Examples of java.util.Comparator

java.util.Comparator
A comparison function, which imposes a total ordering on some collection of objects. Comparators can be passed to a sort method (such as {@link Collections#sort(List,Comparator) Collections.sort} or {@link Arrays#sort(Object[],Comparator) Arrays.sort}) to allow precise control over the sort order. Comparators can also be used to control the order of certain data structures (such as {@link SortedSet sorted sets} or {@link SortedMap sorted maps}), or to provide an ordering for collections of objects that don't have a {@link Comparable natural ordering}.
The ordering imposed by a comparator c on a set of elements S is said to be consistent with equals if and only if c.compare(e1, e2)==0 has the same boolean value as e1.equals(e2) for every e1 and e2 in S.
Caution should be exercised when using a comparator capable of imposing an ordering inconsistent with equals to order a sorted set (or sorted map). Suppose a sorted set (or sorted map) with an explicit comparator c is used with elements (or keys) drawn from a set S. If the ordering imposed by c on S is inconsistent with equals, the sorted set (or sorted map) will behave "strangely." In particular the sorted set (or sorted map) will violate the general contract for set (or map), which is defined in terms of equals.
For example, suppose one adds two elements {@code a} and {@code b} such that{@code (a.equals(b) && c.compare(a, b) != 0)}to an empty {@code TreeSet} with comparator {@code c}. The second {@code add} operation will returntrue (and the size of the tree set will increase) because {@code a} and{@code b} are not equivalent from the tree set's perspective, even thoughthis is contrary to the specification of the {@link Set#add Set.add} method.
Note: It is generally a good idea for comparators to also implement java.io.Serializable, as they may be used as ordering methods in serializable data structures (like {@link TreeSet}, {@link TreeMap}). In order for the data structure to serialize successfully, the comparator (if provided) must implement Serializable.
For the mathematically inclined, the relation that defines the imposed ordering that a given comparator c imposes on a given set of objects S is:
```
 {(x, y) such that c.compare(x, y) <= 0}. 
```
The quotient for this total order is:
```
 {(x, y) such that c.compare(x, y) == 0}. 
```
It follows immediately from the contract for compare that the quotient is an equivalence relation on S, and that the imposed ordering is a total order on S. When we say that the ordering imposed by c on S is consistent with equals, we mean that the quotient for the ordering is the equivalence relation defined by the objects' {@link Object#equals(Object) equals(Object)} method(s):
```
{(x, y) such that x.equals(y)}. 
```
This interface is a member of the Java Collections Framework. @param < T> the type of objects that may be compared by this comparator @author Josh Bloch @author Neal Gafter @version 1.26, 04/21/06 @see Comparable @see java.io.Serializable @since 1.2

    }
    
    File outputDir = new File(args[k++]);
    
    URI[] uris = FileUtil.listFiles(args[k++], false, "*.xml *.xsl", "");
    Arrays.sort(uris, new Comparator() {
      public int compare(Object o1, Object o2) {
        URI u1 = (URI) o1;
        URI u2 = (URI) o2;
        return (int) (new File(u1).length() - new File(u2).length());
      }

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     * Convenience method to set up the delegate respecting any comparator specified in MetaData.
     */
    protected void initialiseDelegate()
    {
        AbstractMemberMetaData fmd = ownerSM.getClassMetaData().getMetaDataForMember(fieldName);
        Comparator comparator = SCOUtils.getComparator(fmd, ownerSM.getObjectManager().getClassLoaderResolver());
        if (comparator != null)
        {
            this.delegate = new java.util.TreeSet(comparator);
        }
        else

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    File[] files = new File[args.length];
    for (int i= 0; i < args.length; i++) {
      files[i] = new File(args[i]);
    }
    // sort by file size
    Arrays.sort(files, new Comparator() {
      public int compare(Object o1, Object o2) {
        File f1 = (File) o1;
        File f2 = (File) o2;
        return (int) (f1.length() - f2.length());
      }

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                {
                    //some datastores do not support backingStores
                }
            }
            // Set up our delegate, using a suitable comparator
            Comparator comparator = SCOUtils.getComparator(fmd, ownerSM.getObjectManager().getClassLoaderResolver());
            if (comparator != null)
            {
                this.delegate = new java.util.TreeSet(comparator);
            }
            else

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  /**
   * Test method
   */
  public static void main(String[] args) {
    Comparator cmp = new Comparator() {
      public int compare(Object o1, Object o2) {
        return ((Comparable)o1).compareTo(o2);
      }
    };


    int n = 1000000;
    if (args.length == 1)
      try {
        n = Integer.parseInt(args[0]);
      } catch (Exception e) {
        System.err.println(e);
      }
    System.out.println("Generating " + n + " random integers...");
    java.util.Random random = new java.util.Random();
    Integer[] data = new Integer[n];
    for (int i = 0; i < n; i++) {
      data[i] = new Integer(Math.abs(random.nextInt()));
//      data[i] = new Integer(i);
    }
    int[] indices;
    long time;


    System.out.print("Arrays.sort...");
    time = System.currentTimeMillis();
    Integer[] clone = (Integer[])data.clone();
    Arrays.sort(clone, cmp);
    System.out.println(System.currentTimeMillis()-time  + "ms");


    System.out.print("quicksort...");
    indices = identity(n);
    time = System.currentTimeMillis();
    sort(indices, data, cmp, false);
    System.out.println(System.currentTimeMillis()-time  + "ms");
    for (int i = 1; i < n; i++)
      if (cmp.compare(data[indices[i-1]], data[indices[i]]) > 0)
        System.err.println("proplem: quickSort at " + i);


    System.out.print("quicksort stable...");
//    indices = identity(n);
    time = System.currentTimeMillis();
    sort(indices, data, cmp, true);
    System.out.println(System.currentTimeMillis()-time + "ms");
    for (int i = 1; i < n; i++) {
      int res = cmp.compare(data[indices[i-1]], data[indices[i]]);
      if (res > 0)
        System.err.println("proplem: quickSort stable at " + i);
      if (res == 0 && indices[i-1] > indices[i])
        System.err.println("proplem: quickSort stable (not stable) at " + i);
    }


//    System.out.print("cheapsort...");
//    time = System.currentTimeMillis();
//    indices = cheapSort(data, cmp);
//    System.out.println(System.currentTimeMillis()-time + "ms");
//    for (int i = 1; i < n; i++)
//      if (cmp.compare(data[indices[i-1]], data[indices[i]]) > 0)
//        System.err.println("proplem: cheapSort at " + i);
  
    System.out.print("permutate copy...");
    time = System.currentTimeMillis();
    Object[] data_copy = permute(inverse(indices), data, true);
    System.out.println(System.currentTimeMillis()-time + "ms");
    for (int i = 1; i < n; i++)
      if (cmp.compare(data_copy[i-1], data_copy[i]) > 0)
        System.err.println("proplem: permute copy at " + i);


    System.out.print("permutate original...");
    time = System.currentTimeMillis();
    permute(inverse(indices), data, false);
    System.out.println(System.currentTimeMillis()-time + "ms");
    for (int i = 1; i < n; i++)
      if (cmp.compare(data[i-1], data[i]) > 0)
        System.err.println("proplem: permute original at " + i);
  }

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     * Convenience method to set up the delegate respecting any comparator specified in MetaData.
     */
    protected void initialiseDelegate()
    {
        AbstractMemberMetaData fmd = ownerSM.getClassMetaData().getMetaDataForMember(fieldName);
        Comparator comparator = SCOUtils.getComparator(fmd, ownerSM.getObjectManager().getClassLoaderResolver());
        if (comparator != null)
        {
            this.delegate = new java.util.TreeMap(comparator);
        }
        else

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     * Convenience method to set up the delegate respecting any comparator specified in MetaData.
     */
    protected void initialiseDelegate()
    {
        AbstractMemberMetaData fmd = ownerSM.getClassMetaData().getMetaDataForMember(fieldName);
        Comparator comparator = SCOUtils.getComparator(fmd, ownerSM.getObjectManager().getClassLoaderResolver());
        if (comparator != null)
        {
            this.delegate = new java.util.TreeMap(comparator);
        }
        else

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     * Convenience method to set up the delegate respecting any comparator specified in MetaData.
     */
    protected void initialiseDelegate()
    {
        AbstractMemberMetaData fmd = ownerSM.getClassMetaData().getMetaDataForMember(fieldName);
        Comparator comparator = SCOUtils.getComparator(fmd, ownerSM.getObjectManager().getClassLoaderResolver());
        if (comparator != null)
        {
            this.delegate = new java.util.PriorityQueue(5, comparator);
        }
        else

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     * Convenience method to set up the delegate respecting any comparator specified in MetaData.
     */
    protected void initialiseDelegate()
    {
        AbstractMemberMetaData fmd = ownerSM.getClassMetaData().getMetaDataForMember(fieldName);
        Comparator comparator = SCOUtils.getComparator(fmd, ownerSM.getObjectManager().getClassLoaderResolver());
        if (comparator != null)
        {
            this.delegate = new java.util.TreeSet(comparator);
        }
        else

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     * Convenience method to set up the delegate respecting any comparator specified in MetaData.
     */
    protected void initialiseDelegate()
    {
        AbstractMemberMetaData fmd = ownerSM.getClassMetaData().getMetaDataForMember(fieldName);
        Comparator comparator = SCOUtils.getComparator(fmd, ownerSM.getObjectManager().getClassLoaderResolver());
        if (comparator != null)
        {
            this.delegate = new java.util.PriorityQueue(5, comparator);
        }
        else

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