What is ArrayList?ArrayList is a class in the Java which is present in the java.util package.
ArrayList class implements the List interface and inherits the AbstractList class.
ArrayList capacity grows automatically. ArrayList is created with an
initial size of 10, although we can
change it’s initial capacity.
It allows duplicate
elements.
Insertion order is
preserved in an ArrayList.
ArrayList allows us to random access.
ArrayList does not use with primitives like int, char, float etc. ArrayList uses with Wrapper classes.
ArrayList in Java is an alternate to vector in c++.
Difference between an Array and an ArrayList in Java:-
The main difference between of an Array and an ArrayList is that, the size of the array can not be grow or shrink at run time. while the size of an ArrayList can grow or shrink at run time. It means that an Array is static by nature and an ArrayList is dynamic by nature.
Constructors of ArrayList:-
| | Constructors and it's description |
| 1. | ArrayList( ) It is used to create an empty ArrayList with an initial size of 10. |
| 2. | ArrayList(int c) It is used to create an ArrayList with the specified capacity c. |
| 3. | ArrayList(Collection x) It is used to create an ArrayList initialized with the elements of the collection x. |
Methods of ArrayList:-
| | Methods and it's description |
| 1. | void add(int i, Object e) It is used to insert an specified element e at the specified position index i in a list. |
| 2. | boolean add(Object e) It is used to append the specified element e to the end of a list. |
| 3. | boolean addAll(Collection c) It is used to append all of the elements in the specified collection c to the end of the list, in the order that they are returned by the specified collection's iterator. |
| 4. | boolean addAll(int i, Collection c) It is used to insert all of the elements in the specified collection c, starting at the specified position i. |
| 5. | void clear( ) It is used to remove all of the elements from the ArrayList. |
| 6. | Object clone( ) It returns a shallow copy of this ArrayList. |
| 7. | boolean contains(Object o) It returns true if the ArrayList contains the specified element o, otherwise returns false. |
| 8. | void ensureCapacity(int capacity) It is used to increase the capacity of the ArrayList instance. |
| 9. | Object get(int index) It returns the element at the specified index position in the ArrayList. |
| 10. | int indexOf(Object o) It returns the index position in the ArrayList of the first occurrence of the specified element o, or -1 if the List does not contain this element. |
| 11. | int lastIndexOf(Object o) It returns the index position in the ArrayList of the last occurrence of the specified element o, or -1 if the List does not contain this element. |
| 12. | Object remove(int x) It is used to remove the element at the specified position x in the list. |
| 13. | protected void removeRange(int fromIndex, int toIndex) It is used to remove all of the elements from the List whose index is between fromIndex to toIndex. |
| 14. | Object set(int index, Object element) It is used to replace the element at the specified index position in the ArrayList with the specified element. |
| 15. | int size( ) It is used to find the number of elements in the list. |
| 16. | Object[ ] toArray( ) It returns an array containing all of the elements in the ArrayList in the correct order. |
| 17. | boolean isEmpty( ) It returns true if the ArrayList is empty, otherwise false. |
| 18. | void trimToSize( ) It is used to trim the capacity of the ArrayList instance to be the list's current size. |
| 19. | void sort(Collection<?> c ) It is used to sort all the elements of the ArrayList. |
| 20. | boolean removeAll(Collection<?> c) It is used to remove all the elements of the ArrayList. |
Creation of ArrayList:-
ArrayList can be created in two ways:-
1. Type unsafe
2. Type safe
Type Unsafe ArrayList:-
It can be created as shown below-
ArrayList list=new ArrayList( );
Although they are easier to create but
we cannot check what kind of data we are adding in the ArrayList.
for example:-
1. list.add("Naman");
2. list.add(20);
3. list.add(true);
4. list.add(25.5);
All the above lines will successfully compile and run.
Type Safe ArrayList:-
It can be created as shown below-
ArrayList<String> list=new ArrayList<String>( );
The < > are called diamond operator in Java and they tell the compiler to
only allow us to add String values in the ArrayList.
Any other type of
value cannot be added in the ArrayList and if we try to do so, the compiler
will generate syntax error.
for example:-
1. list.add("Naman"); // correct
2. list.add(20); // wrong
3. list.add(true); // wrong
4. list.add(25.5); // wrong
Inserting elements in ArrayList:-
To insert element in the ArrayList, we have to call the method add( ).
This method has two versions:-
Prototype of the method add( ):-
1. public boolean add(Object):- The first method
accepts an Object as argument and adds that Object at the end of the ArrayList.
2. public void add(int, Object):- The second method
accepts an index number as well as an Object as argument and adds the Object at
the specified index. If index is out of
range then it throws the exception IndexOutOfBoundsException.
for example:-
ArrayList<String> list=new ArrayList<String>( );
1. list.add("India");
2. list.add(0, "England");
Retrieving elements of ArrayList:-
To retrieve an elements from the ArrayList, we have to call the method get( ).
Prototype of the method get( ):-
1. public Object get(int index):- This method accepts an index number as argument and
returns the element at that position.
If index is out of range then it throws the exception IndexOutOfBoundsException.
for example:-
ArrayList<String> list=new ArrayList<String>( );
list.add("India");
list.add("Japan");
String s=list.get(0);
String p=list.get(1);
System.out.println(s); // will show India
System.out.println(p); // will show Japan
Checking size of an ArrayList:-
Size of an ArrayList means total number of elements currently present in an ArrayList.
To retrieve size of an ArrayList, we have a method called size( ), whose prototype is-
public int size(int index)
for example:-
ArrayList<String> list=new ArrayList<String>( );
list.add("India");
list.add("England");
int x=list.size();
System.out.print(x); // will get 2
Searching an element in an ArrayList:-
Sometimes we need to check whether an element exists in an ArrayList or not.
For this purpose we can use contains( ) method of Java, whose prototype is-
public boolean contains(Object):- contains( ) method takes type of object defined in the ArrayList creation and returns true if this list contains the specified element.
for example:-
ArrayList<String> list=new ArrayList<String>( );
list.add("Indore");
list.add("Bhopal");
boolean x=list.contains("Indore");
boolean y=list.contains("Gwalior");
System.out.print(x); // will get true
System.out.print(y); // will get false
Another way of Searching an element in an ArrayList:-
we can also use indexOf() method of ArrayList in Java to find out index of a particular object or it returns -1 if the List does not contains this element.
for example:-
ArrayList<String> list=new ArrayList<String>( );
list.add("Indore");
list.add("Bhopal");
int x=list.indexOf("Indore");
int y=list.indexOf("Gwalior");
System.out.print(x); // will get 0
System.out.print(y); // will get -1
Removing an element from an ArrayList:-
There are two ways to remove any element from an ArrayList in Java. The method to be called is remove( ).
It has two versions:-
1. public Object remove(int)
2. public boolean remove(Object)
We can either remove an element based on its index or by
providing object itself.
for example:-
ArrayList<String> list=new ArrayList<String>( );
list.add("Indore");
list.add("Bhopal");
list.remove(0);
list.remove("Bhopal");
System.out.print(list.size()); // will get 0
Changing an element in an ArrayList:-
To change or modify element in an ArrayList, we have to call the method set( ).
public Object set(int, Object):- It replaces the element at the specified index position in the ArrayList with the specified element.
for example:-
ArrayList<String> list=new ArrayList<String>( );
list.add("Indore");
list.add("Bhopal");
list.set(0,"Gwalior");
System.out.print(list.get(0)); // will get Gwalior
System.out.print(list.get(1)); // will get Bhopal
Sorting of an element in an ArrayList:-
The Java language provides us
predefined sorting functions/methods to sort the elements of collections like ArrayList.
Thus, we do not have
to write our own logic for sorting these collections.
This is done using a
class called “Collections” in the package java.util which contains a
static method called sort(
) which can sort an ArrayList.
The prototype of the
method is:-
public static
void sort(List L)
This method accepts a
List as argument and sorts it’s elements in natural order.
What is natural order?
Natural order means the default sorting order which is as follows:-
1) If
the List consists of String elements, it will be sorted into alphabetical order.
2) If it contains Integers , it will be sorted
in numeric order.
3) If it consists
of Date elements, it will be sorted
into chronological order.
Example:-
Ranking of top 5
teams given by ICC for ODI
in 2020 is as follows:
1- England
2- India
3- New Zealand
4- South Africa
5- Australia
Write a program to do the following:-
1. Accept names of these
5 teams and store them in the ArrayList.
2. prints size of an ArrayList.
3. Now ask the user to
input a team name and search and print it’s ranking. If the team name is not
found then print the message Team not found.
4. And at last sort the element of an ArrayList.
Solution:-
Output:-
What is a custom ArrayList?
A custom ArrayList is an ArrayList which can hold objects of programmer defined classes.
For example, suppose we have a class called Employee and we want to store Employee objects in an ArrayList then such an ArrayList will be called a custom ArrayList.
How do we create a custom ArrayList?
To create a custom ArrayList, we use the following syntax-
ArrayList <name of our class> refName= new ArrayList< >( );
for example:-
ArrayList <Employee> emp= new ArrayList<Employee>( );
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