The Java® Language Specification, Java SE 8 Edition

Chapter 18. Type Inference

A variety of compile-time analyses require reasoning about types that are not yet known. Principal among these are generic method applicability testing (§18.5.1) and generic method invocation type inference (§18.5.2). In general, we refer to the process of reasoning about unknown types as type inference.

At a high level, type inference can be decomposed into three processes:

• Reduction takes a compatibility assertion about an expression or type, called a constraint formula, and reduces it to a set of bounds on inference variables. Often, a constraint formula reduces to other constraint formulas, which must be recursively reduced. A procedure is followed to identify these additional constraint formulas and, ultimately, ...