Only use it for legacy enterprise applications that are not exposed to the public internet.

If you absolutely need Java 1.4.0:

Java 2 Platform Standard Edition (J2SE) 1.4.0 , codenamed "Merlin," was a landmark release in Java's history, representing the first version developed under the Java Community Process

Downloading and running Java 1.4.0 in a modern environment poses significant security risks. This version does not contain the security patches developed over the last 20 years. Do not use Java 1.4.0 for web browsing.