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Is there any way to use autoboxing for the classes I create? For example, I have this subclass of Number.
public class UnsignedInteger extends Number { int n; public UnsignedInteger(int n) { if(n >= 0) this.n = n; else throw new IllegalArgumentException("Only positive integers are supported"); } } Now, UnsignedInteger i = new UnsignedInteger(88); works perfectly fine, but is there any way to make this compile : UnsignedInteger i = 88;? It won't for me. Thanks in advance!
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Autoboxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object wrapper classes. For example, converting an int to an Integer, a double to a Double, and so on. If the conversion goes the other way, this is called unboxing.
For example, converting int to Integer class. The Java compiler applies autoboxing when a primitive value is: Passed as a parameter to a method that expects an object of the corresponding wrapper class. Assigned to a variable of the corresponding wrapper class.
Autoboxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object wrapper classes. For example, converting an int to an Integer, a double to a Double, and so on. If the conversion goes the other way, this is called unboxing.
The automatic conversion of primitive data types into its equivalent Wrapper type is known as boxing and opposite operation is known as unboxing.
In short, no. There's no way to get that to compile.
Java only defines a limited set of pre-defined boxing conversions.
From the JLS, section 5.1.7:
Boxing conversion converts expressions of primitive type to corresponding expressions of reference type. Specifically, the following nine conversions are called the boxing conversions:
From type boolean to type Boolean
From type byte to type Byte
From type short to type Short
From type char to type Character
From type int to type Integer
From type long to type Long
From type float to type Float
From type double to type Double
From the null type to the null type
Additionally, one might think of overloading the = operator to perform this conversion, but operator overloading is not supported in Java, unlike in C++, where this would be possible.
So your conversion is not possible in Java.
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No, unfortunately. Automatic boxing conversions (as per JLS §5.1.7) are only defined for the standard primitive wrapper classes.
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