Take a look here: Understanding Instance and Class Members When a number of objects are created from the same class blueprint, they each have their own distinct copies of instance variables. (…) Sometimes, you want to have variables that are common to all objects. This is accomplished with the static modifier. Fields that have the static modifier … Read more
From a blog post: To use javac from JDK N to cross-compiler to an older platform version, the correct practice is to: Use the older -source setting. Set the bootclasspath to compile against the rt.jar (or equivalent) for the older platform. If the second step is not taken, javac will dutifully use the old language rules … Read more
For a completely stateless utility class in Java, I suggest the class be declared public and final, and have a private constructor to prevent instantiation. The final keyword prevents sub-classing and can improve efficiency at runtime. The class should contain all static methods and should not be declared abstract (as that would imply the class is not concrete and has to be implemented in … Read more
The clearest way to express polymorphism is via an abstract base class (or interface) This class is abstract because the goPee() method is not definable for Humans. It is only definable for the subclasses Male and Female. Also, Human is an abstract concept — You cannot create a human that is neither Male nor Female. It’s got … Read more
There is a compile error that occurred earlier during the build. Look for that error in the same output log file and try to fix it.
ArrayList is unique in its naming standards. Here are the equivalencies: Note that unshift does not remove an element, but instead adds one to the list. Also note that corner-case behaviors are likely to be different between Java and JS, since they each have their own standards.
In short: OpenJDK has multiple meanings and can refer to: free and open source implementation of the Java Platform, Standard Edition (Java SE) open source repository — the Java source code aka OpenJDK project prebuilt OpenJDK binaries maintained by Oracle prebuilt OpenJDK binaries maintained by the OpenJDK community AdoptOpenJDK — prebuilt OpenJDK binaries maintained by community (open source … Read more
JAVA_OPTS is the standard environment variable that some servers and other java apps append to the call that executes the java command. For example in tomcat if you define JAVA_OPTS=’-Xmx1024m’, the startup script will execute java org.apache.tomcat.Servert -Xmx1024m If you are running in Linux/OSX, you can set the JAVA_OPTS, right before you call the startup script by doing This will … Read more
Have you tried using new File(“logo.jpg”); (without the leading /)? And are you sure, the logo.jpg is copied to your output? (Some IDEs don’t copy every file from your source-directories to your output (or target) directories.) becomes (Note that the IDE/compiler does not copy the image to your output-directory and so the compiled code cannot … Read more
This is a typical bidirectional consistency problem. It is well discussed in this link as well as this link. As per the articles in the previous 2 links you need to fix your setters in both sides of the bidirectional relationship. An example setter for the One side is in this link. An example setter … Read more