36: What if the main method is declared as private?
A: The program compiles properly but at runtime it will give "Main method not public." message.
37: What if the static modifier is removed from the signature of the main method?
A: Program compiles. But at runtime throws an error "NoSuchMethodError".
38: What if I write static public void instead of public static void?
A: Program compiles and runs properly.
39: What if I do not provide the String array as the argument to the method?
A: Program compiles but throws a runtime error "NoSuchMethodError".
40: What is the first argument of the String array in main method?
A: The String array is empty. It does not have any element. This is unlike C/C++ where the first element by default is the program name.
Showing posts with label collection. Show all posts
Showing posts with label collection. Show all posts
Friday, May 2, 2008
Java Interview Questions 7
31: What is an Iterators?
A: Some of the collection classes provide traversal of their contents via a java.util.Iterator interface. This interface allows you to walk a collection of objects, operating on each object in turn. Remember when using Iterators that they contain a snapshot of the collection at the time the Iterator was obtained; generally it is not advisable to modify the collection itself while traversing an Iterator.
32: State the significance of public, private, protected, default modifiers both singly and in combination and state the effect of package relationships on declared items qualified by these modifiers.
A: public : Public class is visible in other packages, field is visible everywhere (class must be public too)
private : Private variables or methods may be used only by an instance of the same class that declares the variable or method, A private feature may only be accessed by the class that owns the feature.
protected : Is available to all classes in the same package and also available to all subclasses of the class that owns the protected feature.This access is provided even to subclasses that reside in a different package from the class that owns the protected feature.
default :What you get by default ie, without any access modifier (ie, public private or protected).It means that it is visible to all within a particular package.
33: What is an abstract class?
A: Abstract class must be extended/subclassed (to be useful). It serves as a template. A class that is abstract may not be instantiated (ie, you may not call its constructor), abstract class may contain static data. Any class with an abstract method is automatically abstract itself, and must be declared as such.
A class may be declared abstract even if it has no abstract methods. This prevents it from being instantiated.
34: What is static in java?
A: Static means one per class, not one for each object no matter how many instance of a class might exist. This means that you can use them without creating an instance of a class.Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object. A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final. However, you can't override a static method with a nonstatic method. In other words, you can't change a static method into an instance method in a subclass.
35: What is final?
A: A final class can't be extended ie., final class may not be subclassed. A final method can't be overridden when its class is inherited. You can't change value of a final variable (is a constant).
A: Some of the collection classes provide traversal of their contents via a java.util.Iterator interface. This interface allows you to walk a collection of objects, operating on each object in turn. Remember when using Iterators that they contain a snapshot of the collection at the time the Iterator was obtained; generally it is not advisable to modify the collection itself while traversing an Iterator.
32: State the significance of public, private, protected, default modifiers both singly and in combination and state the effect of package relationships on declared items qualified by these modifiers.
A: public : Public class is visible in other packages, field is visible everywhere (class must be public too)
private : Private variables or methods may be used only by an instance of the same class that declares the variable or method, A private feature may only be accessed by the class that owns the feature.
protected : Is available to all classes in the same package and also available to all subclasses of the class that owns the protected feature.This access is provided even to subclasses that reside in a different package from the class that owns the protected feature.
default :What you get by default ie, without any access modifier (ie, public private or protected).It means that it is visible to all within a particular package.
33: What is an abstract class?
A: Abstract class must be extended/subclassed (to be useful). It serves as a template. A class that is abstract may not be instantiated (ie, you may not call its constructor), abstract class may contain static data. Any class with an abstract method is automatically abstract itself, and must be declared as such.
A class may be declared abstract even if it has no abstract methods. This prevents it from being instantiated.
34: What is static in java?
A: Static means one per class, not one for each object no matter how many instance of a class might exist. This means that you can use them without creating an instance of a class.Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object. A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final. However, you can't override a static method with a nonstatic method. In other words, you can't change a static method into an instance method in a subclass.
35: What is final?
A: A final class can't be extended ie., final class may not be subclassed. A final method can't be overridden when its class is inherited. You can't change value of a final variable (is a constant).
Java Interview Questions 6
25: What are pass by reference and passby value?
A: Pass By Reference means the passing the address itself rather than passing the value. Passby Value means passing a copy of the value to be passed.
26: What is HashMap and Map?
A: Map is Interface and Hashmap is class that implements that.
27: Difference between HashMap and HashTable?
A: The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. (HashMap allows null values as key and value whereas Hashtable doesnt allow). HashMap does not guarantee that the order of the map will remain constant over time. HashMap is non synchronized and Hashtable is synchronized.
28: Difference between Vector and ArrayList?
A: Vector is synchronized whereas arraylist is not.
29: Difference between Swing and Awt?
A: AWT are heavy-weight componenets. Swings are light-weight components. Hence swing works faster than AWT.
30: What is the difference between a constructor and a method?
A: A constructor is a member function of a class that is used to create objects of that class. It has the same name as the class itself, has no return type, and is invoked using the new operator.
A method is an ordinary member function of a class. It has its own name, a return type (which may be void), and is invoked using the dot operator.
A: Pass By Reference means the passing the address itself rather than passing the value. Passby Value means passing a copy of the value to be passed.
26: What is HashMap and Map?
A: Map is Interface and Hashmap is class that implements that.
27: Difference between HashMap and HashTable?
A: The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. (HashMap allows null values as key and value whereas Hashtable doesnt allow). HashMap does not guarantee that the order of the map will remain constant over time. HashMap is non synchronized and Hashtable is synchronized.
28: Difference between Vector and ArrayList?
A: Vector is synchronized whereas arraylist is not.
29: Difference between Swing and Awt?
A: AWT are heavy-weight componenets. Swings are light-weight components. Hence swing works faster than AWT.
30: What is the difference between a constructor and a method?
A: A constructor is a member function of a class that is used to create objects of that class. It has the same name as the class itself, has no return type, and is invoked using the new operator.
A method is an ordinary member function of a class. It has its own name, a return type (which may be void), and is invoked using the dot operator.
Java Interview Questions 5
21: What is the difference between an Interface and an Abstract class?
A: An abstract class can have instance methods that implement a default behavior. An Interface can only declare constants and instance methods, but cannot implement default behavior and all methods are implicitly abstract. An interface has all public members and no implementation. An abstract class is a class which may have the usual flavors of class members (private, protected, etc.), but has some abstract methods.
22: What is the purpose of garbage collection in Java, and when is it used?
A: The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources can be reclaimed and reused. A Java object is subject to garbage collection when it becomes unreachable to the program in which it is used.
23: Describe synchronization in respect to multithreading.
A: With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchonization, it is possible for one thread to modify a shared variable while another thread is in the process of using or updating same shared variable. This usually leads to significant errors.
24: Explain different way of using thread?
A: The thread could be implemented by using runnable interface or by inheriting from the Thread class. The former is more advantageous, 'cause when you are going for multiple inheritance..the only interface can help.
25: What are pass by reference and passby value?
A: Pass By Reference means the passing the address itself rather than passing the value. Passby Value means passing a copy of the value to be passed.
A: An abstract class can have instance methods that implement a default behavior. An Interface can only declare constants and instance methods, but cannot implement default behavior and all methods are implicitly abstract. An interface has all public members and no implementation. An abstract class is a class which may have the usual flavors of class members (private, protected, etc.), but has some abstract methods.
22: What is the purpose of garbage collection in Java, and when is it used?
A: The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources can be reclaimed and reused. A Java object is subject to garbage collection when it becomes unreachable to the program in which it is used.
23: Describe synchronization in respect to multithreading.
A: With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchonization, it is possible for one thread to modify a shared variable while another thread is in the process of using or updating same shared variable. This usually leads to significant errors.
24: Explain different way of using thread?
A: The thread could be implemented by using runnable interface or by inheriting from the Thread class. The former is more advantageous, 'cause when you are going for multiple inheritance..the only interface can help.
25: What are pass by reference and passby value?
A: Pass By Reference means the passing the address itself rather than passing the value. Passby Value means passing a copy of the value to be passed.
Java Interview Questions 4
16: Can a vector contain heterogenous objects?
A: Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.
17: Can a ArrayList contain heterogenous objects?
A: Yes a ArrayList can contain heterogenous objects. Because a ArrayList stores everything in terms of Object.
18: What is an enumeration?
A: An enumeration is an interface containing methods for accessing the underlying data structure from which the enumeration is obtained. It is a construct which collection classes return when you request a collection of all the objects stored in the collection. It allows sequential access to all the elements stored in the collection.
19: Considering the basic properties of Vector and ArrayList, where will you use Vector and where will you use ArrayList?
A: The basic difference between a Vector and an ArrayList is that, vector is synchronized while ArrayList is not. Thus whenever there is a possibility of multiple threads accessing the same instance, one should use Vector. While if not multiple threads are going to access the same instance then use ArrayList. Non synchronized data structure will give better performance than the synchronized one.
20: Can a vector contain heterogenous objects?
A: Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.
A: Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.
17: Can a ArrayList contain heterogenous objects?
A: Yes a ArrayList can contain heterogenous objects. Because a ArrayList stores everything in terms of Object.
18: What is an enumeration?
A: An enumeration is an interface containing methods for accessing the underlying data structure from which the enumeration is obtained. It is a construct which collection classes return when you request a collection of all the objects stored in the collection. It allows sequential access to all the elements stored in the collection.
19: Considering the basic properties of Vector and ArrayList, where will you use Vector and where will you use ArrayList?
A: The basic difference between a Vector and an ArrayList is that, vector is synchronized while ArrayList is not. Thus whenever there is a possibility of multiple threads accessing the same instance, one should use Vector. While if not multiple threads are going to access the same instance then use ArrayList. Non synchronized data structure will give better performance than the synchronized one.
20: Can a vector contain heterogenous objects?
A: Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.
Java Interview Questions 3
11: What is the Collection interface?
A: The Collection interface provides support for the implementation of a mathematical bag - an unordered collection of objects that may contain duplicates.
12: What is the Set interface?
A: The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.
13: What is the typical use of Hashtable?
A: Whenever a program wants to store a key value pair, one can use Hashtable.
14: I am trying to store an object using a key in a Hashtable. And some other object already exists in that location, then what will happen? The existing object will be overwritten? Or the new object will be stored elsewhere?
A: The existing object will be overwritten and thus it will be lost.
15: What is the difference between the size and capacity of a Vector?
A: The size is the number of elements actually stored in the vector, while capacity is the maximum number of elements it can store at a given instance of time.
A: The Collection interface provides support for the implementation of a mathematical bag - an unordered collection of objects that may contain duplicates.
12: What is the Set interface?
A: The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.
13: What is the typical use of Hashtable?
A: Whenever a program wants to store a key value pair, one can use Hashtable.
14: I am trying to store an object using a key in a Hashtable. And some other object already exists in that location, then what will happen? The existing object will be overwritten? Or the new object will be stored elsewhere?
A: The existing object will be overwritten and thus it will be lost.
15: What is the difference between the size and capacity of a Vector?
A: The size is the number of elements actually stored in the vector, while capacity is the maximum number of elements it can store at a given instance of time.
Thursday, May 1, 2008
Java Interview Questions 2
6: What is the GregorianCalendar class?
A: The GregorianCalendar provides support for traditional Western calendars
7: What is the Locale class?
A: The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region .
8: What is the SimpleTimeZone class?
A: The SimpleTimeZone class provides support for a Gregorian calendar .
9: What is the Map interface?
A: The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.
10: What is the highest-level event class of the event-delegation model?
A: The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy.
A: The GregorianCalendar provides support for traditional Western calendars
7: What is the Locale class?
A: The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region .
8: What is the SimpleTimeZone class?
A: The SimpleTimeZone class provides support for a Gregorian calendar .
9: What is the Map interface?
A: The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.
10: What is the highest-level event class of the event-delegation model?
A: The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy.
Java Interview Questions I
1: What is the Collections API?
A: The Collections API is a set of classes and interfaces that support operations on collections of objects.
2: What is the List interface?
A: The List interface provides support for ordered collections of objects.
3: What is the Vector class?
A: The Vector class provides the capability to implement a growable array of objects.
4: What is an Iterator interface?
A: The Iterator interface is used to step through the elements of a Collection .
5: Which java.util classes and interfaces support event handling?
A: The EventObject class and the EventListener interface support event processing.
A: The Collections API is a set of classes and interfaces that support operations on collections of objects.
2: What is the List interface?
A: The List interface provides support for ordered collections of objects.
3: What is the Vector class?
A: The Vector class provides the capability to implement a growable array of objects.
4: What is an Iterator interface?
A: The Iterator interface is used to step through the elements of a Collection .
5: Which java.util classes and interfaces support event handling?
A: The EventObject class and the EventListener interface support event processing.
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