@Delegate类没有默认构造函数 [英] @Delegate class without default constructor

问题描述

如何在Groovy中为没有默认构造函数的类创建委托类？我想装饰JUnit的ResultPrinter，但得到关于缺少构造函数的错误。

How can I create a delegate class in Groovy for a class which doesn't have a default constructor? I would like to decorate JUnit's ResultPrinter but am getting an error about the missing constructor.

推荐答案

我不明白你的问题。我只是用Java的 Short - 这也没有默认的构造函数。

I don't understand your issue. I just tried this with Java's Short — which also does not have a default constructor.

除非你没有初始化委托对象，否则你会得到一个NPE。

Everything worked as expected, except if you didn't initialize the delegated object, you get an NPE.

有可能你是使用 @Delegate 错误地？委托不会修饰现有的类，它允许您在自己的类中使用现有的类方法。它就像 extend ，但没有类继承。

Is it possible you are using @Delegate incorrectly? Delegate doesn't decorate existing classes, it allows you to use an existing classes methods in your own class. It's like extend, but without the class inheritance.

示例代码：

class Foo {
    @Delegate Short num
    String bar
    String toString() { "$bar: $num" }
}

def f = new Foo(bar: 'bob', num: 34 as Short)
println f // OK
println f.doubleValue() // OK

f = new Foo()
println f.doubleValue() // NPE

（或者，提供一些有用的信息，例如实际的错误和堆栈跟踪以及示例代码，将会为您提供更有用的响应。）

(Alternatively, providing some useful information, such as the actual error and stacktrace, and example code, will get you more useful responses.)

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