Why Data Types Are Important Data types are especially important in Java because it is a strongly typed language. This means that all operations are type-checked by the compiler for type compatibility. Illegal operations will not be compiled. Thus, strong type checking helps prevent errors and enhances reliability. To enable strong type checking, all variables, expressions, and values have atype. There is no concept of a “type-less” variable, for example. Furthermore, the type of a value determines what operations are allowedon it. An operation allowed on one type might not be allowed on another.