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Array List: An array has one shortcoming: you have to know how many elements will be in the array when you create it.


 


import java.util.ArrayList;

import java.util.List;

 

public class Welcome {

     

      public static void main(String[] args) {

            ArrayList list1 = new ArrayList();

            ArrayList list2 = new ArrayList(10);

            ArrayList list3 = new ArrayList(list2);

           

            System.out.println("Size list1 " + list1.size() + " Size list2 " + list2.size() + " Size list3 " +list3.size());

           

            ArrayList<String> list4 = new ArrayList<String>();

            ArrayList<String> list5 = new ArrayList<>();

           

            System.out.println("Size list4 " + list4.size() + " Size list5 " + list5.size());

           

            List<String> list6 = new ArrayList<>();

            //ArrayList<String> list7 = new List<>(); // DOES NOT COMPILE

      }

}


 


import java.util.ArrayList;

import java.util.List;

 

public class Welcome {

     

      public static void main(String[] args) {

           

            //List add() method

            ArrayList list1 = new ArrayList();

            list1.add("Hadoop");

            list1.add("Exam");

            list1.add(".com");

            list1.add(0,new Integer(1));

            System.out.println(list1);

           

            //Safe list

            ArrayList<String> list2 = new ArrayList<String>();

            list2.add("Hadoop");

            list2.add("Exam");

            //list2.add(new Integer(1));

            System.out.println(list2);

      }

}


 


import java.util.ArrayList;

import java.util.List;

 

public class Welcome {

     

      public static void main(String[] args) {

           

            //List add() method

            ArrayList list1 = new ArrayList();

            list1.add("Hadoop");

            list1.add("Exam");

            list1.add(".com");

            list1.add(0,new Integer(1));

            System.out.println("Before Element removal "+list1);

           

            list1.remove(0);

            list1.remove(".com");

            System.out.println("After Element removal "+list1);

           

           

      }

}


 


import java.util.ArrayList;

import java.util.List;

 

public class Welcome {

     

      public static void main(String[] args) {

           

            //List add() method

            ArrayList list1 = new ArrayList();

            list1.add("Hadoop");

            list1.add("Exam");

            list1.add(".com");

            list1.add(0,new Integer(1));

            System.out.println("Before Element removal "+list1 + "Size of list = " + list1.size());

           

            list1.remove(0);

            list1.remove(".com");

            System.out.println("After Element removal "+list1 + "Size of list = " + list1.size());

           

            //Check whether list is empty or not.

            System.out.println( list1.isEmpty());

           

            list1.set(0,"www.");

            list1.set(1,"HadoopExam");

            //list1.set(2,".com"); //java.lang.IndexOutOfBoundsException

            System.out.println("After Element Set "+list1 + "Size of list = " + list1.size());

           

            ArrayList list2 = new  ArrayList();

            list2.addAll(list1);

           

            System.out.println(list1.contains("HadoopExam"));

            System.out.println(list1.equals(list2));

            System.out.println(list1 == list2);

      }

}


 


Wrapper Classes


 


-          Each primitive type has a wrapper class.


-          Wrapper class is an Object form of primitive types, with having much more functionalities.


Primitive Types

Wrapper Class

Example

boolean

Boolean

new Boolean(false)

byte

Byte

new Byte( (byte)2)

short

Short

new Short(1 short)

int

Integer

new Integer(1)

long

Long

new Long(1)

float

Float

new Float(1.0)

double

Double

new Double(1.0)

Char

Character

new Character(‘C’)


 


-          We can convert primitive to wrapper and wrapper to primitive class using methods e.g. intValue()


-          String to Wrapper class using valueOf method .


-          String to primitive value using parseInt() method.


 


public class Welcome {

     

      public static void main(String[] args) {

            Integer wInt = new Integer(100);

            System.out.println(wInt.intValue());

            System.out.println(wInt);

           

            System.out.println(Integer.parseInt("1000")); //String to primitive types

            System.out.println(Integer.valueOf("500").getClass()); //String to Wrapper class

            //System.out.println(Integer.valueOf("Hadoop").getClass()); //You will get an RuntimeException here.

      }

}


 


 



 


Autoboxing (Java 1.5 onwards)


-          Java automatically convert the primitive data types to wrapper class, wherever it is required.


import java.util.ArrayList;

import java.util.List;

 

public class Welcome {

  

   public static void main(String[] args) {

         List<Double> doubleList = new ArrayList<Double>();

        

         double val = 26.3;

         System.out.println("Is value added " + doubleList.add(val) + "Content of list" + doubleList);

        

         //Check below how float is converted into double and underline value also changed :(

         float f = 2.1f;

         System.out.println("Is value added " + doubleList.add((double) f) + "Content of list" + doubleList);

         System.out.println("Is value added " + doubleList.add((double) f) + "Content of list" + doubleList);

        

         //Check by removing cast here

         System.out.println("Is value removed " + doubleList.remove((double) f) + "Content of list" + doubleList);

        

         //Now add null value in list

         System.out.println("Is value added " + doubleList.add(null) + "Content of list" + doubleList);

         System.out.println("Is value added " + doubleList.add(null) + "Content of list" + doubleList);

        

         //Now add null value in list

         System.out.println("Is value removed " + doubleList.remove(null) + "Content of list" + doubleList);

        

        

   }

}                         


 


 


-          Autoboxing and methods in an Integer ArrayLists (Check Index position or actual value is being removed ?)


import java.util.ArrayList;

import java.util.List;

 

public class Welcome {

  

   public static void main(String[] args) {

        

         List<Integer> list = new ArrayList<Integer>();

        

         list.add(1);

         list.add(2);

        

         System.out.println("Contents in the list = " + list);

        

         //Check the surprise by un-commenting below methods

         //list.remove(1);

         list.remove(new Integer(1));

         System.out.println("Contents in the list = " + list);

        

        

   }

}                         


 


Convert Array and List


-          When you convert array to list, lists are backed by arrays. Hence, whatever operation you will apply on arrays will also be reflected In lists.


-          You can also convert List to arrays back.


import java.util.ArrayList;

import java.util.Arrays;

import java.util.Collections;

import java.util.List;

 

public class Welcome {

  

   public static void main(String[] args) {

        

         String[] s1 = new String[5];

         s1[0] = "Hadoop";

         s1[1] = "Exam";

         s1[2] = ".com";

        

         System.out.println(s1.length);

        

         List<String> sList = new ArrayList<String>();

         sList = Arrays.asList(s1);

         System.out.println(sList);

        

         s1[0] = "Training4"; // Chenage 1st element in array

         System.out.println(sList);

        

         System.out.println(sList.toArray());

         //Below changes will be applied to both array and lists

         sList.set(0, "www.");

         sList.set(1, "HadoopExam");

         sList.set(3, "Learning");

         sList.set(4, "Resources");

         System.out.println(sList);

         //Sorting the list

         Collections.sort(sList);

         System.out.println(sList);

        

   }

}                                                                                                    


 

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