- Are the imports checked for validity at compile time? e.g.will the code containing an import such as java.lang.ABCD compile?
Answer: Yes the imports are checked for the semantic validity at compile time.The code containing above line of import will not compile.It will throw an error saying,can not resolve symbolsymbol : class ABCDlocation: package ioimport java.io.ABCD;
- Does importing a package imports the subpackages as well? e.g.Does importing com.MyTest.* also import com.MyTest.UnitTests.*?
Answer: No you will have to import the subpackages explicitly.Importing com.MyTest.* will import classes in the package MyTest only.It will not import any class in any of it's subpackage.
- What is the difference between declaring a variable and defining a variable?
Answer: In declaration we just mention the type of the variable and it's name.We do not initialize it.But defining means declaration + initialization.e.g String s; is just a declaration while String s = new String ("abcd"); Or String s = "abcd"; are both definitions.
- What is the default value of an object reference declared as an instance variable?
Answer: null unless we define it explicitly.
- Can a level class be private or protected?
Answer: No.A level class can not be private or protected.It can have either "public" or no modifier.If it does not have a modifier it is supposed to have a default access.If a level class is declared as private the compiler will complain that the "modifier private is not allowed here".This means that a level class can not be private.Same is the case with protected.
- What type of parameter passing does Java support?
Answer: In Java the arguments are always passed by value.
- Primitive data types are passed by reference or pass by value?
Answer: Primitive data types are passed by value.
- Objects are passed by value or by reference?
Answer: Java only supports pass by value.With objects, the object reference itself is passed by value and so both the original reference and parameter copy both refer to the same object.
- What is serialization?
Answer: Serialization is a mechanism by which you can save the state of an object by converting it to a byte stream.
- How do I serialize an object to a file?
Answer: The class whose instances are to be serialized should implement an interface Serializable.Then you pass the instance to the ObjectOutputStream which is connected to a fileoutputstream.This will save the object to a file.
