Short preview on CollectionUtils, an Apache collection module.

1. CollectionUtils
Let me throw you for a loop

2. Null safety
if(collection!=null && !collection.isEmpty()) {
doSomthing();
}

3. Null Safety
CollectionUtils.isEmpty(collection);
CollectionUtils.isNotEmpty(collection);
MapUtils.isEmpty(map);
MapUtils.isNotEmpty(map);

4. Set operations

5. Set operations
Union
Collection union = new ArrayList(group1);
for (Object o : group1) {
if(!group2.contains(o)) {
union.add(o);
}
}
"
CollectionUtils.union(group1, group2);

6. Set operations
Intersection
Collection<Object> intersection = new ArrayList<>();
for (Object o : group1) {
if (group2.contains(o)) {
intersection.add(o);
}
}
for (Object o : group2) {
if (group1.contains(o)) {
intersection.add(o);
}
}
CollectionUtils.intersection(group1, group2);

7. Set operations
Disjunction
Collection<Object> disjunction = new ArrayList<>();
for (Object o : group1) {
if (!group2.contains(o)) {
disjunction.add(o);
}
}
for (Object o : group2) {
if (!group1.contains(o)) {
disjunction.add(o);
}
}
CollectionUtils.disjunction(group1, group2);

8. Set operations
Subtraction
Collection subtraction = new ArrayList<>(group1);
for (Object o : group1) {
if(group2.contains(o)) {
subtraction.remove(o);
}
}
CollectionUtils.subtract(group1, group2);

9. Cardinality
Object item = new Object();
int count = 0;
for (Object o : group1) {
if(o.equals(item)) {
++count;
}
}
CollectionUtils.cardinality(item, group1);
CollectionUtils.getCardinalityMap(group1);

10. The real deal
Predicates
Transformers
Closures

11. Predicate
Collection<Campaign> campaigns = getCampaigns();
Iterator<Campaign> campaignIterator = campaigns.iterator();
while (campaignIterator.hasNext()) {
if (campaignIterator.next().getExposureCount() > 0) {
campaignIterator.remove();
}
}

12. Predicate
private static class Campaign {
public static final Predicate<Campaign> EXPOSED = new
Predicate<Campaign>() {
@Override
public boolean evaluate(Campaign campaign) {
return campaign.getExposureCount() > 0;
}
};
private int exposureCount = 0;
public int getExposureCount() {
return exposureCount;
}
public void setExposureCount(int exposureCount) {
this.exposureCount = exposureCount;
}
}
12

13. Predicate
CollectionUtils.filter(campaigns, Campaign.EXPOSED);
CollectionUtils.select(campaigns, Campaign.EXPOSED);
CollectionUtils.selectRejected(campaigns, Campaign.EXPOSED);
CollectionUtils.countMatches(campaigns, Campaign.EXPOSED);
"
"
PredicateUtils.notPredicate(Campaign.EXPOSED);
PredicateUtils.instanceofPredicate(Campaign.class);
PredicateUtils.notNullPredicate();

14. Transformer
Collection<Campaign.Type> campaignTypes = new
ArrayList<>(campaigns.size());
for (Campaign campaign : campaigns) {
campaignTypes.add(campaign.getType());
}

15. Transformer
private static class Campaign {
public enum Type {
Sales,
Service,
Other
}
public static final Transformer<Campaign, Campaign.Type> TO_TYPE = new Transformer<Campaign,
Type>() {
@Override
public Type transform(Campaign campaign) {
return campaign.getType();
}
};
private Type type;
public Type getType() {
return type;
}
public void setType(Type type) {
this.type = type;
}
}

16. Transformer
CollectionUtils.collect(campaigns, Campaign.TO_TYPE);
TransformerUtils.invokerTransformer("getType"); //DO NOT USE

17. Closure
for (Campaign campaign : campaigns) {
campaign.setExposureCount(campaign.getExposureCount() + 1);
}

18. Closure
private static class Campaign {
public static final Closure<Campaign> INCREMENT_EXPOSURE = new
Closure<Campaign>() {
@Override
public void execute(Campaign input) {
++input.exposureCount;
}
};
private int exposureCount = 0;
public int getExposureCount() {
return exposureCount;
}
public void setExposureCount(int exposureCount) {
this.exposureCount = exposureCount;
}
}

19. Closure
CollectionUtils.forAllDo(campaigns, Campaign.INCREMENT_EXPOSURE);
ClosureUtils.chainedClosure(Campaign.INCREMENT_EXPOSURE,
Campaign.INCREMENT_EXPOSURE);

20. What I like about it:
Clean logic code
Testable code!!!
Reusable code
Smells like functional

21. Notes
Java 8 Lambda expressions gives a lot of it…
Be aware of anonymous functions