Java programming skills are in high demand for both enterprise development and Android mobile development roles.
The Robert Half Technology Salary Guide lists the salary midpoint for a developer/programmer analyst at $103,000 per year. Keep in mind that the local economy and cost of living can affect compensation, as well as industry, level of experience and skill set. View source
Use resources for design pattern and solid principals.
You can hack in Java at TopCoder, Inc. | Home of the world’s largest development community.
For relatively easier questions, you can start at HackerRank.
For some numerical algorithms, you can try Project Euler.
The attitude of a Java Programmer should not be to build logic, but to find the suitable class and method for your project from the whole bunch of Java API and make use of it.
Data structures, algorithms, and networking are important. OS can be additional.
Re:Make 