Скачать или смотреть 💡 Collections vs Collection in Java – Know the Difference

The Collections class in Java, found in the java.util package, provides a set of static utility methods that help in performing common operations on collections such as lists, sets, and maps. These methods simplify tasks like sorting, searching, and modifying collections. For example, the sort() method is used to sort a list in natural or custom order, while reverse() changes the order of elements in a list. The shuffle() method randomizes the list elements, and swap() allows exchanging the positions of two elements in a list. For searching operations, the binarySearch() method is used on sorted lists to find the position of a particular element efficiently. The class also includes methods like min() and max() to find the smallest or largest element in a collection, optionally using a custom comparator. Moreover, Collections offers methods like synchronizedList() or unmodifiableList() to make collections thread-safe or read-only, ensuring safety and immutability in concurrent programming. Overall, the Collections class serves as a toolbox of convenient methods that enhance productivity and code readability when dealing with Java collections.


In Java, the Collection interface is the root of the collection hierarchy and is part of the java.util package. It defines the basic methods that all collection types (like List, Set, Queue) must implement. These methods are used to add, remove, search, and manipulate elements in a collection. Unlike the Collections class, which provides utility methods, the Collection interface defines the core behavior of collection objects.

Here is a description of the commonly used Collection interface methods:
Common Collection Methods (in paragraph form)
The Collection interface provides several essential methods to work with groups of objects in Java. The add(E e) method is used to insert an element into the collection, while addAll() adds all elements from another collection. To remove elements, remove(Object o) deletes a single instance, and removeAll(Collection ) deletes all elements that exist in another collection. The clear() method empties the entire collection. To check whether an element or a set of elements exist, you can use contains(Object o) and containsAll(Collection). The method size() returns the number of elements, and isEmpty() checks whether the collection has no elements. For iterating through elements, the iterator() method provides an Iterator object. The toArray() method can be used to convert the collection into an array. Additionally, retainAll(Collection) retains only those elements that are also contained in the specified collection, effectively performing an intersection. These methods provide a foundation for all collection classes in Java, offering a unified way to interact with various types of data structures.