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- Question
How do you decide when to use HashMap and when to use TreeMap ?
- Correct Answer
- For inserting, deleting, and locating elements in a Map, the HashMap offers the best alternative If, however, you need to traverse the keys in a sorted order, then TreeMap is your better alternative Depending upon the size of your collection, it may be faster to add elements to a HashMap, then convert the map to a TreeMap for sorted key traversal
- 1. How are this() and super() used with constructors? Discuss
- 2. Just by seeing the signature of the bean how can you specity whether it is a Statefull of Stateless Session Bean? Discuss
- 3. Difference between Java Beans & Servlets? Discuss
- 4. try { int x = Integer.parseInt("two"); } Which could be used to create an appropriate catch block?
Options- A. ClassCastException
- B. IllegalStateException
- C. NumberFormatException
- D. None Discuss
- 5. class Hell { public static void main(String[] args) { Integer i = 42; String s = (i<40)?"life":(i>50)?"base":"ball"; System.out.println(s); } }
Options- A. null
- B. ball
- C. base
- D. None Discuss
- 6. What is the Dictionary class? Discuss
- 7. What is the common usage of serialization? What exceptions occur during serialization? Discuss
- 8. What is the purpose of garbage collection in Java, and when is it used ? Discuss
- 9. When is the finalize() called ? What is the purpose of finalization ? Discuss
- 10. What is Marker Interface? Discuss
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Correct Answer: Constructors use this to refer to another constructor in the same class with a different parameter list Constructors use super to invoke the superclass's constructor If a constructor uses super, it must use it in the first line; otherwise, the compiler will complain
Correct Answer: The create method in a stateless bean cannot have arguments, and can only have a single method called create() While create in Stateful bean can have arguments and could be any method starting with create string eg create(arg1, arg2, ) Although it is not compiler checked but in stateless bean the ejb Passivate() and ejb Active() methods has to be empty as these functions are never called by EJB container As conceptually in stateful session bean we might need to store the clients information hence arguments in createare necessary While in stateless bean we don't hence no arguments are necessary It's intutive isn't intutive isn't I my life I haven't seen such a futuristic server programming tool as EJB
Correct Answer: java bean is a reusable component, where as the servlet is the java program which extends the server capability
Correct Answer: NumberFormatException
Explanation:
C is correct. 'Integer.parseInt' can throw a NumberFormatException, and IllegalArgumentException is its superclass
Correct Answer: ball
Explanation:
D is correct. This is a ternary nested in a ternary with a little unboxing thrown in.Both of the ternary expressions are false.
Correct Answer: - The Dictionary class is an abstract class - Classes like Hashtable which map keys to values inherit from this class - An object can be looked for if a dictionary and a key is provided - Any non-null object can be used as a key and as a value
Correct Answer: The object need to be serialized when it?s sent over a network and when it?s state is saved Exceptions which occur during serialization are: a transient fields b when the base class is serialized then only base class fields are handled c static fields are ignored because they are not part of any state
Correct Answer: The purpose of garbage collection is to identify and discard those objects that are no longer needed by the application, in order for the resources to be reclaimed and reused
Correct Answer: The finalize method is called by the garbage collector, just before releasing the object?s memory It is normally advised to release resources held by the object inside the finalize method
Correct Answer: An interface without having any methods and by implementing that interface if our objects will get same ability such type interfaces are called marker interface (or) ability interface (or) tag interface
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