();
        minCutObj.printVerticeMap1();

        minCutObj.populateEdges();

        //minCutObj.printEdgeList();

        minCutObj.findMinCut();

//      minCutObj.printEdgeList();
    //  minCutObj.printVerticeMap();


    }

    private void printEdgeList()
    {
        Iterator i = edgeList.iterator();

        while(i.hasNext())
        {

            System.out.println(i.next());
        }

    }

    private void printVerticeMap()
    {

        Set s = verticeMap.entrySet();
        Iterator i = s.iterator();


        while(i.hasNext())
        {
            Entry e = (Entry)i.next();

            System.out.println("Key :" + e.getKey() + " Value :" + e.getValue());

        }

    }

    private void printVerticeMap1()
    {
        Collection c = new TreeSet();
        c.add("2");
        List temp = (List)verticeMap.get("1");
        System.out.println(temp.getClass().getName());
        temp.removeAll(c);

    }

    private void findMinCut()
    {


        while (verticeMap.keySet().size() > 2 ) // as long as there are more than two vertices
        {

            int randomEdgeIndex = chooseRandomEdgeIndex(); //choose a random edge basically any random index in edgeList
            String randomEdgeChosen = (String)edgeList.get(randomEdgeIndex);

            //Edge contraction

            //1. remove the edges from edgeList. We want to avoid self loops. There may exist many edges of this type.
            Collection c = new TreeSet();
            c.add(edgeList.get(randomEdgeIndex));
            edgeList.removeAll(c); //removeAll , all edges are removed
            c.clear();

            //get edge vertices
            String [] tempArr = randomEdgeChosen.split("_");
            String v1 =  tempArr[0];
            String v2 = tempArr[1];


            //2.a Delete v2 from v1 vertices list, the contracting edge vanishes. Please note, all parallel edges are also being removed as they create self loops.
            List tempListV1 = (List)verticeMap.get(v1);
            c.add(v2);
            tempListV1.removeAll(c);
            c.clear();


            //2.b Now delete v1 from v2 vertices list, the contracting edge and all parallel edges are removed as they create self loops. 
            List tempListV2 = (List)verticeMap.get(v2);
            c.add(v1);
            tempListV2.removeAll(c);
            c.clear();

            //3. Now add all vertices v2 is connected with in v1 list because the resultant merged node is v1
            Iterator i = tempListV2.iterator();

            List tempListEle;

            while (i.hasNext())
            {
                String ele = (String)i.next();
                tempListEle = (List)verticeMap.get(ele); //get the vertice list for the current element (from v2 list) being considered  as v1 has to be added to that list and v2 removed.


                tempListV1.add(ele);
                //tempListV2.remove(ele); //this is not needed , as entry for v2 in verticeMap will be deleted

                tempListEle.add(v1);
                tempListEle.remove(v2);

            }


            verticeMap.remove(v2); //once all v2 elements are added to entries for all v2 elements are also updated remove entry for v2 in verticeMap

        }


    }

    private int chooseRandomEdgeIndex()
    {
        return new Random().nextInt(edgeList.size()); 
    }

    private void populateVertices()
    {
        List list = readFile(); // get a list of String arrays
        Iterator i = list.iterator(); 
        while(i.hasNext())
        {
            String[] tempArr  = (String[])i.next(); // get current String array
            String node = tempArr[0]; //get the node number

            tempArr = Arrays.copyOfRange(tempArr, 1, tempArr.length ); //create a String array with 0th element removed


            //System.out.println(node + "" + Arrays.asList(tempArr) + this.verticeMap.getClass().getName());
            //System.out.println(node + "" + Arrays.asList(tempArr));

            this.verticeMap.put(node, Arrays.asList(tempArr)); // put the node and the nodes it has edges with in a HashMap

            //System.out.println(node + "" + verticeMap.get(node).toString());

        }


        //System.out.println("1" + "" + verticeMap.get("1").toString());

    }

    private void populateEdges()
    {
        List list = readFile(); // get a list of String arrays
        Iterator i = list.iterator(); 
        while(i.hasNext())
        {
            String[] tempArr  = (String[])i.next(); // get current String array
            String node = tempArr[0]; //get the node number

            for(int count = 1 ; count <= tempArr.length - 1; count++) 
            {
                if(getInt(node) < getInt(tempArr[count]) ) //add the edge to the edgeList only if the node is smaller than other node being considered. This way you only add each edge only once for each pair of vertices.
                {

                    //System.out.println(node + tempArr[count]);
                    edgeList.add(""+node+"_"+tempArr[count]);

                }
            }
        }

//       i = edgeList.iterator();
//       while (i.hasNext())
//       {
//           System.out.println(i.next().toString());
//           
//       }

    }

    private List readFile()
    {
        List list = new ArrayList(); // list of String arrays
            try
            {
                 FileInputStream fstream = new FileInputStream("C:/Users/ankura/Desktop/KargerAdj.txt");

                  DataInputStream in = new DataInputStream(fstream);
                  BufferedReader br = new BufferedReader(new InputStreamReader(in));
                  String strLine;
                  String[] strArr;
                  while ((strLine = br.readLine()) != null)   
                  {

                      strLine = strLine.trim();
                      strArr = strLine.split("\\W+");

                      list.add(strArr);

                  }

                  in.close();

             }

             catch (Exception e)
             {
                //Catch exception if any
              System.err.println("Error: " + e.getMessage());
             }

            return list;

    }


    public int getInt(Object o)
    {

        return Integer.parseInt((String)o);

    }
}

输出/ StackTrace：

Exception in thread "main" java.lang.UnsupportedOperationException
    at java.util.AbstractList.remove(Unknown Source)
    at java.util.AbstractList$Itr.remove(Unknown Source)
    at java.util.AbstractCollection.removeAll(Unknown Source)
    at MinCutClass.printVerticeMap1(MinCutClass.java:81)
    at MinCutClass.main(MinCutClass.java:32)
Key :3 Value :[2, 4]
Key :2 Value :[1, 3, 4]
Key :1 Value :[2, 4]
Key :4 Value :[1, 2, 3]
java.util.Arrays$ArrayList

Answer 1

  Arrays.asList(tempArr)

返回由该数组支持的
固定大小的 列表。您不能从中删除元素（或向其中添加元素）。

请注意，由Arrays.asList返回的列表仍受该数组支持，因此当您更新列表中的元素时，它也会在数组中对其进行更改。

如果您需要可修改的副本，请使用

new ArrayList(Arrays.asList(tempArr))