Long res2 = ((long) i1) + i2 // 64 bit signed arithmetic. Long res = i1 + i2 // 32 bit signed arithmetic. args).ĭoIt(foo) // passes foo as the argument arrayĭoIt((Object) foo) // passes new Object as the argument array.Ī third situation is when performing operations on primitive numeric types e.g. I'm not sure if this counts as an upcast (see JLS 5.1.13 last paragraph) but it should be mentioned anyway.Ī second situation involves varadic parameters: public void doIt(Object. The downcasting does not follow the is- a relation in most of the cases. It manually cast the base classs object to the derived classs object, so we must specify the explicit typecast. Where the code won't compile without the type cast. The Downcasting is an opposite process to the upcasting, which converts the base classs pointer or reference to the derived classs pointer or reference. Khi thc hin downcasting chng ta cn kim tra kiu d liu ca. If I have a String and I want to call the first overload rather than the second, I have to do this: String arg =. Upcasting l gn object ca subclass cho bin tham chiu supperclass, trong khi Downcasting gn object ca supperclass cho bin tham chiu subclass. suppose that we have overloaded methods: public void doIt(Object o). One situation where it is necessary to use upcasting in Java is when you want to force a specific method overload to be used e.g. However, there are situations where the presence of an explicit upcast changes the meaning of the statement / expression. (For a primitive type, an upcast results in a conversion, and can in some cases result in loss of precision e.g. This affects compile-time type checking and overload resolution, but not run-time behavior. The purpose of an implicit upcast (for a Java object type) is to "forget" static type information so that an object with a specific type can be used in a situation that requires a more general type. In your example, the explicit upcast Animal a = (Animal)d Ĭould be replaced with this: Animal a = d // implicit upcast The purpose of an implicit upcast (for a Java object type) is to 'forget' static type information so that an object with a specific type can be used in a situation that requires a more general type. In most situations, an explicit upcast is entirely unnecessary and has no effect.
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