Newinstance（）返回null [英] Newinstance() returning null

问题描述

尝试

{

URL url = file.toURI（）。toURL（）;

URL [] urls = new URL [] {url};

ClassLoader cl = new URLClassLoader（urls，ClockModel.class.getClassLoader（））;



Class<？> cls = Class.forName（pluginNamespace +。+ jar +。+ name，true，cl）;

Log.write（plugin object ====>+ cls） ;

等级<？扩展ClockModel> sub = cls.asSubclass（ClockModel.class）;

构造函数<？扩展ClockModel> ctor = sub.getConstructor（）;

model = ctor.newInstance（）;

}

catch（exception ex）

{

Log.write（Clock，Log.Severity.Error，无法创建插件对象：+ pluginNamespace +。+

jar +。+ name）;



Log.printException（ex）;



返回null ;

}



返回型号;

}



我尝试过：



model = ctor.newInstance（）;这是返回null。任何人都可以帮助

try
{
URL url = file.toURI().toURL();
URL[] urls = new URL[]{url};
ClassLoader cl = new URLClassLoader(urls, ClockModel.class.getClassLoader());

Class<?> cls = Class.forName(pluginNamespace + "." + jar + "." + name, true, cl);
Log.write("plugin object====>"+cls);
Class<? extends ClockModel> sub = cls.asSubclass(ClockModel.class);
Constructor<? extends ClockModel> ctor = sub.getConstructor();
model = ctor.newInstance();
}
catch(Exception ex)
{
Log.write("Clock", Log.Severity.Error, "Failed to create plugin object: " + pluginNamespace + "." +
jar + "." + name);

Log.printException(ex);

return null;
}

return model;
}

What I have tried:

model = ctor.newInstance(); this is returning null. Can anyone please help

推荐答案

不，因为我们无法运行你的代码 - 哎呀我们只有一小部分，而不是返回null的部分找出问题的唯一方法是在代码运行时查看它。



所以，这将取决于你。 />
幸运的是，您有一个可用的工具，它可以帮助您了解正在发生的事情：调试器。你如何使用它取决于你的编译器系统，但是一个快速的谷歌用于你的IDE名称和调试器应该给你你需要的信息。



放一个断点在函数的第一行，并通过调试器运行代码。然后查看您的代码，并查看您的数据并找出手动应该发生的事情。然后单步执行每一行检查您预期发生的情况正是如此。如果不是，那就是当你遇到问题时，你可以回溯（或者再次运行并仔细观察）以找出原因。


对不起，但我们不能为你做到这一点 - 时间让你学习一门新的（非常非常有用的）技能：调试！

No, because we can't run your code - heck we only have a tiny part of it, and not the part that returns the null And the only way to find out what is going on is to look at it while the code is running.

So, it's going to be up to you.
Fortunately, you have a tool available to you which will help you find out what is going on: the debugger. How you use it depends on your compiler system, but a quick Google for the name of your IDE and "debugger" should give you the info you need.

Put a breakpoint on the first line in the function, and run your code through the debugger. Then look at your code, and at your data and work out what should happen manually. Then single step each line checking that what you expected to happen is exactly what did. When it isn't, that's when you have a problem, and you can back-track (or run it again and look more closely) to find out why.

Sorry, but we can't do that for you - time for you to learn a new (and very, very useful) skill: debugging!

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