Some important points of Abstract class

Some important points of Abstract class-

- We can't create the object of abstract class but abstract class have constructor.
- Abstract class constructor is called via super() call from child class constructor.
- Abstract class does not allow abstract method static. if you does it's abstract method static then compiler gives you compilation error message - 
     illegal combination of modifiers: 'abstract' and 'static' .
- We can apply static with non-abstract method inside Abstract class.

public class AbstarctionDemo extends  MarketChoice{

public AbstarctionDemo(String[] productName) {

super(productName);

// TODO Auto-generated constructor stub

}

public static void main(String[] args) {

// TODO Auto-generated method stub

        String[] productName= {"mouse","keyboard","desktop","cpu","speaker"};

MarketChoice marketChoice= new AbstarctionDemo(productName);

marketChoice.getDetails();

}

@Override

public void getMarketDetails() {

// TODO Auto-generated method stub

//marketChoice

}

}

abstract class MarketChoice {

protected String[] pName;

//Abstract class constructor  

public MarketChoice(String[] name){

pName=name;

}

public abstract void getMarketDetails();

 void getDetails(){

for (String string: pName) {

System.out.println(string);

} 

}

}

Important features of java 8

Some important features of java 8 are listed below-

• forEach() method in Iterable interface
• default and static methods in Interfaces
• Lambda Expressions
• Java Time API
• Java Stream API for Bulk Data Operations on Collections

1. forEach using Map and List interface

EXAMPLE-

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

public class Java8Feature {

public static void main(String[] args) {

// TODO Auto-generated method stub

Java8Feature obj = new Java8Feature();

System.out.println("*** forEach with Map ***");

obj.myMapIterator();

System.out.println("*** forEach with List ***");

obj.myListIterator();

}

void myMapIterator() {

Map<String, Integer> items = new HashMap<>();

items.put("A", 10);

items.put("B", 20);

items.put("C", 30);

items.put("D", 40);

items.put("E", 50);

items.put("F", 60);

//1. Filter map using normal way

for (Map.Entry<String, Integer> entry : items.entrySet()) {

System.out.println("Item : " + entry.getKey() +" Count : "+ entry.getValue());

}

//2. Filter map using Lambda expression

items.forEach((k, v) -> System.out.println("Item : " +k +" Count : " + v));

//3. Filter map using Lambda expression

items.forEach((k, v) -> {

System.out.println("Item : " + k +" Count : " + v);

if ("E".equals(k)) {

System.out.println("Hello E");

}

});

}

void myListIterator() {

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

items.add("A");

items.add("B");

items.add("C");

items.add("D");

//1. Filter list using normal way

for (String string : items) {

System.out.println("Item : " + string);

}

//2. Filter list using Lambda expression

items.forEach(sanjay -> System.out.println(sanjay));

//3. Filter list using Lambda expression

items.forEach(aaa -> {

if ("C".equals(aaa)) {

System.out.println("Lambda expression");

}

});

//4. Filter using method reference 

items.forEach(System.out::print);   

              // Work like below 

              //items.forEach(i-> System.out.println(i));

//5. Stream and filter

items.stream()

.filter(s->s.contains("B"))

.forEach(System.out::println);

}
}

2. default and static methods in Interfaces

default method of java 8 gives a flexibility to modify or add new upcoming feature in future on existing interface. default method does not effect to all other implementer classes if something is changed on default method, because default method is optional for exiting implementer classes to use default method even not need to override it by all implementer classes.

default method does not create ambiguity if 2 interface having same default method name. its is accessed via interface name.

EXAMPLE-

public class Java8InterfaceDefaultMethod implements IConsumerUpdate ,IMarketProduct ,IMarketInventry{

public static void main(String[] args) {

// TODO Auto-generated method stub

Java8InterfaceDefaultMethod obj = new                                                                    Java8InterfaceDefaultMethod();

int saleCount = obj.getProductSaleCount(10);

System.out.println("Product sale count : " + saleCount);

String pName = obj.getProductName();

System.out.println("Product Name : " + pName);

obj.getConsumer();

String pQuality=IMarketProduct.getProductQuality();

System.out.println("product quality : " +pQuality);

}

@Override

public int getProductSaleCount(int saleCount) {

// TODO Auto-generated method stub

return saleCount;

}

@Override

public int getInventryCount() {

// TODO Auto-generated method stub

return 0;

} 

}

interface IMarketProduct {

String productName = "MacBook pro";

String productQuality = "Normal";

int getProductSaleCount(int count);

default String getProduct() {

return productName;

}

static String getProductQuality() {

return productQuality;

}

}

interface IMarketInventry {

String name = "Windows laptop";

int getInventryCount();

default String getProductName() {

return name;

}

}

interface IConsumerUpdate {

default void getConsumer() {

System.out.println("I am Consumer");

}

}

3. Lambda Expressions

public class ThreadEvenOdd {

    int inputNum=13;

public ThreadEvenOdd(int a) {

super();

this.inputNum = a;

}

public static boolean checkPrime(int n) {

for (int i = 2; i < n; i++) {

if (n % i == 0)

return false;

}

return true;

}

public static void main(String[] args) {

// TODO Auto-generated method stub

int inputNumber=13;

ThreadEvenOdd obj = new ThreadEvenOdd(inputNumber);

/**

* Using Lambda expression introduced in java 8

*/

Runnable runnable = () -> {

// TODO Auto-generated method stub

for (int i = 0; i < obj.inputNum; i++) {

try {

if (i % 2 == 0) {

   System.out.println("Even nuber is: " + i);

}

Thread.sleep(0);

} catch (InterruptedException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

};

/**

* using java 7

*/

Runnable runnable2 = new Runnable() {

@Override

public void run() {

// TODO Auto-generated method stub

for (int i = 0; i < obj.inputNum; i++) {

try {

if (i % 2 != 0) {

System.out.println("odd nuber is: " + i);

}

Thread.sleep(0);

} catch (Exception e) {

e.getMessage();

}

}

}

};

/**

*  Using Lambda expression introduced in java 8

*/

Runnable runnable3 = () -> {

// TODO Auto-generated method stub

for (int i = 2; i < obj.inputNum; i++) {

if (checkPrime(i)) {

System.out.println("Prime number " + i);

}

}

};

Thread t = new Thread(runnable);

Thread t1 = new Thread(runnable2);

Thread t2 = new Thread(runnable3);

t.start();

t1.start();

t2.start();

}

}