Java interview questions
1. What are synchronized methods and synchronized statements? Synchronized
methods are methods that are used to control access to an object. For example, a
thread only executes a synchronized method after it has acquired the lock for the
method’s object or class. Synchronized statements are similar to synchronized
methods. A synchronized statement can only be executed after a thread has
acquired the lock for the object or class referenced in the synchronized statement.
2. What are different ways in which a thread can enter the waiting state? A
thread can enter the waiting state by invoking its sleep() method, blocking on I/O,
unsuccessfully attempting to acquire an object’s lock, or invoking an object’s
wait() method. It can also enter the waiting state by invoking its (deprecated)
suspend() method.
3. Can a lock be acquired on a class? Yes, a lock can be acquired on a class. This
lock is acquired on the class’s Class object.
4. What’s new with the stop(), suspend() and resume() methods in new JDK
1.2? The stop(), suspend() and resume() methods have been deprecated in JDK
1.2.
5. What is the preferred size of a component? The preferred size of a component
is the minimum component size that will allow the component to display
normally.
6.
Welcome to
www.ewalkins.com
7. What method is used to specify a container’s layout? The setLayout() method
is used to specify a container’s layout. For example, setLayout(new
FlowLayout()); will be set the layout as FlowLayout.
8. Which containers use a FlowLayout as their default layout? The Panel and
Applet classes use the FlowLayout as their default layout.
9. What state does a thread enter when it terminates its processing? When a
thread terminates its processing, it enters the dead state.
10. What is the Collections API? The Collections API is a set of classes and
interfaces that support operations on collections of objects. One example of class
in Collections API is Vector and Set and List are examples of interfaces in
Collections API.
11. What is the List interface? The List interface provides support for ordered
collections of objects. It may or may not allow duplicate elements but the
elements must be ordered.
12. How does Java handle integer overflows and underflows? It uses those low
order bytes of the result that can fit into the size of the type allowed by the
operation.
13. What is the Vector class? The Vector class provides the capability to implement
a growable array of objects. The main visible advantage of this class is
programmer needn’t to worry about the number of elements in the Vector.
14. What modifiers may be used with an inner class that is a member of an outer
class? A (non-local) inner class may be declared as public, protected, private,
static, final, or abstract.
15. 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.
16. What is an Iterator interface? The Iterator interface is used to step through the
elements of a Collection.
17. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8
characters? Unicode requires 16 bits, ASCII require 7 bits (although the ASCII
character set uses only 7 bits, it is usually represented as 8 bits), UTF-8 represents
characters using 8, 16, and 18 bit patterns, UTF-16 uses 16-bit and larger bit
patterns
18. What is the difference between yielding and sleeping? Yielding means a thread
returning to a ready state either from waiting, running or after creation, where as
sleeping refers a thread going to a waiting state from running state. With reference
to Java, when a task invokes its yield() method, it returns to the ready state and
when a task invokes its sleep() method, it returns to the waiting state
19. What are wrapper classes? Wrapper classes are classes that allow primitive
types to be accessed as objects. For example, Integer, Double. These classes
contain many methods which can be used to manipulate basic data types
Does garbage collection guarantee that a program will not run out of memory? No,
it doesn’t. It is possible for programs to use up memory resources faster than they are
garbage collected. It is also possible for programs to create
Welcome to
www.ewalkins.com
20. objects that are not subject to garbage collection. The main purpose of Garbage
Collector is recover the memory from the objects which are no longer required
when more memory is needed.
21. Name Component subclasses that support painting? The following classes
support painting: Canvas, Frame, Panel, and Applet.
22. What is a native method? A native method is a method that is implemented in a
language other than Java. For example, one method may be written in C and can
be called in Java.
23. How can you write a loop indefinitely?
for(;;) //for loop
while(true); //always true
24. Can an anonymous class be declared as implementing an interface and
extending a class? An anonymous class may implement an interface or extend a
superclass, but may not be declared to do both.
25. What is the purpose of finalization? The purpose of finalization is to give an
unreachable object the opportunity to perform any cleanup processing before the
object is garbage collected. For example, closing a opened file, closing a opened
database Connection.
26. What invokes a thread’s run() method? After a thread is started, via its start()
method or that of the Thread class, the JVM invokes the thread’s run() method
when the thread is initially executed.
27. What is the GregorianCalendar class? The GregorianCalendar provides support
for traditional Western calendars.
28. What is the SimpleTimeZone class? The SimpleTimeZone class provides
support for a Gregorian calendar.
29. What is the Properties class? The properties class is a subclass of Hashtable that
can be read from or written to a stream. It also provides the capability to specify a
set of default values to be used.
30. What is the purpose of the Runtime class? The purpose of the Runtime class is
to provide access to the Java runtime system.
31. What is the purpose of the System class? The purpose of the System class is to
provide access to system resources.
32. What is the purpose of the finally clause of a try-catch-finally statement? The
finally clause is used to provide the capability to execute code no matter whether
or not an exception is thrown or caught. For example,
try
{
//some statements
}
catch
{
// statements when exception is cought
}
finally
{
//statements executed whether exception occurs or not
}
33. What is the Locale class? The Locale class is used to tailor program output to
the conventions of a particular geographic, political, or cultural region.
34. What must a class do to implement an interface? It must provide all of the
methods in the interface and identify the interface in its implements clause.
Welcome to
www.ewalkins.com
For Latest Updated Job Alerts Join This Group. We Will Send Latest Updated Jobs Information’s Directly To In Your Inbox
Source: – www.ewalkins.com
