How would you improve performance of a Java application?

􀂃 Pool valuable system resources like threads, database connections, socket connections etc. Emphasise on
reuse of threads from a pool of threads. Creating new threads and discarding them after use can adversely
affect performance. Also consider using multi-threading in your single-threaded applications where possible to enhance performance. Optimze the pool sizes based on system and application specifications and
requirements.
􀂃 Optimize your I/O operations: use buffering  when writing to and reading from
files and/or streams. Avoid writers/readers if you are dealing with only ASCII characters. You can use streams instead, which are faster. Avoid premature flushing of buffers. Also make use of the performance and scalability enhancing features such as non-blocking and asynchronous I/O, mapping of file to memory etc
offered by the NIO (New I/O).
􀂃 Minimize network overheads by retrieving several related items simultaneously in one remote invocation if
possible. Remote method invocations involve a network round-trip, marshalling and unmarshalling of
parameters, which can cause huge performance problems if the remote interface is poorly designed.
􀂃 Establish whether you have a potential memory problem and manage your objects efficiently: remove
references to the short-lived objects from long-lived objects like Java collections etc (Refer Q64 in Java
section) to minimise any potential memory leaks. Also reuse objects where possible. It is cheaper to recycle
objects than creating new objects each time. Avoid creating extra objects unnecessarily. For example use
mutable StringBuffer/StringBuilder classes instead of immutable String objects in computation expensive
loops as discussed in Q17 in Java section. Automatic garbage collection is one of the most highly touted
conveniences of Java. However, it comes at a price. Creating and destroying objects occupies a significant
chunk of the JVM's time. Wherever possible, you should look for ways to minimise the number of objects
created in your code:
􀂃 If repeating code within a loop, avoid creating new objects for each iteration. Create objects before
entering the loop (i.e. outside the loop) and reuse them if possible.
􀂃 For complex objects that are used frequently, consider creating a pool of recyclable objects rather than
always instantiating new objects. This adds additional burden on the programmer to manage the pool,
but in select cases can represent an order of magnitude performance gain.
􀂃 Use lazy initialization when you want to distribute the load of creating large amounts of objects. Use lazy
initialization only when there is merit in the design.