[Java - ArrayList Basic]#Java #ArrayList #tutorial #interview

2 - How to initialize an ArrayList.md

Method 1: Initialization using Arrays.asList

Syntax:

ArrayList<Type> obj = new ArrayList<Type>(Arrays.asList(Object o1, Object o2, Object o3, ....so on));

Example:

import java.util.*;
public class InitializationExample1 {
   public static void main(String args[]) {
	   ArrayList<String> obj = new ArrayList<String>(
		Arrays.asList("Pratap", "Peter", "Harsh"));
	  System.out.println("Elements are:"+obj);
   }
}

Output:

Elements are:[Pratap, Peter, Harsh]

Method 2: Anonymous inner class method to initialize ArrayList

Syntax:

ArrayList<T> obj = new ArrayList<T>(){{
		   add(Object o1);
		   add(Object o2);
		   add(Object o3);
                   ...
                   ...
		   }};

Example:

import java.util.*;
public class InitializationExample2 {
   public static void main(String args[]) {
	   ArrayList<String> cities = new ArrayList<String>(){{
		   add("Delhi");
		   add("Agra");
		   add("Chennai");
		   }};
	  System.out.println("Content of Array list cities:"+cities);
   }
}

Output:

Content of Array list cities:[Delhi, Agra, Chennai]

Method3: Normal way of ArrayList initialization

Syntax:

ArrayList<T> obj = new ArrayList<T>();
	   obj.add("Object o1");
	   obj.add("Object o2");
	   obj.add("Object o3");
                        ...
                        ...

Example:

import java.util.*;

public class Details {
   public static void main(String args[]) {
	   ArrayList<String> books = new ArrayList<String>();
	   books.add("Java Book1");
	   books.add("Java Book2");
	   books.add("Java Book3");
	  System.out.println("Books stored in array list are: "+books);
   }
}

Output:

Books stored in array list are: [Java Book1, Java Book2, Java Book3]

Method 4: Use Collections.ncopies

Collections.ncopies method can be used when we need to initialize the ArrayList with the same value for all of its elements.

Syntax:

count is number of elements and element is the item value

ArrayList<T> obj = new ArrayList<T>(Collections.nCopies(count, element));

Example:

import java.util.*;

public class Details {
   public static void main(String args[]) {
	   ArrayList<Integer> intlist = new ArrayList<Integer>(Collections.nCopies(10, 5));
	  System.out.println("ArrayList items: "+intlist);
   }
}

Output:

ArrayList items: [5, 5, 5, 5, 5, 5, 5, 5, 5, 5]

3 - How to loop ArrayList in Java.md

There are four ways to loop ArrayList:

1. For Loop
2. Advanced for loop
3. While Loop
4. Iterator

import java.util.*;
public class LoopExample {
   public static void main(String[] args) {

      ArrayList<Integer> arrlist = new ArrayList<Integer>();
      arrlist.add(14);
      arrlist.add(7);
      arrlist.add(39);
      arrlist.add(40);

      /* For Loop for iterating ArrayList */
      System.out.println("For Loop");
      for (int counter = 0; counter < arrlist.size(); counter++) { 		      
          System.out.println(arrlist.get(counter)); 		
      }   		

      /* Advanced For Loop*/ 		
      System.out.println("Advanced For Loop"); 		
      for (Integer num : arrlist) { 		      
           System.out.println(num); 		
      }

      /* While Loop for iterating ArrayList*/ 		
      System.out.println("While Loop"); 		
      int count = 0; 		
      while (arrlist.size() > count) {
	 System.out.println(arrlist.get(count));
         count++;
      }

      /*Looping Array List using Iterator*/
      System.out.println("Iterator");
      Iterator iter = arrlist.iterator();
      while (iter.hasNext()) {
         System.out.println(iter.next());
      }
   }
}

Output:

For Loop
14
7
39
40
Advanced For Loop
14
7
39
40
While Loop
14
7
39
40
Iterator
14
7
39
40

5. How to iterate arraylist elements using Enumeration interface

import java.util.Enumeration;
import java.util.ArrayList;
import java.util.Collections;
 
public class EnumExample {
 
   public static void main(String[] args) {
      //create an ArrayList object
      ArrayList<String> arrayList = new ArrayList<String>();
 
      //Add elements to ArrayList
      arrayList.add("C");
      arrayList.add("C++");
      arrayList.add("Java");
      arrayList.add("DotNet");
      arrayList.add("Perl");
 
      // Get the Enumeration object
      Enumeration<String> e = Collections.enumeration(arrayList);
 
      // Enumerate through the ArrayList elements
      System.out.println("ArrayList elements: ");
      
      while(e.hasMoreElements()) {
      	System.out.println(e.nextElement());
      }
   }
}

Output:

ArrayList elements: 
C
C++
Java
DotNet
Perl

4 - How to find length of ArrayList in Java.md

By using size() method of ArrayList class we can easily determine the size of the ArrayList.

public int size()

Example:

package beginnersbook.com;
import java.util.ArrayList;
public class Details
{
    public static void main(String [] args)
    {
        ArrayList<Integer> al=new ArrayList<Integer>();
        
        System.out.println("Initial size: "+al.size());
        
        al.add(1);
        al.add(13);
        al.add(45);
        al.add(44);
        al.add(99);
        
        System.out.println("Size after few additions: "+al.size());
        
        al.remove(1);
        al.remove(2);
        
        System.out.println("Size after remove operations: "+al.size());
        
        System.out.println("Final ArrayList: ");
        
        for(int num: al){
            System.out.println(num);
        }
   }
}

Output:

Initial size: 0
Size after few additions: 5
Size after remove operations: 3
Final ArrayList: 
1
45
99