Java Notes

Java Development Kit (JDK)

The most popular Java compiler is Sun's Software Development Kit (JDK) (aka Software Development Kit (SDK)). It's free, and does a good job. The only problem is that the compiler is only a compiler - there is no editor and no graphical user interface. It is typically used in one of the following ways.

Free Download

Download only the Java Standard Edition (SE) JDK from There are three editions - get the "standard edition", not the Enterprise Edition (EE) or Micro Edition (ME).

If you're a Macintosh user, it might already be installed on your system. Look at Java for Mac OS X.


Installing the JDK is easy (at least in Windows). Just follow the prompts.


If you're using commands from the DOS command window, you will probably have to set CLASSPATH. See CLASSPATH.

JVM runtime -enableassertions (-ea) option

java MyProgAssert statements are removed by class loader.
java -enableassertions MyProgAssert statements are executed.
java -ea MyProgShort form for allowing assertions.

It's also possible to enable/disable assertion checking at runtime for individual classes or for library routines, but that level of control is not useful for most purposes.