如何在 Java 应用程序中测试私有构造函数? [英] How to test a private constructor in Java application?

问题描述

如果一个类包含一堆静态方法，为了确保没有人错误地初始化了这个类的实例，我做了一个私有构造函数:

If a class contains a bunch of static methods, in order to make sure no one by mistake initializes an instance of this class, I made a private constructor:

private Utils() {
}

现在..如何测试，因为无法看到构造函数?这可以完全覆盖测试吗?

Now .. how could this be tested, given that constructor can't be seen? Can this be test covered at all?

推荐答案

使用反射，您可以调用私有构造函数:

Using reflection, you can invoke a private constructor:

Constructor<Util> c = Utils.class.getDeclaredConstructor();
c.setAccessible(true);
Utils u = c.newInstance(); // Hello sailor

但是，您甚至可以做到这一点:

However, you can make even that not possible:

private Utils() {
    throw new UnsupportedOperationException();
}

通过在构造函数中抛出异常，您可以阻止所有尝试.

By throwing an exception in the constructor, you prevent all attempts.

我也会使类本身 final，只是因为":

public final class Utils {
    private Utils() {
        throw new UnsupportedOperationException();
    }
}

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