java - 我创建的类可以自动装箱吗？

Question

有什么方法可以对我创建的类使用自动装箱吗？例如，我有这个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");
    }
}

现在，UnsignedInteger i = new UnsignedInteger(88);工作得很好，但是有什么办法可以编译：UnsignedInteger i = 88;？它不会适合我。提前致谢！

score 20 · Accepted Answer

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.

score 12 · Accepted Answer

12

不，不幸的是。自动装箱转换（根据JLS §5.1.7）仅为标准原始包装类定义。

于 2013-07-12T16:37:52.747 回答

score 1 · Accepted Answer

简而言之：不，这是不可能的。为此，您需要运算符重载，这在 Java 中不可用。见链接。

score 0 · Accepted Answer

如果您使用 Groovy，您可以通过实现 asBoolean 方法来设置布尔行为：http: //groovy-lang.org/semantics.html#_customizing_the_truth_with_asboolean_methods

例子：

class Color {
    String name

    boolean asBoolean(){
        name == 'green' ? true : false
    }
}

assert new Color(name: 'green')
assert !new Color(name: 'red')

我知道这不是纯 Java，而是编译为字节码并在 JVM 上运行。

java - 我创建的类可以自动装箱吗？

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