Java JDBC Transaction Isolation Levels

Generally speaking, as the isolation levels become more restrictive, the performance of the system decreases because transactions are prevented from accessing the same data. If isolation levels are very restrictivein other words, if they are at the Serializable levelthen all transactions, even simple reads, must wait in line to execute. This can result in a system that is very slow. J2EE server that process a large number of concurrent transactions and need to be very fast will therefore avoid the Serializable isolation level where it is not necessary.

Read Uncommitted
The transaction can read uncommitted data (i.e., data changed by a different transaction that is still in progress). Dirty reads, nonrepeatable reads, and phantom reads can occur. Bean methods with this isolation level can read uncommitted changes.

Read Committed
The transaction cannot read uncommitted data; data that is being changed by a different transaction cannot be read. Dirty reads are prevented; nonrepeatable reads and phantom reads can occur. Bean methods with this isolation level cannot read uncommitted data.

Repeatable Read
The transaction cannot change data that is being read by a different transaction. Dirty reads and nonrepeatable reads are prevented; phantom reads can occur. Bean methods with this isolation level have the same restrictions as those in the Read Committed level and can execute only repeatable reads.

Serializable
The transaction has exclusive read and update privileges; different transactions can neither read nor write to the same data. Dirty reads, nonrepeatable reads, and phantom reads are prevented. This isolation level is the most restrictive.

Note: J2EE Isolation level on connections used by CMP beans
In a EJB 2.x or EJB 3.0 module, when a CMP bean uses a new data source to access a backend database, the isolation level is determined by J2EE Application Server run time, based on the type of access intent assigned to the bean or the calling method. Other non-CMP connection users can access this same data source and also use the access intent and application profile support to manage their concurrency control.

How to create a ZIP File

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Java Threading/ Multithreading Interview Questions with Answers

Describe synchronization in respect to multithreading.

Ans: 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.


Explain different way of using thread?

Ans: 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.


What are the two types of multitasking?

Ans :

1.process-based

2.Thread-based

What are the two ways to create the thread?

Ans :

1.by implementing Runnable

2.by extending Thread

What is the signature of the constructor of a thread class?

Ans : Thread(Runnable threadob,String threadName)

What are all the methods available in the Runnable Interface?

Ans : run()

What is the data type for the method isAlive() and this method is available in which class?

Ans : boolean, Thread

What are all the methods available in the Thread class?

Ans :

1.isAlive()

2.join()

3.resume()

4.suspend()

5.stop()

6.start()

7.sleep()

8.destroy()

What are all the methods used for Inter Thread communication and what is the class in which these methods are defined?

Ans :

1. wait(),notify() & notifyall()

2. Object class

What is the mechanisam defind by java for the Resources to be used by only one Thread at a time?

Ans : Synchronisation

What is the procedure to own the moniter by many threads?

Ans : not possible

What is the unit for 1000 in the below statement?

ob.sleep(1000)

Ans : long milliseconds

What is the data type for the parameter of the sleep() method?

Ans : long

What are all the values for the following level?

max-priority

min-priority

normal-priority

Ans : 10,1,5

What is the method available for setting the priority?

Ans : setPriority()

What is the default thread at the time of starting the program?

Ans : main thread

The word synchronized can be used with only a method.

True/ False

Ans : False

Which priority Thread can prompt the lower primary Thread?

Ans : Higher Priority

How many threads at a time can access a monitor?

Ans : one

What are all the four states associated in the thread?

Ans : 1. new 2. runnable 3. blocked 4. dead

The suspend()method is used to teriminate a thread?

True /False

Ans : False

The run() method should necessary exists in clases created as subclass of thread?

True /False

Ans : True

When two threads are waiting on each other and can't proceed the programe is said to be in a deadlock?

True/False

Ans : True

Which method waits for the thread to die ?

Ans : join() method

Which of the following is true?

1) wait(),notify(),notifyall() are defined as final & can be called only from with in a synchronized method

2) Among wait(),notify(),notifyall() the wait() method only throws IOException

3) wait(),notify(),notifyall() & sleep() are methods of object class

1
2
3
1 & 2
1,2 & 3
Ans : D

Garbage collector thread belongs to which priority?

Ans : low-priority

What is meant by timeslicing or time sharing?

Ans : Timeslicing is the method of allocating CPU time to individual threads in a priority schedule.

What is meant by daemon thread? In java runtime, what is it's role?

Ans : Daemon thread is a low priority thread which runs intermittently in the background doing the garbage collection operation for the java runtime system.