What does upcasting mean?
Upcasting is a technical term most often used in object-oriented programming for converting a value or reference from a specific class or type into a more general one. For example, a program may upcast an ArrayList to a List, or a specialized object to a superclass. The conversion is generally considered safe because the resulting reference supports the broader set of operations defined by the target type. The word can also have a literal sense involving casting or projecting something upward. In programming discussions, upcasting is commonly contrasted with downcasting, which performs the opposite operation by converting a general reference into a more specific type. Outside computing, the word is comparatively uncommon and may appear in technical descriptions of casting processes or physical movement. Its usefulness lies in naming a clear and deliberate movement from specificity toward generality.
The conversion of a value or reference from a specific type or subclass to a more general type or superclass; more broadly, the act of casting something upward.
"The method returns a List, requiring an upcasting from the more specific collection type."
The computing sense is the dominant modern usage. In programming, it usually describes a type or reference conversion rather than a change in the underlying value.
To convert a value or reference to a more general type or superclass; less commonly, to cast or throw something upward.
"The code upcasts the subclass instance before passing it to the generic collection."
This form is chiefly used in programming and technical contexts.
Rare; upcasting is usually used as an uncountable process or activity.
"The report documented several separate upcastings of specialized references."
In programming, upcasting is a safe journey upward through a class hierarchy; in metalwork, it can mean literally casting something upward.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does upcasting come from?
The word is formed by combining up with cast, so its basic meaning is “casting upward.” The element cast derives from Old Norse kasta, meaning “to throw” or “to cast,” and is the same root found in words such as broadcast and forecast. In computing, upcasting developed as a metaphorical extension describing movement from a particular type or class to a broader one.
Related word forms
How upcasting is actually used
The computing sense is technical and especially common in object-oriented programming. The upward-casting sense is less frequent and may occur in specialist technical contexts. The term is not interchangeable with downcasting.
Easily confused with upcasting
Upcasting converts a value to a more general type, whereas downcasting converts it to a more specific type.