Phantom References
A phantom reference is an object that is wrapped inside
of a PhantomReference container. However, invoking the get() method
on a PhantomReference will always return null. A phantom reference
in conjunction with a reference queue provides a safer alternative to the
finalize()
method because there is no possibility of reviving a dead object
with new references.
Questions
How does the JVM divide memory on the heap?
What is the standard algorithm for garbage collection?
What are memory leaks? How can they be identified?
What are the four different types of references?
What is a ReferenceQueue?
Why is a phantom reference safer than using the finalize() method?
Java Database Connectivity
The Java Database Connectivity (JDBC) API is an interface for querying and
updating a database.
Connection
The Connection interface encapsulates the communication to a database.
A Connection is provided by either a DriverManager or a DataSource.
A DriverManager requires connection details such as the url and credentials,
but a DataSource hides the connection details behind an interface.
A DataSource is usually provided by an application server through a lookup
service called the Java Naming and Directory Interface (JNDI). DataSources
are preferable to DriverManagers because they are more flexible and easier
to change.
Statements
Statements
are provided by a Connection to encapsulate SQL queries.
PreparedStatements
are pre-compiled by the database and improve
performance for queries that are executed repeatedly or contain input
parameters. CallableStatements are used to execute stored procedures
that contain both input and output parameters.
ResultSets
ResultSets
are provided by Statements to encapsulate the result
of a query. A ResultSet contains a cursor that can scroll through rows and
extract type-safe values. ResultSets can be configured to support
bidirectional scrolling as well as row modifications depending on the capabilities
of the database.
SQL Injection
SQL injection is a popular attack vector that allows malicious queries to be
embedded into Statements that were constructed out of string
concatenations. SQL injection can be prevented by using
PreparedStatements
to register input values.
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