Collection Framework Java

• List

  • ArrayList

    • add() - O(n)
    • get()
    • addAll()
    • add(index, element)
    • remove(index) - O(n)
    • remove(Integer.valueOf(val))
    • clear() - completely removes all elements of the list(empties the list)
    • set(index, value) -O(1)
    • contains(element) - checks if element present in the array or not , return true or false - O(n)
    • size() - length of the list
    • for(Integer element: list){ System.out.println(“the element is: ”+element )}
    • Iterator it = list.iterator(); // helps in iterating for collection
      • while(it.hasNext()){ System.out.println(“iterator: ”+it.next())}

  • Stack

    • Stack st = new Stack<>();
    • st.push(“Pentium”)
    • st.peek() - element present at top
    • st.pop() - removes toppest element

  • LinkedList

    • Same functions as arrayList.

• Queue

  • LinkedList

    • Queue queue = new LinkedList<>();
    • queue.offer(12) - inserting elements in the queue
    • queue.poll() - returns first element that was inserted in the queue. we can print this element
    • queue.peek() - which element will be removed next
    • add() - throws exception in case of error… same as offer()
    • element() - throws exception in case of error… same as peek(), which returns null if no element found in queue
    • remove() - throws exception in case of error…. same as poll(), which returns null if no element found in queue

  • PriorityQueue

    • PriorityQueue pq = new PriorityQueue<>(); or Queue pq = new PriorityQueue<>();
    • same functions like earlier: offer(), peek(), poll(), etc., can be used as it is a part of queue.
    • after adding elements order is changed as min Heap is implemented and since priority is of smallest element therefore the smallest element is printed if we use poll()
    • To change priority to maximum element we can use comparator as follows:
      • PriorityQueue pq = new PriorityQueue<>(Comparator.reverseOrder());

  • ArrayDeque

    • Doubly ended queue
    • ArrayDeque add = new ArrayDeque<>();
    • same functions like earlier: offer(), peek(), poll(), etc., can be used as it is a part of queue. adds elements at last
    • adq.offerFirst() - insert element at the starting
    • adq.offerLast() - insert element at the end same as offer()
    • adq.peekFirst() - view the starting element same as peek()
    • adq.peekLast() - view the last element
    • adq.pollFirst() - removes element at the starting same as poll()
    • adq.pollLast() - removes element at the end

• Set

  • HashSet

    • follows set property that is no duplicates allowed
    • Set set = new HashSet<>();
    • set.add() - to add elements in the set
    • prints in a random order.
    • creates hash for each element in the set
    • set.remove(element) - to remove element from the set
    • set.contains(element) - tells if element is present in the set or not … return boolean
    • set.isEmpty() - to know if currently set is empty or not…. returns boolean
    • set.size() - tells the size or number of elements present in the set.
    • set.clear() - to clear set i.e. remove all elements from the set.
    • O(1)

  • LinkedHashSet

    • similar property as above
    • order remains same as inserted in the form of a linked list.

  • TreeSet

    • does everything in sorted from
    • Implementation over binary tree
    • ordered and sorted
    • O(log n)