Java Doc By Examples | |

Prev Class | Next Class | Frames | No Frames |

Summary: Nested | Field | Method | Constr | Detail: Nested | Field | Method | Constr |

**Known Subinterfaces:**- UserVersionType

**Known Implementing Classes:**- BeanComparator, BinaryType, BooleanComparator, BooleanComparator, CalendarComparator, Collator, ComparableComparator, ComparableComparator, ComparableComparator, ComparatorChain, CompoundComparator, Cookie, Cookie2, CookiePathComparator, DefaultFileComparator, DirectoryProperty.PropertyComparator, ExtensionFileComparator, FixedOrderComparator, InvertibleComparator, JRYComparator, KeyedValueComparator, LastModifiedFileComparator, NameFileComparator, NullComparator, NullSafeComparator, OrderComparator, PathFileComparator, PropertyComparator, ReverseComparator, RuleBasedCollator, SizeFileComparator, Sorter, StringEncoderComparator, TermVectorEntryFreqSortedComparator, TransformingComparator, XPathComparator

`public interface `**Comparator<T>**

A comparison function, which imposes a *total ordering* on some
collection of objects. Comparators can be passed to a sort method (such as
`Collections.sort`) to allow precise control over the sort order.
Comparators can also be used to control the order of certain data
structures (such as `TreeSet` or `TreeMap`).*quotient* for this total order is:`compare` that the
quotient is an *equivalence relation* on `S`, and that the
natural 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 natural ordering is the
equivalence relation defined by the objects' `equals(Object)`
method(s):

The ordering imposed by a Comparator `c` on a set of elements
`S` is said to be *consistent with equals* if and only if
`(compare((Object)e1, (Object)e2)==0)` has the same boolean value as
`e1.equals((Object)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, if one adds two keys `a` and `b` such that
`(a.equals((Object)b) && c.compare((Object)a, (Object)b) != 0)` to a
sorted set with comparator `c`, the second `add` operation
will return false (and the size of the sorted set will not increase)
because `a` and `b` are equivalent from the sorted set's
perspective.

Note: It is generally a good idea for comparators to implement
`java.io.Serializable`, as they may be used as ordering methods in
serializable data structures (like `TreeSet`, `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 *total order* that a given comparator `c` imposes on a
given set of objects `S` is:

{(x, y) such that c.compare((Object)x, (Object)y) <= 0}.The

{(x, y) such that c.compare((Object)x, (Object)y) == 0}.It follows immediately from the contract for

{(x, y) such that x.equals((Object)y)}.

This interface is a member of the ../../../guide/collections/index.html"> Java Collections Framework.

**Since:**- 1.2

**See Also:**`Comparable`

,`Arrays.sort(Object[], Comparator)`

,`TreeMap`

,`TreeSet`

,`SortedMap`

,`SortedSet`

,`Serializable`

## Method Summary

`int`

`compare(T o1, T o2)`

- Compares its two arguments for order.

`boolean`

public int compare(T o1, T o2)

Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.The implementor must ensure that

sgn(compare(x, y)) == -sgn(compare(y, x))for allxandy. (This implies thatcompare(x, y)must throw an exception if and only ifcompare(y, x)throws an exception.)The implementor must also ensure that the relation is transitive:

((compare(x, y)>0) && (compare(y, z)>0))impliescompare(x, z)>0.Finally, the implementer must ensure that

compare(x, y)==0implies thatsgn(compare(x, z))==sgn(compare(y, z))for allz.It is generally the case, but

notstrictly required that(compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals."

Parameters:`o1`

- the first object to be compared.`o2`

- the second object to be compared.

Returns:- a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.

Throws:`ClassCastException`

- if the arguments' types prevent them from being compared by this Comparator.

**Usages and Demos :**

View More Examples of compare(T o1,T o2)

1: 2: import java.util.Comparator;3: import java.util.Iterator; 4: ... 5: Object y = result.first(); 6:Comparatorc = set.comparator(); 7: if (c != null) 8: ... 9: return c.compare(x, y)== 0 ? y : null; 10: else

View Full Code Here

import javax.swing.tree.*;

import java.util.**Comparator;**

...

public class SortTreeModel extends DefaultTreeModel {

private**Comparator **comparator;

...

if (cc == 1) {

return comparator.**compare(child, parent.getChildAt(0)**) <= 0 ? 0 : 1;

}

...

if (i1 == i2) {

return comparator.**compare(child, parent.getChildAt(i1)**) <= 0 ? i1

View Full Code Here

import java.util.

...

public class SortTreeModel extends DefaultTreeModel {

private

...

if (cc == 1) {

return comparator.

}

...

if (i1 == i2) {

return comparator.

View Full Code Here

1: 2: import java.util.Comparator;3: 4: ... 5: 6: public Heap(int capacity,Comparatorcmp) 7: throws IllegalArgumentException { 8: ... 9: 10: return cmp_.compare(a, b); 11: }

View Full Code Here

1: 2: import java.util.Comparator;3: import java.text.Collator; 4: ... 5: 6: public class AtomicComparer implementsComparator,java.io.Serializable { 7: 8: ... 9: privateComparatorcollator; 10: 11: ... 12: } else if (a instanceof String) { 13: return collator.compare(a, b)== 0;

View Full Code Here

public boolean equals(Object obj)

Indicates whether some other object is "equal to" this Comparator. This method must obey the general contract ofObject.equals(Object). Additionally, this method can returntrueonlyif the specified Object is also a comparator and it imposes the same ordering as this comparator. Thus,`comp1.equals(comp2)`

implies thatsgn(comp1.compare(o1, o2))==sgn(comp2.compare(o1, o2))for every object referenceo1ando2.Note that it is

alwayssafenotto overrideObject.equals(Object). However, overriding this method may, in some cases, improve performance by allowing programs to determine that two distinct Comparators impose the same order.

Parameters:`obj`

- the reference object with which to compare.

Returns:`true`

only if the specified object is also a comparator and it imposes the same ordering as this comparator.

See Also:`Object.equals(Object)`

,`Object.hashCode()`

**Usages and Demos :**

View More Examples of equals(Object obj)

1: import java.io.Serializable; 2: import java.util.Comparator;3: 4: ... 5: public class ReverseComparator implementsComparator,Serializable { 6: 7: ... 8: 9: public ReverseComparator(Comparatorcomparator) { 10: if(comparator != null) { 11: ... 12: return false; 13: } else if(that.getClass().equals(this.getClass())) {

View Full Code Here

1: List children; 2:ComparatornodeComparator; 3: boolean ready; 4: ... 5: 6: public void init(GenericTreeNode parent,ComparatornodeComparator, 7: Object node, List children, Class childClass) { 8: ... 9: } else { 10:ComparatorinComp = in.getNodeComparator(); 11: if ((this == nodeComparator) 12: ... 13: || (nodeComparator == inComp) 14: || (nodeComparator.equals(inComp))) {

View Full Code Here

1: 2: static final int compare(Object o1, Object o2,Comparatorc) 3: { 4: ... 5: 6: public static int binarySearch(List l, Object key,Comparatorc) 7: { 8: ... 9: for (int i = 0, j = target.size(); j <= ssize; i++, j++) 10: if (source.subList(i, j).equals(target)) 11: return i; 12: ... 13: for (int i = ssize - target.size(), j = ssize; i >= 0; i--, j--) 14: if (source.subList(i, j).equals(target))

View Full Code Here