Core Java Question List #7

1. Does a class inherit the constructors of its superclass?

A class does not inherit constrcutors from any of its superclass.

2. Name the eight primitive Java Types.

The eight primitive types are byte, char, short, int, long, float, double, and Boolean.

3. What restrictions are placed on the values of each case of a switch statement?

During compilation, the values of each case of a switch statement must evaluate to a value that can be prompted to an int value.

4. What is the difference between a while statement and a do while statement?

A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do while statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do while statement will always execute the body of a loop at least once.

5. What modifiers can be used with a local inner class?

A local inner class may be final or abstract.

6. When does the compiler supply a default constructor for a class?

The compiler supplies a default constructor for a class if no other constructors are provided.

7. If a method is declared as protected, where may the method be accessed?

A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared.

8. What are the legal operands of the instanceof operator?

The left operand is an object reference or null value and the right operand is a class, interface, or array type.

9. Are true and false keywords?

The values true and false are not keywords.

10. What happens when you add a double value to a String?

The result is a string object.

11. What is the difference between inner class and nested class?

When a class is defined within a scope of another class, then it becomes inner class. If the access modifier of the inner class is static, then it becomes nested class.

12. Can an abstract class be final?

An abstract class may not be declared as final.

13. What is numeric promotion?

Numeric promotion is the conversion of a smaller numeric type to a larger numeric type, so that interger and floating-point operations may take place. In numerical promotion, byte, char,and short values are converted to int values. The int values are also converted to long values, if necessary, the long and float values are converted to double values, as required.

14. What is the difference between a public and a non-public class?

A public class may be accessed outside of its package. A non-public class may not be accessed outside of its package.

15. To what value is a variable of the Boolean type automatically initialized?

false

16. What is the difference between the prefix and postfix forms of the ++ operator?

The prefix form performs the increment operation and returns the value of the increment operation. The postfix form returns the current value all of the expression and then performs the increment operation on that value.

17. What restrictions are placed on method overriding?

Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overriding method.

18. What is the java package and how is it used?

A java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.

19. What modifiers may be used with a top-level class?

A top-level class may be public, abstract, or final.

20. What is the difference between an if statement and a switch statement?

The if statement is used to select among two alternatives. It uses a Boolean expression to decide which alternative should be executed. The switch statement is used to select among multiple alternatives. It used an int expression to determine which alternative should be executed.

21. What are the practical benefits, if any, of importing a specific class rather than an entire package (e.g. import java.net.* versus import java.net.Socket)?

It makes no difference in the generated class files since only the classes that are actually used are referenced by the generated class file. There is another practical benefit to importing single classes, and this arises when two ( or more) packages have classes with the same name. Take java.util.Timer and javax.swing.Timers, for example, if I import java.util.* and javax.swing.* and then try to use “Timer”, I get an error while compiling (the class name is ambiguous between both packages). Let’s say what you really wanted was the javax.swing.Timer class, and the only classes you plan on using in java.util are Collection and HashMap. In this case, some people will prefer to import java.util.Collection and import java.util.HashMap instead of importing java.util.*. This will now allow them to use Timer, Collection, HashMap, and other javax.swing classes without using fully qualified class names in.

22. Can a method be overloaded based on different return type but same argument type?

No, because the methods can be called without using their return type in which case there is ambiquity for the compiler.

23. What happens to a static variable that is defined within a method of a class?

Can’t do it. You’ll get a compilation error.