We want to emphasize that Sun has maintained
good compatibility among codes written with the different versions.
Generally, the newer versions maintain compatibilty with older
code. The approach has been to add new features without subtracting
any older features. (In some cases, such as the event
handling system introduced in Java 1.1, code using newer
classes and techniques should not be mixed in the same program
with older version code.)
Thus far, Java maintains backwards compatibility. A
program written according to Java 1.0 will compile with a Java
5 compiler. (Though some obsolete methods will generate "deprecation"
warning messages from the compiler.) The bytecode from a Java
1.0 compiler will still run in a Java 5 virtual machine.
Note: Running code in older
JVMs is a different matter. As of version 1.4, even when the
source code is compliant with version 1.1, you must explicitly
target the compiler output to 1.1 bytecode if you want it
to run with a version 1.1 JVM. That is,
javac -target 1.1 MyApplet.java
will allow this applet program to run with a 1.1 JVM.
You can in some cases run into problems if you mix code between
versions in the same program . For example, the handling of
events, such as mouse clicks, changed significantly from 1.0
to 1.1. A program can use either of the event handling approaches
but it cannot contain both.
We will mention compatibility issues as we encounter
We compiled our codes with Sun's version J2SE 5.0 compiler
and tested the programs with the 5.0 JVM . For the applet examples,
we assume the reader has installed the latest version of the
When you install the SDK, it will also install the Java plug-in
in the browsers it finds on your system.
Currently (circa 2004) many people are still using browsers
that only run applets compatible with Java 1.1 (i.e. the standard
JVM version installed in the IE browser is still for Java 1.1).
If your goal is to write applets for the broadest possible audience,
then you will need to write code limited to version 1.1 classes
and methods. In general, though, we recommend using the full
capabilities of Java 5.0 when writing applets for desktop PC
You can set up applet
tags in the web page to initiate the downloading of a plug-in
if it is not present. The simplest approach, though, is just
to tell visitors to your web pages with applets that if an applet
fails to run, they should install the plug-in by going to www.java.com
and clicking on the "Get It Now" button.
References & Web
Latest update: Oct.9.2004