Java ArrayList

Java ArrayList:

Class Synatx:

java.lang.Object
     java.util.AbstractCollection
          java.util.AbstractList
               java.util.ArrayList

• ArrayList is a part of collection framework.
• The ArrayList class is a resizable array, which can be found in the java.util package.
• Java ArrayList class uses a dynamic array for storing the elements. 
• The difference between a built-in array and an ArrayList:
• In, built-in array, the size of an array cannot be modified. 
• While in ArrayList, elements can be added and removed whenever you want. 
• Import Package: import java.util.ArrayList

Syntax: 

ArrayList = new ArrayList();

Example of string: 

ArrayList students = new ArrayList();

Example of Integer:

ArrayList myNumbers = new ArrayList();

Constructors in ArrayList:

• ArrayList(): This constructor is used to build an empty array list
• ArrayList(Collection c):  This constructor is used to build an array list initialized with the elements from collection c
• ArrayList(int capacity):  This constructor is used to build an array list with initial capacity being specified

Advantages:

• Java ArrayList class can contain duplicate elements.
• Java ArrayList class maintains insertion order.
• Java ArrayList class is non synchronized.
• Java ArrayList allows random access because array works at the index basis.
• In Java ArrayList class, manipulation is slow because a lot of shifting needs to occur if any element is removed from the array list.

Methods:

• How to add Items:
• For example, to add elements to the ArrayList, use the add() method:
• Syntax: Object-name.add(string);
• Example: students.add("Sarthak");
• Example: myNumbers .add(7);
• How to find size of ArrayList
• To find out how many elements an ArrayList have, use the size method:
• Syntax: Object-name.size();
• Example: students.size();
• Example: myNumbers .size();
• How to access an Item:
• To access single items:
• To access an element in the ArrayList, use the get() method and refer to the index number:
• Syntax: Object-name.get(index);
• Example: System.out.println(students.get(0));
• Example: System.out.println(myNumbers.get(0));
• To access multiple items using for loop:
• Loop through the elements of an ArrayList with a for loop, and use the size() method to specify how many times the loop should run:
• Example: 

                                     for (int i = 0; i < students.size(); i++) {

                                                 System.out.println(students.get(i));

                                         }

• Example: 

                                     for (int i = 0; i < myNumbers.size(); i++) {

                                                 System.out.println(myNumbers.get(i));

                                         }

• To access multiple items using for each loop:
• Example:

                                         for (String i : students ) {

                                                      System.out.println(i);

                                              }

• Example:

                                         for (Integer i : myNumbers) {

                                                      System.out.println(i);

                                              }

• How to change an Item:
• To modify an element, use the set() method and refer to the index number:
• Syntax: Object-name.set(index,string);
• Example: students.set(0, "Badal");
• Example: myNumbers.set(0, 11);
• How to remove an Item
• Remove Single Item
• To remove an element, use the remove() method and refer to the index number:
• Syntax: Object-name.remove(index);
• Example: students.remove(0);
• Example: myNumbers.remove(0);
• Remove all items
• To remove all the elements in the ArrayList, use the clear() method:
• Syntax: Object-name.clear();
• Example: students.clear();
• Example: myNumbers.clear();
• Other Methods of Java ArrayList:
• 1. boolean isEmpty() : It returns true if the list is empty, otherwise false.
• 2. boolean contains(Object o) : It returns true if the list contains the specified element
• 3. int indexOf(Object o) : It is used to return the index in this list of the first occurrence of the specified element, or -1 if the List does not contain this element.