Java Collections Overview

ArrayList

• add(E e): Adds an element to the end of the list.
• get(int index): Retrieves the element at the specified index.
• remove(int index): Removes the element at the specified index.
• size(): Returns the number of elements in the list.
• isEmpty(): Checks if the list is empty.
• clear(): Removes all elements from the list.
• Sorting:
  • sort(Comparator<? super E> c): Sorts this list according to the order induced by the specified comparator.

LinkedList

• add(E e): Adds an element to the end of the list.
• addFirst(E e), addLast(E e): Adds an element to the beginning or end of the list.
• get(int index): Retrieves the element at the specified index.
• remove(int index): Removes the element at the specified index.
• size(): Returns the number of elements in the list.
• isEmpty(): Checks if the list is empty.
• clear(): Removes all elements from the list.
• Sorting:
  • sort(Comparator<? super E> c): Sorts this list according to the order induced by the specified comparator.

HashSet

• add(E e): Adds the specified element to the set if it is not already present.
• contains(Object o): Returns true if this set contains the specified element.
• remove(Object o): Removes the specified element from the set if it is present.
• size(): Returns the number of elements in the set.
• isEmpty(): Checks if the set is empty.
• clear(): Removes all elements from the set.

HashMap

• put(K key, V value): Associates the specified value with the specified key in the map.
• get(Object key): Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
• containsKey(Object key): Returns true if this map contains a mapping for the specified key.
• containsValue(Object value): Returns true if this map maps one or more keys to the specified value.
• remove(Object key): Removes the mapping for the specified key from the map if present.
• size(): Returns the number of key-value mappings in the map.
• isEmpty(): Checks if the map is empty.
• clear(): Removes all mappings from the map.
• Sorting:
  • Sorting is not directly applicable to HashMap as it's based on key-value pairs.

TreeSet

• add(E e): Adds the specified element to the set if it is not already present.
• contains(Object o): Returns true if this set contains the specified element.
• remove(Object o): Removes the specified element from the set if it is present.
• size(): Returns the number of elements in the set.
• isEmpty(): Checks if the set is empty.
• clear(): Removes all elements from the set.
• first(): Returns the first (lowest) element currently in the set.
• last(): Returns the last (highest) element currently in the set.

TreeMap

• put(K key, V value): Associates the specified value with the specified key in the map.
• get(Object key): Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
• containsKey(Object key): Returns true if this map contains a mapping for the specified key.
• containsValue(Object value): Returns true if this map maps one or more keys to the specified value.
• remove(Object key): Removes the mapping for the specified key from the map if present.
• size(): Returns the number of key-value mappings in the map.
• isEmpty(): Checks if the map is empty.
• clear(): Removes all mappings from the map.
• firstKey(): Returns the first (lowest) key currently in the map.
• lastKey(): Returns the last (highest) key currently in the map.
• Sorting:
  • Sorting is not directly applicable to TreeMap as it's based on key-value pairs.

PriorityQueue

• add(E e): Inserts the specified element into this priority queue.
• peek(): Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
• poll(): Retrieves and removes the head of this queue, or returns null if this queue is empty.
• size(): Returns the number of elements in the priority queue.
• isEmpty(): Checks if the priority queue is empty.
• clear(): Removes all elements from the priority queue.
• Sorting:
  • Priority queue sorts elements based on their natural ordering or the ordering specified by the provided comparator during initialization.