Difference between Vector and ArrayList?
Vector
is synchronized whereas arraylist is not.
Difference between
Swing and Awt?
AWT
are heavy-weight components. Swings are light-weight components. Hence swing
works faster than AWT.
What is the
difference between a constructor and a method?
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.
What is an Iterator?
Some
of the collection classes provide traversal of their contents via a
java.util.Iterator interface. This interface allows you to walk through 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.
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.
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, i.e., without any
access modifier (i.e., public private or
protected).It means that it is visible to all within a particular package.
What is an abstract
class?
Abstract
class must be extended/sub-classed (to be useful). It serves as a template. A
class that is abstract may not be instantiated (i.e., 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.
What is static in
java?
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.
What is final?
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).
Source: Here
