Enthuware

Why option "public abstract boolean test(T t);" is not correct? As I remember, by default all methods in interface are abstract, aren't?

Because this option (option 4) says it is an abstract class. It is not an abstract class, it is an interface.

Answer is (Option 2) and not the (Option 4).
Predicate is a interface and not a Abstract class,Hence it's methods are default Abstract.

Can please someone Confirm and Correct that ??

Not sure what you want to correct. The given answer and the explanation are correct. Please read what option 4 says carefully.

iterator() is listed as both instance method and abstract method of interface Iterable, like this:

Iterator<T> iterator()
Returns an iterator over elements of type T.
Returns:an Iterator

Under Abstract Method and Instance Method.

I thought an interface has 3 type of methods: default method, static method and abstract method; so my question is why is iterator() is a instance method under Iterable API ?

I see there ArrayList has implemented iterator() method;
but I still don't understand instance method iterator() under Iterable interface API.

Please explain.
Thanks.

I've look at it again.
Under interface API, the instance method is a combination of
Default Method and Abstract method.

Hope I had answered my own question correctly.
Thanks.

hasNext() is an abstract method in Iterator interface can be instantiated by Iterable interface which is implemented by ArrayList.

But I don't find hasNext() method in ArrayList.
So, how can a Iterator interface reference call hasNext() ?

like:
Iterator<Employee> i = DataList.iterator();
while(i.hasNext()) {
....
}

Can someone please explain ?
Thanks.

Where you do see ArrayList implementing Iterator interface?? Check out the API here: https://docs.oracle.com/javase/8/docs/a ... yList.html

All Implemented Interfaces:
Serializable, Cloneable, Iterable<E>, Collection<E>, List<E>, RandomAccess

Also, in your code, I don't see you calling hasNext() on an ArrayList object. You are calling it on an Iterator object. This Iterator object, which is returned by calling iterator() method on the ArrayList object, does implement hasNext.

In the answer there is MyCheckEmployee class which has ";" at the end. That shouldn't be there ?

Yes, it is not required but it is not an error either.

Hello, I apologize in advance for my beginners question. It shows my basic understanding is limited, but I am eager to understand it. In the given example a separate interface is created. The explanation reads

it is a very common requirement

. But as the interface doesn't do anything, why can it not be left out? Thus the example code becoming:
This code would do the exact same thing, right? The only reason I can think of now, as to why the interface class is "required", is that it can be seen as handy when other test-classes need to be written (f.e. testing salary above 100,000). And ofcourse the interface CheckEmployee is required in this example to show the connection with Predicate interface. But is it otherwise required as well? With that, what I mean to ask:

Can

This is a very common requirement across applications.

be corrected to

This is a very common use across applications.

(or instead of use, 'implementation')? Or would that be incorrect?

>The only reason I can think of now, as to why the interface class is "required", is that it can be seen as handy when other test-classes need to be written (f.e. testing salary above 100,000).

The requirement refers to the fact that many applications include code that does some kind of filtering/selection of objects available in a collection. For example, while showing a list of items that satisfy a criteria, the application code will need to filter a list of items. So that's the requirement. The requirement is not to have an interface or a class. The requirement is of a feature.

The explanation shows two ways how this requirement can be met - 1. using a customized interface or a customized application specific class. 2. using a standard Predicate interface.

The fun part in software development is to implement something with least amount of new code. You can leave out the Predicate interface and write your own but why would you? and why should a million other developers write a similar class when the job can be done as easily by the Predicate interface (which is already a standard interface available in the Java library)?

admin wrote: ↑

Sun Nov 15, 2015 8:41 am

Because this option (option 4) says it is an abstract class. It is not an abstract class, it is an interface.

Is interface not an abstract class? I think option 2 and option 4 is equal.

No, an interface is an interface. It is not an abstract class.