Best programming approach/methodology to assure thread safety

Question

When I was learning Java coming from a background of some 20 years of procedural programming with basic, Pascal, COBOL and C, I thought at the time that the hardest thing about

Answer 1

1. Avoid sharing data between threads where possible (copy everything).
2. Never have locks on method calls to external objects, where possible.
3. Keep locks for the shortest amount of time possible.