And yet it is so simple to do those improvements while developing applications. One of them is not to use import package.*; and only include the packages you really need. This may sound so simple but I doubt many people think about this when developing applications. I have often heard (and yes i have done that mistake myself recently) people say stuff like “I cant be bothered with every single include, i rather just include everything” and “It doesnt really matter”.

And to be all honest – it is true when developing small applicationsm that do not require to be run for a very long time without destroying the VM (a.k.a restarting the application). But in the long run – the more classes you are importing, the more PermGen memory is used — and that is a waste when you do not need so many classes.

So here is a first and really basic optimization suggestion:

Try avoiding importing * packages as much as possible. I do realize that it may not always be easy to do and your code may become a few hundered lines larger — but in the long run you will not regret it!

Now a fast numbers to prove my point

Unoptimized application PermGen usage:14.5Mb With the following * imports:

import java.util.*;
import java.io.*;
import java.sql.*;

Optimized application PermGen usage: 10.2Mb When replaced * imports with in somewhat 30 classes:

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Timestamp;
import java.util.Date;
import java.util.Iterator;
import java.util.Vector;

As you can see numbers speak for themselves – that is quite an optimization