First, To compile the java source file using javac you need to specify the files to compile explicitly. Example: you need not provide the path if the source file is in the current working directory. Second, whenever java encounters import abc.xyz.ClassName; it tries to resolve abc/xyz/ClassName with respect to the classpath or current working directory. … Read more
On invoking overridable method from constructors Simply put, this is wrong because it unnecessarily opens up possibilities to MANY bugs. When the @Override is invoked, the state of the object may be inconsistent and/or incomplete. A quote from Effective Java 2nd Edition, Item 17: Design and document for inheritance, or else prohibit it: There are … Read more
From the javadoc: The serialization runtime associates with each serializable class a version number, called a serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization. If the receiver has loaded a class for the … Read more
OK what I am trying to do here is create a game where the object/ball is controlled by clicking on the object with the mouse, pulling back the mouse (the distance the mouse is pulled back will determine the velocity of the object) and on releasing the button the object will move (it’s angle of … Read more
Problem This ArrayIndexOutOfBoundsException: 0 means that the index 0 is not a valid index for your array args[], which in turn means that your array is empty. In this particular case of a main() method, it means that no argument was passed on to your program on the command line. Possible solutions If you’re running … Read more
The problem is here: The left-hand-side is a value. Not a variable. That’s why you can’t to a += to it. Although it defeats the purpose of learning how do it the hard way, you can do it like this:
I understand that the compiler needs the expression to be known at compile time to compile a switch, but why isn’t Foo.BA_ constant? While they are constant from the perspective of any code that executes after the fields have been initialized, they are not a compile time constant in the sense required by the JLS; … Read more
From the api on GridLayout: The container is divided into equal-sized rectangles, and one component is placed in each rectangle. Try using FlowLayout or GridBagLayout for your set size to be meaningful. Also, @Serplat is correct. You need to use setPreferredSize( Dimension ) instead of setSize( int, int ).
Right Click on Project > Properties > Java Build Path > Add the Test folder as source folder. All source folders including Test Classes need to be in Eclipse Java Build Path. So that the sources such as main and test classes can be compiled into the build directory (Eclipse default folder is bin).
To map a composite key, you can use the EmbeddedId or the IdClass annotations. I know this question is not strictly about JPA but the rules defined by the specification also applies. So here they are: 2.1.4 Primary Keys and Entity Identity … A composite primary key must correspond to either a single persistent field or property or to a … Read more