Collections Interface

The Collections Framework in Java provides a unified architecture to represent and manipulate collections like lists, sets, queues, and maps.

It’s the base interface for all types of collections (List, Set, Queue…). Key Methods in Collection<E>

public boolean add(E e)
public boolean addAll(Collection<?> c)
public boolean remove(Object element)
public boolean removeAll(Collection<?> c)

public boolean contains(Object element)
public boolean containsAll(Collection<?> c)

//Other utility methods
public int size() // list.size();
public void clear() // clears a collection
public boolean isEmpty() //Checks if collection is empty
public Iterator iterator() // returns a iterator
public Object[] toArray()
Collections.sort(al);  
Collections.sort(al,Collections.reverseOrder());  
Collections.reverse(al);