org.apache.mahout.math.function

## Interface DoubleComparator

• `public interface DoubleComparator`
A comparison function which imposes a total ordering on some collection of elements. Comparators can be passed to a sort method (such as org.apache.mahout.math.Sorting.quickSort) to allow precise control over the sort order.

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. In order for the data structure to serialize successfully, the comparator (if provided) must implement Serializable.

`Comparator`, `Sorting`
• ### Method Summary

All Methods
Modifier and Type Method and Description
`int` ```compare(double o1, double o2)```
Compares its two arguments for order.
`boolean` `equals(Object obj)`
Indicates whether some other object is "equal to" this Comparator.
• ### Method Detail

• #### compare

```int compare(double o1,
double 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 all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.)

The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0.

Finally, the implementer must ensure that compare(x, y)==0 implies that sgn(compare(x, z))==sgn(compare(y, z)) for all z.

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

`boolean equals(Object obj)`
Indicates whether some other object is "equal to" this Comparator. This method must obey the general contract of Object.equals(Object). Additionally, this method can return true only if the specified Object is also a comparator and it imposes the same ordering as this comparator. Thus, `comp1.equals(comp2)` implies that sgn(comp1.compare(o1, o2))==sgn(comp2.compare(o1, o2)) for every element o1 and o2.

Note that it is always safe not to override Object.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.

Overrides:
`equals` in class `Object`
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.
`Object.hashCode()`