ArrayList in Java

ArrayList in Java, ArrayList is a Class which is use dynamic Arrays to Store Elements.

Things to be Take Note about ArrayList:

• In an ArrayList Class,Element will be shift forward, when an element is being removed from the ArrayList. So the Processing time will be slow
• You can access any Arraylist Elements according to its Array Index Number.
• ArrayList Class is non Synchronized
• ArrayList Class maintain its insertion Order
• Arraylist Class allows duplicate Elements.

In this article. I will create an ArrayList  Example Code and step through , the basic method used  for an ArrayList Class.

class arrayLists

1. First I have created a class called ” arrayLists”
2. And then you will need to import java.util.ArrayList;import java.util.*; both of this Library.
3. Create a new arrayLists object called “animals” .” ArrayList<String> animals = new ArrayList<String>();” 
4. Use the new instance ” animals ” you have just created to add elements into the ArrayList   “animals.add()”.
5. Check the Size of the Array List.  int size = animals.size();
6. Print out the individual Object of the arraylists animals.get(1)
7. Use For Loop to loop through the Element in the Arraylist
8. Use For Each Loop “for (String animal : animals) “ to Loop through the Element in the ArrayList.
9. Use “animals.remove(size – 1); “ to remove the last element ” Hamster ” from the array list.
10. Use the For each Loop to print out the elements inside the Arraylists
11. Use the “Iterator” to print out all elements inside the ArrayLists.

 

import java.util.ArrayList;

import java.util.*;  

public class arrayLists {

	public static void main(String[] args) {
		
		
		// Declaration of a new Array List
		
		ArrayList<String> animals = new ArrayList<String>();
		
		
		// Adding to the List
		animals.add("dog");
		animals.add("Cat");
		animals.add("hamster");
		
		//  Get the Size
		int size = animals.size();
		System.out.println("The size of the list is: " + size);
		
		// Get the Object in the List
		System.out.println("The item on index 1 is: " + animals.get(1));
		
		// Iteration using the ForEach Loop
		
		System.out.println("Iteraton example");
		for (int i = 0; i < size; i++) {
			System.out.println("Item on index " + i + " is: " + animals.get(i));
		}
		
		System.out.println("\nNext for loop example");
		for (String animal : animals) {
			System.out.println("The item is: " + animals);
		}
		
		// Remove the Last Item Hamster
		animals.remove(size - 1);
		
		System.out.println("\nNext for loop example after removing");
		for (String animal : animals) {
			System.out.println("The item is: " + animals);
		}
		
		// Iteration using iterator
		 Iterator  itr= animals.iterator();  
		 while(itr.hasNext()){  
		   System.out.println("Print Out using Iterator");
		   System.out.println(itr.next());  
		  }  
		

	}

}

Add Instance Object into Array List

1. First I have created a class called petstore;
2. Then I create a Constructor for the Class
3. Then i create another Class I called it “accessPet”< to ACCESS the petstore class
4. Create new Instance of “petstores” named Snoopy and Garfields
5. Create new ArrayList for petstores called “cartoonAnimal”
6. Add ” Snoopy and Garfield “ into the newly created Arraylist called ” CartoonAnimal”
7. Iterate Through and Print out all member in the Arraylist

Class petstores

 

package petstore;

public class petstores {
	
	String petname;
	String petType;
	int petAge;
	
	
// Create a Constructor 
	
	public petstores(String petname , String petType ,int petAge){
		
		
		this.petname =petname;
		
		this.petType =petType;
		
		this.petAge =petAge;
		
	}

}

 

Class accessPet

package petstore;
import java.util.*;  

public class accessPet {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		petstores snoopy = new petstores("snoopy","doggy" , 2);
		petstores garfields = new petstores("garfields", "kitty",3);
		
		
		// Create a new ArrayList called  " cartoonAnimal"
		
		 ArrayList<petstores> cartoonAnimal =new ArrayList<petstores>();  
		
		 
		 
		 // Add "snoopy " instance into the Array List " cartoonAnimal"
		 
		// Add "Garfiels " instance into the Array List " cartoonAnimal"
		 cartoonAnimal.add(snoopy);
		 
		 cartoonAnimal.add(garfields);
		 
		  Iterator itr = cartoonAnimal.iterator();  
		  
		  //traversing elements of ArrayList object  
		  
		  while(itr.hasNext()){  
			  petstores ct=(petstores)itr.next();  
		    System.out.println(ct.petname+" "+ct.petType+" "+ct.petAge);  
		  }  
		 
		 
	   

	}

}

 

Check out method of Java arraylist here

Check out Exception Handling in Java here

 

ArrayList in Java Method

No	Method	Description
1	void trimToSize()	trim the size of the ArrayList according to the input Parameter.
2	int indexOf(Object o)	Return index in this list of the first occurrence of the specific element, or return -1 if the List does not contain this element.
3	boolean addAll(int index, Collection c)	Insert elements in the specific collection into this list, starting at the specified position.
4	boolean add(Object o)	Append the specified element to the end of a list.
5	Object[] toArray(Object[] a)	Return array containing elements in this list in the correct sequence.
6	int lastIndexOf(Object o)	Return the index in this list of the last occurrence of theelement, or -1 if the list does not contain this element.
7	void clear()	Remove all of the elements from the list.
8	boolean addAll(Collection c)	append all of the elements in the specific collection to the end of list, to returned by the specified collection’s iterator.
9	void add(int index, Object element)	Insert the specific element at the specified position index in the list.