interview questions

• SOLID stands for:
• S: Single responsibility principle. a class should have only a single responsibility (i.e. only one potential change in the software's specification should be able to affect the specification of the class).
• O: Open/closed principle“software entities … should be open for extension, but closed for modification.”
• L: Liskov substitution principle “objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program.”
• I: Interface segregation principle  “many client-specific interfaces are better than one general-purpose interface"
• D: Dependency inversion principle.   one should “Depend upon Abstractions. Do not depend upon concretions".

Java EE applications commonly use distributed transactions to ensure the integrity of accesses to external resources. For example, distributed transactions allow multiple applications to perform atomic updates on the same database, and they allow a single application to perform atomic updates on multiple databases.

A thread is a single sequential flow of control within a program.

• Distributed transactions within the EJB container can be either of two kinds:
• Container-managed transactions: The EJB container controls the integrity of your transactions without your having to call commit or rollback. Container-managed transactions are recommended for Java EE applications that use the JMS API. You can specify appropriate transaction attributes for your enterprise bean methods.
• Bean-managed transactions: You can use these in conjunction with the javax.transaction.UserTransaction interface, which provides its own commit and rollback methods that you can use to delimit transaction boundaries. Bean-managed transactions are recommended only for those who are experienced in programming transactions.