QuickList用于ArrayList <Object>

Question

我似乎在快速排序方法中遇到了一些问题.我正在尝试使用我的quicksort方法对对象的ArrayList进行排序.我正在使用Apache POI库从excel文件中提取数据,我将这些数据添加到我的arraylist中.我已经通过在应用quicksort方法之前打印出arraylist来确认我的arraylist不是空的.

我的问题似乎是在传入我的对象的arraylist之后它被重置为null并且arraylist的大小变为0.我在我的quicksort方法中尝试从arraylist获取一个对象时得到了一个java IndexOutOfBounds异常.任何帮助将不胜感激,谢谢!

这是我的主要课程:

编辑我使用下面给出的解决方案解决了我的问题,但我仍然不明白为什么我的快速排序功能不起作用.如果有人能看一下quicksort功能并告诉我哪里出错了,我将不胜感激.谢谢 !

public class Test {


private static ArrayList<Object> incom = new ArrayList<Object>();


private static int period;
private static String termination = "yes";
private static int pivotVal;

private static ArrayList<String> treatment_name = new ArrayList();
private static ArrayList<Integer> treatment_cstart = new ArrayList();
private static ArrayList<Integer> treatment_cend = new ArrayList();
private static ArrayList<Integer> treatment_cost = new ArrayList();
private static ArrayList<Integer> bridge_part = new ArrayList();
private static ArrayList<Integer> budget = new ArrayList();

private static Scanner input = new Scanner(System.in);
private static Scanner alt = new Scanner(System.in).useDelimiter("\n");

public static void main(String[] args) 
{   

    processFile();


}

public static void processFile(){
    try {
        POIFSFileSystem fs      =
            new POIFSFileSystem(new FileInputStream("Book2.xls"));
        HSSFWorkbook wb = new HSSFWorkbook(fs);

        HSSFSheet sheet =wb.getSheet("Table0");
        RowProcessor ip = IncomeProcessor.getInstance();
        Object [] incomes = ip.process(sheet);

        for (int i=0; i<incomes.length; i++)
          incom.add(incomes[i]);

        for (int i=0; i<incom.size(); i++)
        {
            Income income = (Income)incom.get(i);
            System.out.println(income.getBridgeID() + " " + income.getDeckState());
        }


          incom = quicksort(incom);

    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}



public static ArrayList<Object> quicksort(ArrayList<Object> income){

    int pivot = income.size()/2;
    int samePivotVal = 0;
    ArrayList<Object> greater = new ArrayList<Object>();
    ArrayList<Object> lesser = new ArrayList<Object>();

    Income pivotIncome = (Income) income.get(pivot);
    pivotVal = pivotIncome.getDeckState();

    Income in;
    for(int i=0; i<income.size() ;i++){
        in = (Income)income.get(i);
        if(in.getDeckState() > pivotVal)
            greater.add(in);
        else if(in.getDeckState() < pivotVal)
            lesser.add(in);
        else 
            samePivotVal++;
    }


    lesser = quicksort(lesser);
    for(int i=0; i<samePivotVal; i++)
        lesser.add(pivotIncome);

    greater = quicksort(greater);

    ArrayList<Object> sorted = new ArrayList<Object>();

    for(Object result : lesser)
        sorted.add(result);

    for(Object result : greater)
        sorted.add(result);

    return sorted;
    }



}

Answer 1

如果使用Java的内置排序方法,将会更容易(也更好).

public static void processFile(){ 
    //...

    Collections.sort(incom, new IncomComparator());
    //...
}


class IncomComparator implements Comparator<Object> {
    @Override
    public int compare(Object o1, Object o2) {
        /* compare logic goes here
           return a negative number when o1 < o2
                  a positive number when o1 > o2
                  0 when o1 == o2
        */ 
        return 0;
    }

}

或者以更简单的方式

public static void processFile(){ 
    //...

    Collections.sort(incom, new Comparator<Object>() {
        @Override
        public int compare(Object o1, Object o2) {
           /* compare logic goes here
               return a negative number when o1 < o2
                  a positive number when o1 > o2
                  0 when o1 == o2
           */ 
           return 0;
        }
    });
    //...
}

你可以在这里看到更多的例子.