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Java Interview Questions and Answers
Can applets communicate with each other?
At this point in time applets may communicate with other applets running
in the same virtual machine. If the applets are of the same class, they
can communicate via shared static variables. If the applets are of
different classes, then each will need a reference to the same class
with static variables. In any case the basic idea is to pass the
information back and forth through a static variable.
An applet can also get references to all other applets on the same page
using the getApplets() method of java.applet.AppletContext. Once you get
the reference to an applet, you can communicate with it by using its
public members.
It is conceivable to have applets in different virtual machines that
talk to a server somewhere on the Internet and store any data that needs
to be serialized there. Then, when another applet needs this data, it
could connect to this same server. Implementing this is non-trivial.
What are the steps in the JDBC connection?
While making a JDBC connection we go through the following steps :
Step 1 : Register the database driver by using :
Class.forName(\" driver classs for that specific database\" );
Step 2 : Now create a database connection using :
Connection con = DriverManager.getConnection(url,username,password);
Step 3: Now Create a query using :
Statement stmt = Connection.Statement(\"select * from TABLE NAME\");
Step 4 : Exceute the query :
stmt.exceuteUpdate();
How does a try statement determine which catch clause should be used to
handle an exception?
When an exception is thrown within the body of a try statement, the
catch clauses of the try statement are examined in the order in which
they appear. The first catch clause that is capable of handling the
exceptionis executed. The remaining catch clauses are ignored.
Can an unreachable object become reachable again?
An unreachable object may become reachable again. This can happen when
the object's finalize() method is invoked and the object performs an
operation which causes it to become accessible to reachable objects.
What method must be implemented by all threads?
All tasks must implement the run() method, whether they are a subclass
of Thread or implement the Runnable interface.
What are synchronized methods and synchronized statements?
Synchronized methods are methods that are used to control access to an
object. 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.
What is Externalizable?
Externalizable is an Interface that extends Serializable Interface. And
sends data into Streams in Compressed Format. It has two methods,
writeExternal(ObjectOuput out) and readExternal(ObjectInput in)
What modifiers are allowed for methods in an Interface?
Only public and abstract modifiers are allowed for methods in
interfaces.
What are some alternatives to inheritance?
Delegation is an alternative to inheritance. Delegation means that you
include an instance of another class as an instance variable, and
forward messages to the instance. It is often safer than inheritance
because it forces you to think about each message you forward, because
the instance is of a known class, rather than a new class, and because
it doesn't force you to accept all the methods of the super class: you
can provide only the methods that really make sense. On the other hand,
it makes you write more code, and it is harder to re-use (because it is
not a subclass).
What does it mean that a method or field is "static"?
Static variables and methods are instantiated only once per class. In
other words they are class variables, not instance variables. If you
change the value of a static variable in a particular object, the value
of that variable changes for all instances of that class.
Static methods can be referenced with the name of the class rather than
the name of a particular object of the class (though that works too).
That's how library methods like System.out.println() work out is a
static field in the java.lang.System class.
What is the difference between preemptive scheduling and time slicing?
Under preemptive scheduling, the highest priority task executes until it
enters the waiting or dead states or a higher priority task comes into
existence. Under time slicing, a task executes for a predefined slice of
time and then reenters the pool of ready tasks. The scheduler then
determines which task should execute next, based on priority and other
factors.
What is the catch or declare rule for method declarations?
If a checked exception may be thrown within the body of a method, the
method must either catch the exception or declare it in its throws
clause.
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