Java ArrayList class
- Java
ArrayList class uses a dynamic array for storing the elements.It extends
AbstractList class and implements List interface.
- 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 be occurred if any element is removed from the array list.
Java Non-generic Vs Generic Collection
Java collection framework was non-generic before
JDK 1.5. Since 1.5, it is generic.
Java new generic collection allows you to have
only one type of object in collection. Now it is type safe so typecasting is
not required at run time.
Let's see the old non-generic example of
creating java collection.
1. ArrayList al=new ArrayList();//creating old non-generic arraylist
Let's see the new generic example of creating
java collection.
1. ArrayList<String> al=new ArrayList<String>();//creating new generic arraylist
In generic collection, we specify the type in
angular braces. Now ArrayList is forced to have only specified type of objects
in it. If you try to add another type of object, it gives compile time
error.
Example of Java ArrayList class
1. import java.util.*;
2. class TestCollection1{
3. public static void main(String args[]){
4.
5. ArrayList<String> al=new ArrayList<String>();//creating arraylist
6. al.add("Ravi");//adding object in arraylist
7. al.add("Vijay");
8. al.add("Ravi");
9. al.add("Ajay");
10.
11. Iterator itr=al.iterator();//getting Iterator from arraylist to traverse elements
12. while(itr.hasNext()){
13. System.out.println(itr.next());
14. }
15. }
16. }
Ravi
Vijay
Ravi
Ajay
Two ways to iterate the elements of collection
in java
- By
Iterator interface.
- By
for-each loop.
In the above example, we have seen traversing
ArrayList by Iterator. Let's see the example to traverse ArrayList elements
using for-each loop.
Iterating the elements of Collection by
for-each loop
1. import java.util.*;
2. class TestCollection2{
3. public static void main(String args[]){
4. ArrayList<String> al=new ArrayList<String>();
5. al.add("Ravi");
6. al.add("Vijay");
7. al.add("Ravi");
8. al.add("Ajay");
9. for(String obj:al)
10. System.out.println(obj);
11. }
12. }
Ravi
Vijay
Ravi
Ajay
User-defined class objects in Java ArrayList
1. class Student{
2. int rollno;
3. String name;
4. int age;
5. Student(int rollno,String name,int age){
6. this.rollno=rollno;
7. this.name=name;
8. this.age=age;
9. }
10. }
1. import java.util.*;
2. public class TestCollection3{
3. public static void main(String args[]){
4. //Creating user-defined class objects
5. Student s1=new Student(101,"Sonoo",23);
6. Student s2=new Student(102,"Ravi",21);
7. Student s2=new Student(103,"Hanumat",25);
8.
9. ArrayList<Student> al=new ArrayList<Student>();//creating arraylist
10. al.add(s1);//adding Student class object
11. al.add(s2);
12. al.add(s3);
13.
14. Iterator itr=al.iterator();
15. //traversing elements of ArrayList object
16. while(itr.hasNext()){
17. Student st=(Student)itr.next();
18. System.out.println(st.rollno+" "+st.name+" "+st.age);
19. }
20. }
21. }
101 Sonoo 23
102 Ravi 21
103 Hanumat 25
Example of addAll(Collection c) method
1. import java.util.*;
2. class TestCollection4{
3. public static void main(String args[]){
4.
5. ArrayList<String> al=new ArrayList<String>();
6. al.add("Ravi");
7. al.add("Vijay");
8. al.add("Ajay");
9.
10. ArrayList<String> al2=new ArrayList<String>();
11. al2.add("Sonoo");
12. al2.add("Hanumat");
13.
14. al.addAll(al2);
15.
16. Iterator itr=al.iterator();
17. while(itr.hasNext()){
18. System.out.println(itr.next());
19. }
20. }
21. }
Ravi
Vijay
Ajay
Sonoo
Hanumat
Example of removeAll(Collection c) method
1.
import java.util.*;
2.
class TestCollection5{
3.
public static void main(String args[]){
4.
5.
ArrayList<String> al=new ArrayList<String>();
6.
al.add("Ravi");
7.
al.add("Vijay");
8.
al.add("Ajay");
9.
10. ArrayList<String> al2=new ArrayList<String>();
11. al2.add("Ravi");
12. al2.add("Hanumat");
13.
14. al.removeAll(al2);
15.
16. System.out.println("iterating the elements after removing the elements of al2...");
17. Iterator itr=al.iterator();
18. while(itr.hasNext()){
19. System.out.println(itr.next());
20. }
21.
22. }
23. }
iterating the elements after removing
the elements of al2...
Vijay
Ajay
Example of retainAll(Collection c) method
1.
import java.util.*;
2.
class TestCollection6{
3.
public static void main(String args[]){
4.
ArrayList<String> al=new ArrayList<String>();
5.
al.add("Ravi");
6.
al.add("Vijay");
7.
al.add("Ajay");
8.
ArrayList<String> al2=new ArrayList<String>();
9.
al2.add("Ravi");
10. al2.add("Hanumat");
11.
12. al.retainAll(al2);
13.
14. System.out.println("iterating the elements after retaining the elements of al2...");
15. Iterator itr=al.iterator();
16. while(itr.hasNext()){
17. System.out.println(itr.next());
18. }
19. }
20. }
iterating the elements after retaining
the elements of al2...
Ravi
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