1) What are packages ? what is use of packages ?
Ans :The package statement defines a name space in which classes are stored.If you omit the package, the classes are put into the default package.
Signature... package pkg;
Use: * It specifies to which package the classes defined in a file belongs to. * Package is both naming and a visibility control mechanism.
2) What is difference between importing "java.applet.Applet" and "java.applet.*;" ?
Ans :"java.applet.Applet" will import only the class Applet from the package java.applet
Where as "java.applet.*" will import all the classes from java.applet package.
3) What do you understand by package access specifier?
Ans : public: Anything declared as public can be accessed from anywhere
private: Anything declared in the private can’t be seen outside of its class.
default: It is visible to subclasses as well as to other classes in the same package.
4) What is interface? What is use of interface?
Ans : It is similar to class which may contain method’s signature only but not bodies.
Methods declared in interface are abstract methods. We can implement many interfaces on a class which support the multiple inheritance.
5) Is it is necessary to implement all methods in an interface?
Ans : Yes. All the methods have to be implemented.
6) Which is the default access modifier for an interface method?
Ans : public.
7) Can we define a variable in an interface ?and what type it should be ?
Ans : Yes we can define a variable in an interface. They are implicitly final and static.
8) What is difference between interface and an abstract class?
Ans : All the methods declared inside an Interface are abstract. Where as abstract class must have at least one abstract method and others may be concrete or abstract.
In Interface we need not use the keyword abstract for the methods.
9) By default, all program import the java.lang package.
True/False
Ans : True
10) Java compiler stores the .class files in the path specified in CLASSPATH
environmental variable.
True/False
Ans : False
11) User-defined package can also be imported just like the standard packages.
True/False
Ans : True
12) When a program does not want to handle exception, the ______class is used.
Ans : Throws
13) The main subclass of the Exception class is _______ class.
Ans : RuntimeException
14) Only subclasses of ______class may be caught or thrown.
Ans : Throwable
15) Any user-defined exception class is a subclass of the _____ class.
Ans : Exception
16) The catch clause of the user-defined exception class should ______ its
Base class catch clause.
Ans : Exception
17) A _______ is used to separate the hierarchy of the class while declaring an
Import statement.
Ans : Package
18) All standard classes of Java are included within a package called _____.
Ans : java.lang
19) All the classes in a package can be simultaneously imported using ____.
Ans : *
20) Can you define a variable inside an Interface. If no, why? If yes, how?
Ans.: YES. final and static
