Java – is there a “subclassof” like instanceof?
instanceof can handle that just fine.
java
make[1]: Entering directory error message
make -s suppresses other makefile messages also which might be important for developers. If you want to suppress “Entering/Leaving directory messages” only run make with make –no-print-directory
Java – How Can I Write My ArrayList to a file, and Read (load) that file to the original ArrayList?
You should use Java’s built in serialization mechanism. To use it, you need to do the following: Declare the Club class as implementing Serializable: public class Club implements Serializable { … } This tells the JVM that the class can be serialized to a stream. You don’t have to implement any method, since this is … Read more
Is returning null after exception is caught bad design [closed]
I would say don’t catch the exception if you really can’t handle it. And logging isn’t considered handling an error. Better to bubble it up to someone who can by throwing the exception. If you must return a value, and null is the only sensible thing, there’s nothing wrong with that. Just document it and … Read more
In Java, can I declare a HashMap constant?
Yes, it can be a constant. You should declare your HashMap instance as follows: class <class name> { private static final HashMap<Integer, String> tensNumberConversion = new HashMap<>(); static { tensNumberConversion.put(2, “twenty”); tensNumberConversion.put(3, “thirty”); tensNumberConversion.put(4, “forty”); tensNumberConversion.put(5, “fifty”); tensNumberConversion.put(6, “sixty”); tensNumberConversion.put(7, “seventy”); tensNumberConversion.put(8, “eighty”); tensNumberConversion.put(9, “ninety”); } } However, this is only a constant reference. While … Read more
@MAPSTRUCT. No property named “packaging” exists in source parameter(s)
For those, who have the same issue when using mapstruct + lombok: I had the same issue. The reason was that I’ve been using Lombok plugin too. There’s no need to remove it, but you have to ensure that in pom.xml in <annotationProcessorPaths> Lombok tag is before the Mapstruct one. Example (part of pom.xml file): … Read more
Can volatile variable be defined as static in java?
To expand on Michael’s comment. static simply means not associated with an instance of the containing class. volatile simply means that the value may be changed by other threads without warning. So your question boils down to “can a field not associated with an instance of the containing class be changed by another thread without … Read more
Default access modifier for a Java constructor
Constructors are the same as methods in this respect – if you don’t give an explicit public, private or protected then the constructor gets the default “package private” visibility. It can be called from within the same class or from any other class in the same package, but not from subclasses in a different package … Read more