A thorough understanding of how to choose abstract classes or interfaces, baidu Java post must ask interview questions for four consecutive years

Programmer Xia ya 2021-08-08 21:55:01
thorough understanding choose abstract classes


In fact, I have also summarized the difference between the two , as follows :

abstract class :

(1) The abstract method must be public perhaps protected( Because if it's private, Can't be inherited by subclass , Subclass can't implement this method ), The default is public.

(2) Abstract classes cannot be used to create objects .

(3) If a class inherits from an abstract class , The subclass must implement the abstract method of the parent class . If the subclass does not implement the abstract method of the parent class , The subclass must also be defined as abstract.

(4) The member variables of an abstract class can be of any type .

(5) There can be static code blocks and static methods .

(6) A class can only inherit one abstract class .

(7) Class is “ Is it a relationship ”.

(1) Variables can only be defined as public static final.

(2) Methods can only be abstract , There is no method body .

(3) There can be no static code blocks and static methods .

(4) A class can implement multiple interfaces .

(5) Interface is “ Does it matter ”.

Of course , These differences apply only to Java8 before ,Java8 Your interface can have default methods 、 Static methods , These new features are described below .

Remember the differences I listed , And learn something about Java8 New characteristics , Then there should be no big problem in the interview ~~ however , The interviewer may ask you to give a practical example or give you a scenario to choose , For contestants who can only memorize interview questions , There may be a problem . however , Don't panic. , Let me take you through a very close to life example to let you thoroughly understand how to choose !

How to choose ?


Actually , The above differences have been written , Abstract class is a kind of “ Is it right? ” The relationship between , And the interface is “ Is there any ” The relationship between . therefore , It's easy to think that abstract classes should be a common feature of a class of things , For example, a Person, He has eyes 、 Skin colour , These characteristics that describe a person can be defined in abstract classes , And a person's behavior, such as playing basketball , These can be defined in the interface .

This example is still not obvious , Let me take another example of a real program ape , Speak through actual combat !

For a program . The beginning of the day , You must get up first , Then maintain a variable —— Wake up time , Because everyone gets up at a different time , Is a state quantity , So this wake-up time can't be used final modification , So the interface is pass 了 , Only use abstract classes to maintain this variable .

Then go to work and punch in , You can use a function to describe clocking . Clock in at work. Let's assume that every company requires it hh( Of course, some of the companies I've worked in are flexible , You don't have to punch in and out hh), So this is what every programmer has in common , Should also be placed in abstract class maintenance .

Programming apes certainly can't just write code , You can have some hobbies , Like playing ball , But not every procedural ape likes to play ( Stay at the station and fish hh), Therefore, it is easy to judge that the interface should be selected to maintain the interest of playing .

Come here , Let's write the code :


// Program base class
public abstract class BaseWorker {
// Wake up time
protected int wakeupTime = 7;
// clock in
protected abstract void clockIn();
}

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use protected Modification is mainly to inherit , Let subclasses access .


public interface Interest {
void playBall();
}

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// A procedural ape

public class Worker extends BaseWorker implements Interest {

protected int wakeupTime = 6;
@Override
protected void clockIn() {

//……

}
@Override
public void playBall() {
//……
}

}


however , I want to tell you , The choice of abstract classes and interfaces is not prescriptive , It should be adjusted reasonably according to the business . such as , Basically everyone in our company likes to play , Then, if you still define the playing interest in the interface , We always have to implements This interface , Large amount of code redundancy . therefore , In this case, we can attribute playing to a new worker In an abstract class , Can reduce the implements Amount of writing .
The code is modified as follows :

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// Procedural apes love to play

public class WorkerLikeBall extends BaseWorker{

protected abstract void playBall();

}


such , Just inherit BaseWorker Just get the time to get up and punch in . On the surface, it does not conform to the specification of the abstract class I mentioned earlier , But it's more in line with our demands , Only flexible use can write simple and efficient code .
[](
) Default and static methods for interfaces
-------------------------------------------------------------------------------
After reading what I said above , I believe you have learned how to choose ~ Last , Let's talk about the default and static methods of the interface , These two methods are Java8 New features .
Java8 You can write static methods in the interface , Like the new version of Comparator, Added static Method comparing, Send a function Type interface is enough .

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List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);

int min = list.stream().min(Comparator.comparing(value -> value)).get();

int max = list.stream().max(Comparator.comparing(value -> value)).get();


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版权声明
本文为[Programmer Xia ya]所创,转载请带上原文链接,感谢
https://javamana.com/2021/08/20210808215437475L.html

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