Java what to learn

Every year or so I have a project in Java I learn enough thing to finish the project then I forget it by getting busy in other proejcts.
Over the years I really loved and hated Java,

Java what to learn:

• Ant: is a Java-based build tool. In theory, it is kind of like Make, without Make’s wrinkles and with the full portability of pure Java code.
• Tomcat: servlet and JSP server, can work as standalone, with Apache HTTPd, or IIS.
• log4j: log4j is a Java-based logging utility. It is used primarily as a debugging tool.
• JUnit: JUnit is a unit testing framework for the Java programming language.