JAVAM：Sort Java Vector

Question

什麼是在JAVAME中對Java Vector進行排序的最好和最有效的方法。

我的對象有五個屬性，我想按屬性price排序，該屬性的類型爲double。在我的向量中，我將有最多150個項目。示例代碼將不勝感激。

Thanx爲您的時間。

Answer 1

使用Collections.sort（列表< T> vector，比較器< T> c）方法。如果Java ME中沒有這樣的方法，只需從Java SE複製它。它使用合併排序算法，所以它不會複製太多。

從JavaSE的

Answer 2

import java.lang.reflect.Field; 
import java.util.*; 

public class Sorter { 

    public static List sort(List list, String fieldName, boolean asc) { 
     Comparator c = new FieldComparator(fieldName, asc); 
     Collections.sort(list, c); 
     return list; 
    } 

    public static int compareNumbers(Number n1, Number n2) { 
     double d1 = n1.doubleValue(); 
     double d2 = n2.doubleValue(); 

     if (d1 < d2) { 
      return -1; 
     } 
     if (d2 < d1) { 
      return 1; 
     } 
     return 0; 
    } 

    public static int compareDates(Date d1, Date d2) { 
     long l1 = d1.getTime(); 
     long l2 = d2.getTime(); 

     if (l1 < l2) { 
      return -1; 
     } 
     if (l2 < l1) { 
      return 1; 
     } 
     return 0; 
    } 

    public static int compareStrings(String s1, String s2) { 
     return s1.compareTo(s2); 
    } 

    public static Object getFieldValue(Object obj, String fn) { 
     try { 
      Class clazz = obj.getClass(); 
      Field f = null; 
      try { 
       f = clazz.getDeclaredField(fn); 
      } catch (Exception e) {} 

      while (f == null && clazz.getSuperclass() != null) { 
       clazz = clazz.getSuperclass(); 
       try { 
        f = clazz.getDeclaredField(fn); 
       } catch (Exception e) {} 
      }//while 

      if (f != null) { 
       f.setAccessible(true); 
       return f.get(obj); 
      } 
     } catch (IllegalAccessException e) {} 
     return null; 
    } 

    protected static class FieldComparator implements Comparator { 
     String fieldName; 
     int asc; 

     protected FieldComparator(String fieldName, boolean asc) { 
      this.fieldName = fieldName; 
      this.asc = asc ? 1 : -1; 
     } 

     public int compare(Object o1, Object o2) { 
      if (o1 == null) { 
       if (o2 == null) { 
        return 0; 
       } else { 
        return -1 * asc; 
       } 
      } 

      if (o2 == null) { 
       return asc; 
      } 

      //compare fields 
      Object fieldValue1 = getFieldValue(o1, fieldName); 
      Object fieldValue2 = getFieldValue(o2, fieldName); 

      if (fieldValue1 == null) { 
       if (fieldValue2 == null) { 
        return 0; 
       } else { 
        return -1 * asc; 
       } 
      } 

      if (fieldValue2 == null) { 
       return asc; 
      } 

      //both field values aren't nulls 
      if (fieldValue1 instanceof Number && fieldValue2 instanceof Number) { 
       return compareNumbers((Number) fieldValue1, (Number) fieldValue2) * asc; 
      } else if (fieldValue1 instanceof Date && fieldValue2 instanceof Date) { 
       return compareDates((Date) fieldValue1, (Date) fieldValue2) * asc; 
      } else { 
       return compareStrings(fieldValue1.toString(), fieldValue2.toString()) * asc; 
      } 
     } 
    } 

    public static void main(String[] args) { 
     ArrayList source = new ArrayList(); 
     source.add(new TestNumber(5)); 
     source.add(new TestNumber(1)); 
     source.add(new TestNumber(4)); 
     source.add(new TestNumber(2)); 
     source.add(new TestNumber(3)); 

     List dest = sort(source, "value", true); 
     out(dest); 

     source = new ArrayList(); 
     source.add(new TestString("cc")); 
     source.add(new TestString("dd")); 
     source.add(new TestString("bb")); 
     source.add(new TestString("ee")); 
     source.add(new TestString("aa")); 

     dest = sort(source, "value", false); 
     out(dest); 
    } 

    private static class TestNumber { 
     private int value; 

     public TestNumber(int v) { 
      value = v; 
     } 

     public String toString() { 
      return "" + value; 
     } 
    } 

    private static class TestString { 
     private String value; 

     public TestString(String v) { 
      value = v; 
     } 

     public String toString() { 
      return "" + value; 
     } 
    } 

    private static void out(List list) { 
     for (Object obj : list) { 
      System.out.println("" + obj.toString()); 
     } 
     System.out.println("----------------------------"); 
    } 
} 

Answer 3

調整代碼：

public static void sort(List<YourObject> list) { 
    Object[] a = list.toArray(); 
    sort(a); 
    ListIterator<YourObject> i = list.listIterator(); 
    for (int j=0; j<a.length; j++) { 
     i.next(); 
     i.set((YourObject)a[j]); 
    } 
} 

public static void sort(YourObject[] a) { 
    YourObject[] aux = (YourObject[])a.clone(); 
    mergeSort(aux, a, 0, a.length, 0); 
} 

private static void mergeSort(YourObject[] src, 
       YourObject[] dest, 
       int low, 
       int high, 
       int off) { 
int length = high - low; 

// Insertion sort on smallest arrays 
    if (length < INSERTIONSORT_THRESHOLD) { 
     for (int i=low; i<high; i++) 
      for (int j=i; j>low && 
     dest[j-1].getPrice()-dest[j].getPrice()>0; j--) 
       swap(dest, j, j-1); 
     return; 
    } 

    // Recursively sort halves of dest into src 
    int destLow = low; 
    int destHigh = high; 
    low += off; 
    high += off; 
    int mid = (low + high) >>> 1; 
    mergeSort(dest, src, low, mid, -off); 
    mergeSort(dest, src, mid, high, -off); 

    // If list is already sorted, just copy from src to dest. This is an 
    // optimization that results in faster sorts for nearly ordered lists. 
    if (src[mid-1].getPrice()-src[mid].getPrice() <= 0) { 
     System.arraycopy(src, low, dest, destLow, length); 
     return; 
    } 

    // Merge sorted halves (now in src) into dest 
    for(int i = destLow, p = low, q = mid; i < destHigh; i++) { 
     if (q >= high || p < mid && src[p].getPrice()-src[q].getPrice()<=0) 
      dest[i] = src[p++]; 
     else 
      dest[i] = src[q++]; 
    } 
}