Upgrade of legacy system from old Java version (1.3/1.4) to latest Java 8?

Question

I wanted to know what are the best practices/process to be followed if we are planning to migrate some legacy code in Java 1.3/1.4 to the latest version ie Java 8.

Answer 1

Lets first see what are the major changes from 1.3 to 1.8 in each version -

Java 8 (a.k.a 1.8)

Language changes:
lambda expressions (JSR 335, includes method handles)
continuation of Project Coin (small language improvements)
annotations on Java types
Library changes:
Improved Date and Time API

Java 7 (a.k.a 1.7)

Language changes:
Project Coin (small changes)
switch on Strings
try-with-resources
diamond operator

Library changes:
new abstracted file-system API (NIO.2) (with support for virtual filesystems)
improved concurrency libraries
elliptic curve encryption
more incremental upgrades

Platform changes:
support for dynamic languages

Java 6 (a.k.a 1.6)

Mostly incremental improvements to existing libraries, no new language features (except for the @Override snafu).

Java 5 (a.k.a 1.5)

Language Changes:
generics (that's the big one)
annotations
enum types
varargs, enhanced for loops (for-each)

Library changes:
concurrency utilities in java.util.concurrent

Java 1.4

Language changes:
the assert keyword

Library changes:
regular expressions support
NIO
integrated XML handling

Now coming to upgrade, Java is backward compatible so ideally you should not face any issue except the enum part which got changed from version 4 to 5 (rename any usages of the new enum keyword in the Java 4 code).