Module-8B

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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.

- 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);

//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);

//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);

}