The title pretty much sums it up. I'm wondering if I need to include static variables (which I probably don't) in the constructor.
Given that static variables are static I suspect that they are probably not. But I didnt find any answers to this question on stackoverflow.
No static fields are skipped while using these lombok annotations
#NoArgsConstructor
#RequiredArgsConstructor
#AllArgsConstructor
Static fields are skipped by these annotations.
If you want to declare constructor with static fields then you can declare the one explicitly, but you might end up with compiler error if any of those constructors have same signature
Unlike most other lombok annotations, the existence of an explicit constructor does not stop these annotations from generating their own constructor. This means you can write your own specialized constructor, and let lombok generate the boilerplate ones as well. If a conflict arises (one of your constructors ends up with the same signature as one that lombok generates), a compiler error will occur.
The answer is no as you can check in javadoc:
An all-args constructor requires one argument for every field in the class.
or official documentation: https://projectlombok.org/features/Constructor
RequiredArgsConstructor includes in the constructor all final fields. However, you cannot have a static final variable not initialized (as they can be used even with no instance of that class)
Related
Lombok offers a variety of annotations for java constructors, including but not limited to #AllArgsConstructor and #RequiredArgsConstructor. What is the difference between these two and when do you use one over the other? I found this documentation but the verbiage is a little convoluted and I'm having trouble following the basic differences between the two.
In short, use #AllArgsConstructor to generate a constructor for all of your class's fields and use #RequiredArgsConstructor to generate a constructor for all class's fields that are marked as final.
From the documentation,
#AllArgsConstructor generates a constructor with 1 parameter for each field in your class.
#RequiredArgsConstructor generates a constructor with 1 parameter for each field that requires special handling. All non-initialized final fields get a parameter, as well as any fields that are marked as #NonNull that aren't initialized where they are declared.
I know what it means in a comment for documentation purposes, but outside of that what does it mean? (I would normally just google this but every non letter symbol shows up in results)
The # symbol denotes a Java Annotation. What a Java annotation does, is that it adds a special attribute to the variable, method, class, interface, or other language elements. (This can be configured when you declare the annotation) When you add an annotation to something, other parts of the program can check whether something has an annotation or not. It then can use this information to do whatever stuff they need.
Let me give you some examples:
The #Override annotation
public class SuperClass {
public void someInterestingMethod() {
System.out.println("Superclass!");
}
}
public class DerivedClass extends SuperClass {
public void someInterestngMethod() {
System.out.println("Derived class!");
}
}
And when you do this:
SuperClass sc = new DerivedClass();
sc.someInterestingMethod();
The someInterestingMethod() call should be dynamically dispatched, and print "Derived class!", right? Well the derived class' method was actually misspelled, so DerivedClass got its own separate method called someInterestngMethod(), totally unrelated to the superclass' someInterestingMethod(). As such, someInterestingMethod() is no longer overridden, and the superclass' implementation is invoked.
The #Override keyword is intended to help with this. It signals your intent to the compiler, that you would like the annotated method to be an overload of one of the ancestor class' methods. If it's not (such as in this typo case, or if the SuperClass API changed and renamed the method), the will fail your compilation, to alert your attention to the broken override.
The #SuppressWarnings Annotation
Here is a method:
public void someMethod() {
int i;
}
There will be a compiler warning saying that i is never used. So you can add the #SuppressWarnings to the method to suppress the warning:
#SuppressWarnings("unused")
public void someMethod() {
int i;
}
Note that there is a parameter to the #SuppressWarnings annotation. Some annotations have parameters and you can look for the them in the javadoc. But for those that don't have parameters you don't need to add () like a method.
You can also declare your own annotations and use reflection to check for them. The above 2 annotations will be checked by the compiler.
The # sign is used to specify Java Annotation.
https://en.wikipedia.org/wiki/Java_annotation
There are built-in Java Annotation and user defined Custom Annotation.
Annotations are used in various ways, such as suppress warning, associate method to URI (Servlet), associate variables to resource (JNDI) etc
The # symbol is used for annotations. In my experience, the most common annotation is #Override, which indicates that a method is declared in a superclass. Other common annotations are #Deprecated, indicating that a method should no longer be used but still exists for backwards compatibility, and #SupressWarnings, to prevent warnings from showing up in the compiler.
Note that it's actually possible to get annotations which are not included in the core Java libraries and to declare your own annotations.
The # symbol denotes Annotations. They provide information about a class, its field or method (above which they appear). They cannot perform operations. The compilers or special annotation processors use this information to make writing code less verbose.
In Java Persistence API you use them to map a Java class with database tables.
For example
#Table()
Used to map the particular Java class to the date base table.
#Entity
Represents that the class is an entity class.
Similarly you can use many annotations to map individual columns, generate ids, generate version, relationships etc.
As some other suggests, it is Java's annotation. It helps the compiler to validate your code and to notify the programmer as well.
Very simple code example:
public class SomeClass {
#Override
public String toString() {
return "SomeClass";
}
#Deprecated
public void doSomeOperation() {
// some operation...
}
}
The annotation from SomeClass#toString which is #Override helps the compiler to determine that it is an overridden function from the implicit inheritance to the class Object.
While the annotation from SomeClass#doSomeOperation will warn the programmer that the function itself is deprecated already and should be avoided to use.
The annotations are for the reader or compiler, not executable code.
According to the documentation of SafeVarargs, the #SafeVarargs annotation can be applied only to constructors or variable arity methods that are either static or final. This is, I have read, to eliminate issues with annotation inheritance; that is to say, annotations on methods are only allowed if the method cannot be overridden. Clearly, constructors, static methods, and final methods cannot be overridden. However, neither can private methods or methods in a final class. Someone has complained about the inability to designate #SafeVarargs private methods, but neither of these issues has been addressed. In general, no one really seems to care. Am I missing something? Am I complaining about something that doesn't have any practical applications? Or... ?
This is scheduled to be fixed in Java 9; see http://openjdk.java.net/jeps/213 .
It is common in Java classes to have lots of getter and setter methods, one each for every data model class variable. I realize that many IDEs will create these for you, but I'm trying to avoid this clutter and not have all these methods in my classes. So, is there any way to access a variable in a read only fashion outside the class (as if it were public final), while retaining write access inside the class or subclass exclusively (as if it were private or protected).
The only pseudo-solution I've come up with is a base class (or interface with default methods) that has a get(String variableName) method which then gets the fields of the class via reflection and returns the appropriate one. The downside is that for that to work, the variables have to be public, so only by convention does it meet my requirements (in that in the extending/implementing class that has the variables I want to access, I only call the get method from outside the class, and don't implement a set method). The main thing I don't like about this is that if a variable name changes, callers of the get methods will not cause compiler errors, since the variable name is just a hardcoded String.
Anyone have a better idea?
Yes - try to design your classes so you don't have getters and setters at all. Typically it's a bad design to have getters and setters on all of your fields because it breaks encapsulation. An exception is the case of Java Beans (where you have a model class/DTO or some class that's mapped to XML/JSON); here you should not mind them because setters and getters are the only methods.
In classes that have logic, inject your dependencies via constructor or directly if you use Spring/CDI and you like it. This is more safe because you won't have objects in inconsistent states; like for example you create an object but forget to call a setter -> NullPointerException. But by using constructors, you avoid the case of forgetting to call the setters.
Of course there might be exceptions, like when setting some optional fields when you don't want all the dependencies in the constructor all the time. This however can be solved with overloading constructors or if the case is more complex the problem can be solved in a more elegant way by using the builder pattern.
See a great article on this: http://www.javaworld.com/article/2073723/core-java/why-getter-and-setter-methods-are-evil.html
You may use lombok - to manually avoid getter and setter method. But it create by itself.
The using of lombok significantly reduces a lot number of code. I found it pretty fine and easy to use. But here you may find some pros and cons of using lombok here.
Hope it will help.
Thanks a lot.
Java FX introduced something similar to what you want: ReadOnlyProperty
Might not be exactly what you are looking for, though. In general, I don't think exposing a variable is a good idea.
According to the documentation of SafeVarargs, the #SafeVarargs annotation can be applied only to constructors or variable arity methods that are either static or final. This is, I have read, to eliminate issues with annotation inheritance; that is to say, annotations on methods are only allowed if the method cannot be overridden. Clearly, constructors, static methods, and final methods cannot be overridden. However, neither can private methods or methods in a final class. Someone has complained about the inability to designate #SafeVarargs private methods, but neither of these issues has been addressed. In general, no one really seems to care. Am I missing something? Am I complaining about something that doesn't have any practical applications? Or... ?
This is scheduled to be fixed in Java 9; see http://openjdk.java.net/jeps/213 .