Swapna latha

Tim Holloway wrote:An Interface is a contract. If a class implements an Interface, then it has promised that it will have implemented all of the methods defined in the Interface.

That's useful for a number of reason, including plug-replaceable components. And in particular test components.

If you have an interface definition you can construct a dummy or mock class that implements the indicated methods but does not have to actually do all the work that the "real" class does. That means that you can test your team's code without having to wait for the other team to deliver the "real" class.

Note that I distinguish between a "dummy" class and a "mock" class. In this context, a dummy class is simply a class that you implement yourself to test with. A Mock class is usually controlled by a mocking framework. Given a choice, I prefer dummy classes, but a mocked class can often be used in an environment where you need to pretend to connect to complex infrastructure and a dummy class can't be used.

Agreed. Let me frame and example on that. Correct me if i am going wrong

Ex:
public class House{};
public class RedHouse extends House{}
public class BlueHouse extends House{}

public interface Student{

House getHouse(List<House> houses, String studentLastName);

}

dummy class :

public class StudentImpl imlements Student{

List<Houses> houses = new ArrayList<>();
houses.add("RedHouse");
houses.add("BlueHouse");

@Override
House getHouse(houses, "lastName"){
return houses.get(0);
}

}

My team can use this  dummy class for testing and can write about House, RedHouse, BlueHouse etc.,

The other team can write the exact logic for getHouse with students last name and the houses list for a school. The other team will write the implementation of StudentImpl with business rules

Thus both teams can be engaged with interface as centric.

Hi Team,

I was just going through the Java 1.8 OCP book by Jeanne and Scott and there they mentioned about mock interface so that two different teams can do programming and join their code later.

I am not clear about the example quoted in the book , could any one please help me with few different and easily understandable examples.

Best Regards,

Swapna Kori

Hi All,

I am really confused in applying lambda map function where as the code which i am reading has got the result.

//Written by me MapFunction<String,Tuple2<Integer,String>> mapFunction = s-> { String[] words = s.split(","); return new Tuple2<Integer,String>(Integer.parseInt(words[0]),words[1]); }; DataSet<Tuple2<Integer,String>> personSet = env.readTextFile("C:\\Users\\513848\\person").map(mapFunction); //Code i found in google which is working like a charm DataSet<Tuple2<Integer, String>> personSet1 = env.readTextFile("C:\\Users\\513848\\person").map(new MapFunction<String, Tuple2<Integer, String>>()                                     { public Tuple2<Integer, String> map(String value) { String[] words = value.split(",");                                                 // words = [ {1} {John}] return new Tuple2<Integer, String>(Integer.parseInt(words[0]), words[1]); } });

What i am doing wrong ? Please guide me .

Thanks & Regards,

Swapna.

Hi, I am working on few examples on Threads and i do see that Thread class has an Functional interface inside it.

I have seen an example in an udemy course like:

public class Main2 {    public static void main(String [] args) {        Thread thread = new Thread(new Runnable() {            @Override            public void run() {                //Code that will run in a new thread                throw new RuntimeException("Intentional Exception");            }        });        thread.setName("Misbehaving thread");        thread.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {            @Override            public void uncaughtException(Thread t, Throwable e) {                System.out.println("A critical error happened in thread " + t.getName()                        + " the error is " + e.getMessage());            }        });        thread.start();    } }

Could any one please exaplain the advantage of functional interface in a class.

Thank you very much Sharma.

Ng Sharma wrote:Best Answer.

https://stackoverflow.com/questions/4343202/difference-between-super-t-and-extends-t-in-java

Stephan van Hulst wrote:On a tangent: In general you don't need to worry about the A parameter. You only need to care about it if you implement your own Collector.

Thank you Stephan.

Thank you very much Tim. I got the answer now.

Tim Holloway wrote:Try this with 1:59 instead of 2:00. You might find it interesting. Indeed, try 1:59:59

Campbell Ritchie wrote:But Comparator is a functional interface.

Got it Campbell. Thank you very much.

But I have used BiFunction above. Comparator is not a Bifunction right.

Campbell Ritchie wrote:But Comparator is a functional interface.

Campbell Ritchie wrote:Have you seen the documentation for Collections#sort()?

Yes Campbell, it takes the second argument as Comparator but not function. So confused at this part.

Thanks & Regards,

Swapna

Stephan van Hulst wrote:You need to tell us what part of the explanation is not clear to you, and explain to us why you think it is 0.

Stephan, the lines of codes are as follows with my explanation . Correct me if i am wrong

LocalDateTime ld1 = LocalDateTime.of(2015, Month.NOVEMBER, 1, 2, 0); // This line of code is having a time of 2 AM so as per DST savings, it should become 1 AM
ZonedDateTime zd1 = ZonedDateTime.of(ld1, ZoneId.of("US/Eastern"));
LocalDateTime ld2 = LocalDateTime.of(2015, Month.NOVEMBER, 1, 1, 0);// There wont be any change of time as the time is still 1 AM and time changes after 2 AM
ZonedDateTime zd2 = ZonedDateTime.of(ld2, ZoneId.of("US/Eastern"));// As both the times are 1 AM , the result is zero.

Thanks & Regards,

Swapna.

Hi All,

I am practising questions from both enthuware and whizlab and i have got struck in understanding how does sort method takes function as 2nd argument.

public class Whizlab{           public static void main(String[] args){                              List<String> strings = new ArrayList<>();                   strings.add("Shane");                   strings.add("Rachel");                   strings.add("Raj");                       BiFunction<String, String, Integer> func = (s1,s2) -> Integer.compare(s1.length(), s2.length());                                     Collections.sort(strings, func::apply);// Question is how function as 2nd argument to sort method.                                     System.out.println(strings);       }   }

Question is how function as 2nd argument to sort method.

Thanks & Regards,

Swapna.

Stephan van Hulst wrote:What part don't you understand?

Stephan, I am not sure how the answer is -2. I still think answer is 0. The explanation given by enthuware is not clear to me.


Thanks & Regards,

Swapna.

I am practising enthuware questions and i got confused in one of the question and is as follows:

Given that daylight Savings Time ends on Nov 1 at 2 AM in US/Eastern time zone. (As a result, 2 AM becomes 1 AM.), what will the following code print? LocalDateTime ld1 = LocalDateTime.of(2015, Month.NOVEMBER, 1, 2, 0); ZonedDateTime zd1 = ZonedDateTime.of(ld1, ZoneId.of("US/Eastern")); LocalDateTime ld2 = LocalDateTime.of(2015, Month.NOVEMBER, 1, 1, 0); ZonedDateTime zd2 = ZonedDateTime.of(ld2, ZoneId.of("US/Eastern")); long x = ChronoUnit.HOURS.between(zd1, zd2); System.out.println(x);

The options are :
1
-1
0
2
-2
This will not compile.

When i have chosen it as 0 , but i see that that answer from enthuware is -2.

Explanation by enthuware software guys is as follows:

Think of it as follows -
The time difference between two dates is simply the amount of time you need to go from date 1 to date 2.
So if you want to go from 1AM to 2AM, how many hours do you need? On a regular day, you need 1 hour. That is, if you add 1 hour to 1AM, you will get 2AM. However, as given in the problem statement, at the time of DST change, 2 AM becomes 1AM. That means, even after adding 1 hour to 1AM, you are not at 2AM. You have to add another hour to get to 2 AM. In total, therefore, you have to add 2 hours to 1AM to get to 2AM.

The answer can therefore be short listed to 2 or -2. Now, as per the JavaDoc description of the between method, it returns negative value if the end is before the start. In the given code, our end date is 1AM, while the start date is 2AM. This means, the answer is -2.

I am not clear about the explanation of Enthuware guys

Thanks

Swapna

Hi All,

I am practising OCP questions by Enthuware and the code is as follows:

public class ImmutableDoubleExample {    public static void main(String[] args) {        List<Double> dList = Arrays.asList(10.0,20.0);        dList.stream().forEach(x->{x=x+10;});        dList.stream().forEach((d-> System.out.println("d = " + d)));    } }

Can we reuse the stream as i used stream once with dList and also the second time.

Thanks & Regards,

Swapna