ArrayList (List) Methods

Question 1

Declaring a ArrayList

Answer 1

ArrayList arraylist = new ArrayList();

Question 2

Adding an Item at the List

Answer 2

arraylist.add(“Element”);

Question 3

Adding an element at a particular position of ArrayList

Answer 3

arraylist.add(3,Element);

Question 4

Adding all element of a list to the end of the ArrayList

Answer 4

arraylist.addall(list-name);

Question 5

Adding a list to a particular position of ArrayList

Answer 5

arraylist.addall(2,list-name);

Question 6

Adding a ArrayList to Another ArrayList

Answer 6

arraylist-first.append(arraylist-second);

Question 7

Removing an Item from the List (Any Element)

Answer 7

arraylist.remove(“Element”);

Question 8

Removing an Item from a particular position of an ArrayList

Answer 8

arraylist.remove(2);

Question 9

Retrieving an Item from an ArrayList based on the Index

Answer 9

arraylist.get(5)

Question 10

Retrieving a sublist from an ArrayList <i>Based on Index</i>

Answer 10

arraylist.sublist(2,5)

Question 11

Retrieving Index of an Item

Answer 11

arraylist.indexOf(“Element”);

Question 12

Retrieving Last Index of an Item

Answer 12

arraylist.lastIndexOf(“Element”);

Question 13

Size of an ArrayList

Answer 13

arraylist.size();

Question 14

Sorting an ArrayList

Answer 14

Collection.sort(arraylist);

Question 15

Reverse Sorting an Array List

Answer 15

Method 1 : Collection.reverse(arraylist);

Method 2 : Collection.sort (arraylist,Collection.reverseOrder());

Question 16

Iterating over an ArrayList (Method 1: For Loop)

Answer 16

Method 1 - FOR LOOP
for (int counter = 0; counter < arraylist.size(); counter++) {
System.out.println(arraylist.get(counter));
}

Question 17

Iterating over an ArrayList (Method 2: While Loop)

Answer 17

Method 2 - WHILE LOOP 
int count = 0; 		
while (arraylist.size() > count) {
    System.out.println(arraylist.get(count));
    count++;
     }

Question 18

Iterating over an ArrayList (Method 3: ITERATOR)

Answer 18

Method 3 - ITERATOR
Iterator iterator = arraylist.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}

Question 19

Is this item there in the ArrayList?

Answer 19

arraylist.contains(“Element”);

Question 20

Swapping elements in an arraylist

Answer 20

Collection.swap(arraylist,1,4);

Question 21

Difference between Array and ArrayList?

Answer 21

Contains:
Arrays can contain primitive or Objects
ArrayList can contain only Objects.

Size:
Arrays are fixed size
ArrayList size is dynamic.

Feature
Arrays doesn’t provide a lot of features like ArrayList, such as addAll, removeAll, iterator Set implementations: HashSet, LinkedHashSet, TreeSet etc.

Question 22

When will you use Array over ArrayList?

Answer 22

Although ArrayList is the obvious choice when we work on list, there are few times when array are good to use.

If the size of list is fixed and mostly used to store and traverse them.
For list of primitive data types, although Collections use autoboxing to reduce the coding effort but still it makes them slow when working on fixed size primitive data types.
If you are working on fixed multi-dimensional situation, using [][] is far more easier than List>