Question

Provide two page paper describing about Array list and operations & Iterators with very suitable examples.

Answer 1

ArrayList is based on Array data structure and implementes List interface. ArrayList is a resizable-array.

Array has fixed length. If the array is full you can't add more elements in it. To overcome this problem, arrayList is used. It can dynamically grow with no size limit. So it is called resizable array.

• It has duplicate elements also.
• It implements List interface and inherits AbstractList class
• It maintain insertion order
• It allows random access just like array

syntax of class ArrayList :
public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, Serializable

You can defined arrayList as :
ArrayList<Integer> arrList = new ArrayList<Integer>();
It will create a empty arrayList named arrList.

Basic operations on arrayList :

• void add(E e) - It will apppend e at the end of the list.

For e.g.
   arrList.add(5)
   arrList.add(10)
It will add 5 and 10 in the arrList
Thus, when you print arrList it will give output as [5, 10]

• E remove(int index) - It will remove the element present at that index.

For e.g.
   arrList.remove(1)
At index 1, we have 10. So it will be removed.
Thus, when you print arrList it will give output as [5]

• boolean isEmpty() - If the list is empty, it will return true, false otherwise.

For e.g.
   arrList.isEmpty()
It will return false as we have one element in the arrList.

• E get(int index) - It will return the element placed at given index

For e.g.
   arrList.get(0)
It will return 5, as at index 0, we have 5

• int indexOf(Object o) - It will return the index of the given object and -1 if the object is not present in the given arrayList

For e.g.
   arrList.indexOf(5)
It will return 0, as at index 0, we have 5

• void clear() - It will remove all the elements from given arrayList

For e.g.
   arrList.clear()
Now, arrList becomes null

• E set(int index, E element) - It will add given element at given index

For e.g.
   arrList.set(0,10)
It will add 10 at 0th position.

• int size() - It will return the number of elements present in the list

For e.g.
   arrList.size()
It will return 1 as we have only one element in arrList

Iterators :

To iterate a arrayList, we have iterator() method

Iterator iterator()

No any parameters are needed in this method. It returns an iterator over the elements presents in the list.

See given code snippet :

ArrayList<String>arrlist = new ArrayList<String>();  //It will create arrayList of string type
//adds an elements in the list
arrlist.add("abc");  
arrlist.add("def");  
arrlist.add("ghi");  
arrlist.add("jkl");  
 
System.out.println(arrlist);    // [abc, def, ghi, jkl]  

//To initialize iterator of string type on arrlist  
Iterator<String> iterator = arrlist.iterator();  
while (iterator.hasNext())  
{  
        String i = iterator.next();  
        System.out.println(i);    
}  

In each iteration, it will print one element of an arrlist

In above example,
hasNext() method is used to loop through whole arrlist

next() will return the next element

You can also use for loop to iterate an arrayList same as below

    for (int i : arrlist) {
      System.out.println(i);
    }