Collection Helper

This page consists of brief explanation and sample usages of the methods in CollectionHelper. You can see more details on each method by clicking on each hyperlinked method name.

Table of Contents

• addToList
• findInCollection
• forEach
• isEmpty(Collection)
• isEmpty(Map)
• isInCollection
• isInEnumSet
• isNotEmpty(Collection)
• isNotEmpty(Map)
• sanitize(Collection)
• sanitize(Map)
• sizeOf
• toList
• toSet

addToList

Adds the given element(s) to the given list. Initiates a new ArrayList if the list is null.

List<String> validOrderIds = null;
for (Order validOrder : validOrders) {
  validOrderIds.add(validOrder.getOrderId());
}

vs

List<String> validOrderIds = null;
for (Order validOrder : validOrders) {
  addToList(validOrderIds, validOrder.getOrderId());
}

---

findInCollection

Finds the first element in the given collection that satisfies the given predicate.

for (Order order : orders) {
  if (someOrderId.equals(order.getOrderId())) {
    order.setExpired(true);
  }
}

vs

Order order = findInCollection(orders, e - someOrderId.equals(e.getOrderId()));
doIfNotNull(order, e -> e.setExpired(true);

---

forEach

Executes the given function on the given collection.

if (orders != null) {
  orders.forEach(order -> {
    order.setExpired(true);
    order.setTotalAmount(order.getQuantity() * order.getAmount());
  });
}

vs

forEach(orders, order -> {
    order.setExpired(true);
    order.setTotalAmount(order.getQuantity() * order.getAmount());
  });
});

---

isEmpty (Collection)

Checks whether the given collection is empty.

if (order.getOrderItems() == null || order.getOrderItems().isEmpty()) {
  ...
}

vs

if (isEmpty(order.getOrderItems()) {
  ...
}

---

isEmpty (Map)

if (someMap == null || someMap.isEmpty()) {
  ...
}

vs

if (isEmpty(someMap)) {
  ...
}

---

isInCollection

Determines whether the specified element is in the given collection. Comparison is done by invoking .equals() on the element and all the elements inside the collection.

SomeClass targetObj;
for (SomeClass sc : someCollection) {
  if (sc.equals(targetObj)) {
     return true;
  }
}

vs

SomeClass targetObj;
return isInCollection(targetObj, someCollection);

---

isInEnumSet

Determines whether the specified enum is in the given EnumSet. Comparison is done by invoking .equals() on the enum and all the elements inside the EnumSet.

EnumSet.of(OrderType.RETAIL, OrderType.FLIGHT).contains(OrderType.FLIGHT);

vs

isInEnumSet(OrderType.FLIGHT, OrderType.RETAIL, OrderType.FLIGHT);

---

isNotEmpty (Collection)

Negation of isEmpty

---

isNotEmpty (Map)

Negation of isEmpty

---

sanitize (Collection)

Removes null elements from the collection. Given a list

List<String> list = new ArrayList<>();
list.add("someString1");
list.add(null);
list.add("someString2");

Removing null elements from the list would look like this:

if (isNotEmpty(list) {
  list.removeIf(Objects:isNull);
}

We can use sanitize instead to make it more readable:

sanitize(list);

---

sanitize (Map)

Removes elements with either null key or null value. Given a map:

Map<String, String> map = new HashMap<>();
map.put(null, "someValue1");
map.put("someKey2", "someValue2");
map.put("someKey3", null);

Doing the said operation would look like this:

if (map != null) {
  Iterator<Entry<String, String>> itr = map.entrySet().iterator();
  while (itr.hasNext()) {
    Entry<String, String> e = itr.next();
    if (e.getKey() == null || e.getValue() == null) {
      itr.remove();
    }
  }
}

We can use sanitize instead:

sanitize(map);

---

sizeOf

Simply returns the size of the collection.

int listSize = 0;
if (list != null) {
  listSize = list.size();
}

vs

int listSize = sizeOf(list);

---

toList

Creates a new ArrayList and populates it with the specified elements.

List<String> validIds = new ArrayList<>();
validIds.add("id1");
validIds.add("id2");
validIds.add(null); // validIds has 3 elements (including 1 null element)

vs

List<String> validIds = toList("id1", "id2", null); // validIds has 2 elements

---

toSet

Creates a new HashSet and populates it with the specified elements.

Set<String> validIds = new HashSet<>();
validIds.add("id1");
validIds.add("id2");
validIds.add(null); // validIds has 3 elements (including 1 null element)

vs

Set<String> validIds = toSet("id1", "id2", null); //validIds now has 2 elements