What are java static and instance blocks/Initializers?

 They're for two very different purposes:

• The static initializer block will be called on loading of the class, and will have no access to instance variables or methods.  it is often used to create static variables.
• The non-static initializer block on the other hand is created on object construction only, will have access to instance variables and methods, and will be called at the beginning of the constructor, after the super constructor has been called (either explicitly or implicitly) and before any other subsequent constructor code is called. I've seen it used when a class has multiple constructors and needs the same initialization code called for all constructors. Just as with constructors, you should avoid calling non-final methods in this block.
• So, to sum up, order of execution will be static block, instance block and then constructor.