Java Collections Framework:ArrayList-6

 

How to compare two ArrayList in Java


In this tutorial we will learn how to compare two ArrayList. We would be using contains() method for comparing two elements of different ArrayList.

public boolean contains(Object o)
It returns true if the list contains the Object o else it returns false.

Example:

In this example we have two ArrayList al1 and al2 of String type. We have compared these ArrayLists using contains() method and stored the comparison result in third ArrayList (al3 and al4).

package beginnersbook.com;
import java.util.ArrayList;
public class Details
{
     public static void main(String [] args)
     {
          ArrayList<String> al1= new ArrayList<String>();
          al1.add("hi");
          al1.add("How are you");
          al1.add("Good Morning");
          al1.add("bye");
          al1.add("Good night");

          ArrayList<String> al2= new ArrayList<String>();
          al2.add("Howdy");
          al2.add("Good Evening");
          al2.add("bye");
          al2.add("Good night");

          //Storing the comparison output in ArrayList<String>
          ArrayList<String> al3= new ArrayList<String>();
          for (String temp : al1)
              al3.add(al2.contains(temp) ? "Yes" : "No");
          System.out.println(al3);

          //Storing the comparison output in ArrayList<Integer>
          ArrayList<Integer> al4= new ArrayList<Integer>();
          for (String temp2 : al1)
               al4.add(al2.contains(temp2) ? 1 : 0);
          System.out.println(al4);
     }
}

Output:



[No, No, No, Yes, Yes]
[0, 0, 0, 1, 1]

What is the logic in above code?
If the first element of ArrayList al1 is present in al2 then ArrayList al3 would be having “Yes” and al4 would be having “1” However if the element is not present “No” would be stored in al3 and 0 would be in al4.

How to synchronize ArrayList in java with example



There are two ways to synchronize explicitly:

  1. Using Collections.synchronizedList() method
  2. Using thread-safe variant of ArrayList: CopyOnWriteArrayList

Example 1: Collections.synchronizedList() method for Synchronizing ArrayList

In this example we are using Collections.synchronizedList() method. The important point to note here is that iterator should be in synchronized block in this type of synchronization as shown in the below example.

package beginnersbook.com;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Collections;

public class Details {

   public static void main(String a[]){
       List<String> syncal = 
         Collections.synchronizedList(new ArrayList<String>());

       //Adding elements to synchronized ArrayList
       syncal.add("Pen");
       syncal.add("NoteBook");
       syncal.add("Ink");

       System.out.println("Iterating synchronized ArrayList:");
       synchronized(syncal) {
       Iterator<String> iterator = syncal.iterator(); 
       while (iterator.hasNext())
          System.out.println(iterator.next());
       }
   }
}

Output:



Iterating synchronized ArrayList:
Pen
NoteBook
Ink

Method 2: Using CopyOnWriteArrayList

CopyOnWriteArrayList is a thread-safe variant of ArrayList.

package beginnersbook.com;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.Iterator;

public class Details {

 public static void main(String a[]){
    CopyOnWriteArrayList<String> al = new CopyOnWriteArrayList<String>();

    //Adding elements to synchronized ArrayList
    al.add("Pen");
    al.add("NoteBook");
    al.add("Ink");

    System.out.println("Displaying synchronized ArrayList Elements:");
    //Synchronized block is not required in this method
    Iterator<String> iterator = al.iterator(); 
    while (iterator.hasNext())
       System.out.println(iterator.next());
  }
}

Output:

Displaying synchronized ArrayList Elements:
Pen
NoteBook
Ink

How to swap two elements in an ArrayList


This tutorial will help you understand how to swap two elements in an ArrayList. We are using Collections.swap() method for swapping.

public static void swap(List list, int i1, int i2)

This method swaps the element of index i1 with the element of index i2. It throws IndexOutOfBoundsException – if either i1 or i2 is less than zero or greater than the size of the list (i1 < 0 || i1 >= list.size() || i2 < 0 || i2 >= list.size()).

Example of swapping two elements in ArrayList

In this example we have a ArrayList<String> and we are swapping 2nd (index =1) and 5th (index=4) element of ArrayList using Collections.swap() method.



package beginnersbook.com;
import java.util.ArrayList;
import java.util.Collections;

public class SwappingExample {

 public static void main(String a[]){
    ArrayList<String> al = new ArrayList<String>();
    al.add("Sachin");
    al.add("Rahul");
    al.add("Saurav");
    al.add("Sunil");
    al.add("Kapil");
    al.add("Vinod");

    System.out.println("ArrayList before Swap:");
    for(String temp: al){
        System.out.println(temp);
    }

    //Swapping 2nd(index 1) element with the 5th(index 4) element
    Collections.swap(al, 1, 4);

    System.out.println("ArrayList after swap:");
    for(String temp: al){
       System.out.println(temp);
    }
  }
}

Output:

ArrayList before Swap:
Sachin
Rahul
Saurav
Sunil
Kapil
Vinod
ArrayList after swap:
Sachin
Kapil
Saurav
Sunil
Rahul
Vinod

How to override toString method for ArrayList in Java


When we are dealing with ArrayList of Objects then it is must to Override the toString() method in order to get the output in desired format. In this tutorial we will see how to override the toString() method for ArrayList in Java.

Example:

We have two classes here “Student” and “Demo”. Student class has only two properties student name and student age. As you can see that we have overridden the toString() method in Student class itself. In the Demo class we are storing the Student Object in ArrayList and then we iterated the ArrayList using advance for loop. You can very well see that the output is in the format we have specified in toString(). You can give the toString() coding as per your requirement.
package beginnersbook.com;
public class Student 
{
    private String studentname;
    private int studentage;
    Student(String name, int age)
    {
         this.studentname=name;
         this.studentage=age;
    }
    @Override
    public String toString() {
       return "Name is: "+this.studentname+" & Age is: "+this.studentage;
    }
}
Another class:
package beginnersbook.com;
import java.util.ArrayList;
public class Demo
{
     public static void main(String [] args)
     {
          ArrayList<Student> al= new ArrayList<Student>();
          al.add(new Student("Chaitanya", 26));
          al.add(new Student("Ajeet", 25));
          al.add(new Student("Steve", 55));
          al.add(new Student("Mary", 18));
          al.add(new Student("Dawn", 22));
          for (Student tmp: al){
              System.out.println(tmp);
          }
     }
}
Output:


Name is: Chaitanya & Age is: 26
Name is: Ajeet & Age is: 25
Name is: Steve & Age is: 55
Name is: Mary & Age is: 18
Name is: Dawn & Age is: 22
If we wouldn’t have overridden the toString() we would have got the output in below format:
Output of the above programs without overriding toString():
beginnersbook.com.Student@10b28f30
beginnersbook.com.Student@3ad6a0e0
beginnersbook.com.Student@60dbf04d
beginnersbook.com.Student@77d80e9
beginnersbook.com.Student@409a44d6

How to serialize ArrayList in java


ArrayList is serializable by default. This means you need not to implement Serializable interface explicitly in order to serialize an ArrayList. In this tutorial we will learn how to serialize and de-serialize an ArrayList.

Example:

Serialization: Run the below class and it will create a file myfile which will be having ArrayList object in form of Stream of bytes. We would be using “myfile” at the receivers end to recreate the Object from stream of bytes. Note: We did not implemented the Serializable interface in the below class because ArrayList is already been serialized by default.
package beginnersbook.com;
import java.util.ArrayList;
import java.io.*;
public class ArrayListSerialization
{
   public static void main(String [] args)
   {
       ArrayList<String> al=new ArrayList<String>();
       al.add("Hello");
       al.add("Hi");
       al.add("Howdy");

       try{
         FileOutputStream fos= new FileOutputStream("myfile");
         ObjectOutputStream oos= new ObjectOutputStream(fos);
         oos.writeObject(al);
         oos.close();
         fos.close();
       }catch(IOException ioe){
            ioe.printStackTrace();
        }
   }
}
De-Serialization:
In this class we are retrieving the stream of bytes from myfile which we have stored using the above class. We are type casting the returned object to ArrayList and displaying the elements of ArrayList. Observe the output: We are getting the same elements which we have added to the ArrayList before the serialization.


package beginnersbook.com;
import java.io.*;
import java.util.ArrayList;
public class DeSerializationClass 
{
    public static void main(String [] args)
    {
        ArrayList<String> arraylist= new ArrayList<String>();
        try
        {
            FileInputStream fis = new FileInputStream("myfile");
            ObjectInputStream ois = new ObjectInputStream(fis);
            arraylist = (ArrayList) ois.readObject();
            ois.close();
            fis.close();
         }catch(IOException ioe){
             ioe.printStackTrace();
             return;
          }catch(ClassNotFoundException c){
             System.out.println("Class not found");
             c.printStackTrace();
             return;
          }
        for(String tmp: arraylist){
            System.out.println(tmp);
        }
   }
}
Output:
Hello
Hi
Howdy
That’s all I have for the topic serialization of ArrayList. Please let me know if you have any questions.

How to join/combine two ArrayLists in java


In this tutorial we will see how to join (or Combine) two ArrayLists in Java. We will be using addAll() method to add both the ArrayLists in one final ArrayList.

Example:

In this example we are merging two ArrayLists in one single ArrayList and then displaying the elements of final List.
package beginnersbook.com;
import java.util.ArrayList;
public class Details
{
    public static void main(String [] args)
    {
        //First ArrayList
        ArrayList<String> arraylist1=new ArrayList<String>();
        arraylist1.add("AL1: E1");
        arraylist1.add("AL1: E2");
        arraylist1.add("AL1: E3");

        //Second ArrayList
        ArrayList<String> arraylist2=new ArrayList<String>();
        arraylist2.add("AL2: E1");
        arraylist2.add("AL2: E2");
        arraylist2.add("AL2: E3");

        //New ArrayList
        ArrayList<String> al= new ArrayList<String>();
        al.addAll(arraylist1);
        al.addAll(arraylist2);

        //Displaying elements of the joined ArrayList
        for(String temp: al){
            System.out.println(temp);
        }
    }
}
Output:
AL1: E1
AL1: E2
AL1: E3
AL2: E1
AL2: E2
AL2: E3

Comments

Post a Comment

Popular posts from this blog

Java OOPS:OOPS Concepts Overview

Image
  OOPs concepts in Java Object-oriented programming System(OOPs) is a programming paradigm based on the concept of “objects” that contain data and methods. The primary purpose of object-oriented programming is to increase the flexibility and maintainability of programs. Object oriented programming brings together data and its behaviour(methods) in a single location(object) makes it easier to understand how a program works. We will cover each and every feature of OOPs in detail so that you won’t face any difficultly understanding  OOPs Concepts . OOPs Concepts – Table of Contents What is an Object What is a class Constructor in Java Object Oriented Programming Features Abstraction Encapsulation Inheritance Polymorphism Abstract Class and Methods Interfaces in Java What is an Object Object:  is a bundle of data and its behaviour(often known as methods). Objects have two characteristics: They have  states  and  behaviors . Examples of states and behaviors Exam...
Read more

Selenium-Java Contents

  Contents Datatypes In Java String Class In Java  if, if else and nested if else In Java   for loop In Java   while, do while loops In Java   One and two dimensional array In Java   Methods In Java   Access Modifiers In Java   Return Type Of Method In Java   Static, Non Static Methods, Variables In Java   Object In Java   Variable Types In Java   Constructor In Java   Inheritance In Java   Interface In Java   ArrayList In Java   Hashtable In Java   Read-Write Text File In Java   Exception handling, try-catch-finally, throw and throws In Java   Useful Eclipse Shortcuts To Use With Selenium WebDriver Automation Encapsulation In Java Polymorphism In Java What Is An Abstract Class In Java? What Is Method Overloading In Java? Similarities And Difference Between Abstract Class And Interface Usage of "final" Keyword In Java What Is Use Of "Super" Keyword In Java?
Read more

Java OOPS:Constructors in Java – A complete study!!

Image
  Constructors in Java – A complete study!! Constructor is a block of code that initializes the newly created object. A constructor resembles an instance method in java but it’s not a method as it doesn’t have a return type. In short constructor and method are different(More on this at the end of this guide). People often refer constructor as special type of method in Java. Constructor has same name as the class and looks like this in a java code. public class MyClass { //This is the constructor MyClass (){ } .. } Note that the constructor name matches with the class name and it doesn’t have a return type. How does a constructor work To understand the working of constructor, lets take an example. lets say we have a class  MyClass . When we create the object of  MyClass  like this: MyClass obj = new MyClass () The  new keyword  here creates the object of class  MyClass  and invokes the constructor to initialize this newly crea...
Read more