This question already has answers here:
Java -- private constructor vs final and more
(3 answers)
Closed 7 years ago.
As per my understanding, a class is declared as final to prevent it from being extended/inherited. So I see there can be security and probably some performance gains in this regard.
But is there a very specific design decision behind this? Say for eg: to realize some kind of design pattern? I did go around a similar thread here! but the answer was not really what I was looking for
Singleton Pattern:
-Private Constructor
-Only static methods
-No need to have more than one object of this class or an object at all
-No need to extend this fundamental class
Related
This question already has answers here:
Simple way to understand Encapsulation and Abstraction
(16 answers)
Java Encapsulation Concept not clear
(12 answers)
Closed 4 years ago.
Concept of encapsulation:If we can change the value of private variable indirectly(through setters and getters), then how is the private variable secured, how is it hidden?Could someone please explain in detail..
You're correct. If a field is exposed via getters and setters, it is not encapsulated. It's annoying how many people don't understand this so it's not surprising that you're confused.
Check out this answer. Essentially, using the keyword private we are able to prevent outside use of the fields in a class, for example. It hides the data in a class associated with that private keyword.
This question already has answers here:
What is the difference between public, protected, package-private and private in Java?
(30 answers)
Closed 5 years ago.
I have encountered a weird situation today for second time which keeps my mind busy. The problem has started when i looked Matcher class's constructors which are not declared as private. I thought, i can invoke Matcher's constructor in other class with creating object of it. But my IDE has shown the constructors as private.
Constructors of Matcher class
And i am wondering why cannot i access those constructors? The second time was in Bitmap class from Android Library. I haven't worked with Matcher or any related class. This is the first time, i am dealing with it. I would be grateful if you guys and ladies can help. Thanks in advance. BTW, I am using IntelliJ Idea as IDE.
They are package protected. So you can call those only in classes in the same package.
This question already has answers here:
Difference between static class and singleton pattern?
(41 answers)
Closed 6 years ago.
what is the better approach?
Let us assume a scenario in which there is a utility class that is used by other classes. What is better to use in this case, a singleton class which can be instantiated exactly once or should i make all the fieds static?
In object-oriented programming generally you should avoid singletons and utility classes if possible.
However, if really needed I'd go with utility class without any fields - just static methods. By definition utilities should be rather set of stateless functions. Such are well testable in comparison to untestable singleton (which is done with static field). If you need to keep the state then go towards true objects.
As stated in the comment, you can have a safe singleton done by dependency injection, without static state.
This question already has answers here:
Extend java.lang.String
(6 answers)
Closed 7 years ago.
I want to write a custom method for the String class so that I can call it like the following:
String s = "hello world";
s.myMethod();
Is their a way to accomplish specifically this?
If not then I will just do the following, but I would still like to know.
myMethod(s);
This cannot be done because you can't add methods to existing classes in Java.
It's even more interesting because the class String in Java is a final class, which cannot be subclassed.
You may be interested in this Stack Overflow answer because the thing you are describing is known as monkeypatching, which is common in more dynamic languages than Java. One of the answers links to cglib, one of several libraries that do some magic with the bytecode. Try hard enough and violate basic principles and you can do quite a bit, including making 5 be 3.
Update: This question and its answers seem to address your exact question. Some of the answers are pretty creative.
It is not possible. The best aproach in java would be create your own class that extends from string and write there your method. This way your class would be like string class but including your stuff.
but is not possible because string is final. So create a class that contains just a string object and write ther your method refering to the string. So you can invoke string methods through your string object in your class, and invoke your method through your class directly
This question already has answers here:
Difference between static class and singleton pattern?
(41 answers)
Closed 9 years ago.
Having read Difference between static class and singleton pattern?, none of the answers list any advantages for using a static method over a singleton, which leads me to wonder why anyone would ever want to use static methods.
As with all questions of this nature, use the right tool for the job. Use a singleton when your class represents an object that there can be only one of. Use static methods when your methods are appropriate for the class they are members of but do not rely on a specific instance of that class.
In general, use your best judgment. Go for clean, precise, maintainable code, keeping the overall big picture in mind.