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ArrayList.md

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ArrayList

ArrayList is a part of collection framework and is present in java.util package. It provides us with dynamic arrays in Java. Though, it may be slower than standard arrays but can be helpful in programs where lots of manipulation in the array is needed.

NOTE: ArrayList is the BEST choice for retrieval operations while WORST choice for inserting values in some position of ArrayList

Imp Properties of ArrayList.

ArrayList Constructors

To create ArrayList with capacity initialCapacity

To convert a Collection object into an ArrayList, it creates an ArrayList from the objects of the Collection c

Methods of ArrayList

  • boolean add(Object o)

    Appends the specified element to the end of this ArrayList.

  • void add(int index, Object element)

    Inserts the specified element at the specified position in this ArrayList.

       ArrayList<String> al = new ArrayList<>(); 
   al.add("Geeks"); 
   al.add("Geeks"); 
   al.add(1, "For");
   System.out.println(al); // [Geeks, For, Geeks]

  • boolean addAll(Collection c)

    Appends all of the elements in the specified Collection to the end of this this ArrayList, in the order that they are returned by the specified Collection's Iterator.

  • boolean addAll(int index, Collection c)

    Inserts all of the elements in the specified Collection into this ArrayList, starting at the specified position.

  • void clear()

    Removes all of the elements from this ArrayList.

  • Object clone()

    Returns a shallow copy of this ArrayList.

  • boolean contains(Object elem)

    Returns true if this ArrayList contains the specified element.

  • int indexOf(Object elem)

    Searches for the first occurence of the given argument, testing for equality using the equals method.

  • boolean isEmpty()

    Tests if this ArrayList has no components.

  • int lastIndexOf(Object elem)

    Returns the index of the last occurrence of the specified object in this ArrayList.

  • Object remove(int index)

    Removes the element at the specified position in this ArrayList.

       ArrayList<String> al = new ArrayList<>(); 

   al.add("Geeks"); 
   al.add("Geeks"); 
   al.add(1, "For"); 

   System.out.println("Initial ArrayList " + al); 
   //Initial ArrayList [Geeks, For, Geeks]

   al.remove(1); 

   System.out.println("After the Index Removal " + al); 
   //After the Index Removal [Geeks, Geeks]
   al.remove("Geeks"); 

    System.out.println("After the Object Removal " + al);
    //After the Object Removal [Geeks]

  • Object set(int index, Object element)

    Replaces the element at the specified position in this ArrayList with the specified element.

       ArrayList<String> al = new ArrayList<>(); 

   al.add("Geeks"); 
   al.add("Geeks"); 
   al.add(1, "Geeks"); 
   
   System.out.println("Initial ArrayList " + al); //Initial ArrayList [Geeks, Geeks, Geeks]

   al.set(1, "For"); 

   System.out.println("Updated ArrayList " + al); //Updated ArrayList [Geeks, For, Geeks]

  • Object get(int index)

    Returns the element at the specified position in this ArrayList.

  • int size()

    Returns the number of components in this ArrayList.

       ArrayList<String> al  = new ArrayList<>(); 

   al.add("Geeks"); 
   al.add("Geeks"); 
   al.add(1, "For"); 

      // Using the Get method and the 
      // for loop 
   for (int i = 0; i < al.size(); i++)

      System.out.print(al.get(i) + " "); 

   System.out.println(); 

   // Using the for each loop 
   for (String str : al) 
          System.out.print(str + " "); 
  }