This document discusses utilities for working with collections and sets in Java, including checking for null/empty collections, performing set operations like union and intersection, filtering/transforming collections with predicates and transformers, and iterating over collections with closures. It provides examples of implementing these utilities with both imperative code and reusable predicates, transformers, and closures. The utilities allow for cleaner logic, testable code, and a more functional style.

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