org.jutil.java.collections
Class Counter

java.lang.Object
  |
  +--org.jutil.java.collections.IntegerAccumulator
        |
        +--org.jutil.java.collections.Counter

All Implemented Interfaces:

CollectionOperator

public abstract class Counter

extends IntegerAccumulator

An IntegerAccumulator that counts the number of items in a collection that satisfies some criterion.

A convenience accumulator of collections that checks elements of a collection satisfy the criterion defined in public boolean criterion(Object element).

As with the accumulator, this class can best be used as an anonymous inner class, as shown below.

 int number = new Counter() {
                public boolean criterion(Object element) {
                  // criterion code
                }
              }.in(collection);
 

Version:

$Revision: 1.4 $

Author:

Marko van Dooren

Field Summary

static java.lang.String

CVS_REVISION

Constructor Summary

Counter()

Method Summary

int	accumulate(java.lang.Object element, int acc) also public behavior // If the element satisfies the criterion, acc + 1 is returned to // indicate 1 more element satisfies the criterion. // otherwise acc is returned. post criterion(element) == false ==> \result == acc; post criterion(element) == true ==> \result == acc + 1;
abstract boolean	criterion(java.lang.Object element) //As usual, criterion must be consistent with the semantics of equals post (\forall Object o1;; (\forall Object o2; o1.equals(o2); criterion(o1) == criterion(o2))); The criterion used to determine whether or not an element has to be counted.
int	initialAccumulator() also public behavior post \result == 0;

Methods inherited from class org.jutil.java.collections.IntegerAccumulator

in

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

CVS_REVISION

public static final java.lang.String CVS_REVISION

Constructor Detail

Counter

public Counter()

Method Detail

initialAccumulator

public int initialAccumulator()

also public behavior

post \result == 0;

Overrides:

initialAccumulator in class IntegerAccumulator

accumulate

public int accumulate(java.lang.Object element,
                      int acc)

also public behavior

// If the element satisfies the criterion, acc + 1 is returned to
// indicate 1 more element satisfies the criterion.
// otherwise acc is returned.
post criterion(element) == false ==> \result == acc;
post criterion(element) == true ==> \result == acc + 1;

Overrides:

accumulate in class IntegerAccumulator

Following copied from class: org.jutil.java.collections.IntegerAccumulator

Parameters:

element - The object the method will process and change the accumulator with.

acc - The accumulator for the accumulation. For the first element to be processed, the result of initialAccumulator is used. For the other elements, the result of this method applied on the previous element is used.

criterion

public abstract boolean criterion(java.lang.Object element)

//As usual, criterion must be consistent with the semantics of equals
post (\forall Object o1;;
(\forall Object o2; o1.equals(o2);
criterion(o1) == criterion(o2)));
The criterion used to determine whether or not an element has to be counted.