对象与静态方法设计 [英] Object vs static method design

问题描述

如下图所示，我可以通过两种简单的方式制作流式复印机（介绍Apache Commons或类似的）。我应该选择哪一个，以及为什么？

As shown below, there are two straightforward ways I could make a stream copier (bar introducing Apache Commons or similar). Which one should I go for, and why ?

public class StreamCopier {
private int bufferSize;

public StreamCopier() {
    this(4096);
}

public StreamCopier(int bufferSize) {
    this.bufferSize = bufferSize;
}

public long copy(InputStream in , OutputStream out ) throws IOException{
    byte[] buffer = new byte[bufferSize];
    int bytesRead;
    long totalBytes = 0;
    while((bytesRead= in.read(buffer)) != -1) {
        out.write(buffer,0,bytesRead);
        totalBytes += bytesRead;
    }

    return totalBytes;
}
}

vs

 public class StreamCopier {

 public static long copy(InputStream in , OutputStream out)
     throws IOException {
     return this.copy(in,out,4096);
 }

 public static long copy(InputStream in , OutputStream out,int bufferSize)
     throws IOException {
     byte[] buffer = new byte[bufferSize];
     int bytesRead;
     long totalBytes = 0;
     while ((bytesRead= in.read(buffer)) != -1) {
         out.write(buffer,0,bytesRead);
         totalBytes += bytesRead;
     }

     return totalBytes;
}
}

推荐答案

我使用非静态（实例）版本，并将其作为与setter的显式依赖关系提供给消费者：

I'd go with the non-static (instance) version, and supply it to consumers as an explicit dependency with a setter:

• 嘲笑它因此，单元测试的结果是微不足道的，因此消费者的测试不会与实现相结合;


• 交换功能非常简单，例如：使用子类;


• 与依赖注入系统很好地配合。

编辑

回应一个（有用的！）评论这有助于嘲笑？，这是它的工作方式：

In response to a (useful!) comment of "how does this help mocking?", here's how it might work:

class ThingThatUsesStreamCopier {

    // our copier instance. set in constructor, but might equally use
    // a setter for this:
    private StreamCopier copier;

    public ThingThatUsesStreamCopier(StreamCopier copier) {
        this.copier = copier;
    }

    public void makeCopy(Stream in, Stream out) {
        // probably something a little less trivial...
        copier.copy(in, out);
    }
}

当我来测试 ThingThatUsesStreamCopier ，我可以创建一个<$ c的模拟对象版本$ c> StreamCopier 并使用此模拟实例化 ThingThatUsesStreamCopier 。

When I come to test ThingThatUsesStreamCopier, I can create a mock object version of a StreamCopier and instantiate the ThingThatUsesStreamCopier using this mock.

这样做，我可以完全控制我的模拟行为，所以我的测试与 StreamCopier 的任何实际实现分离。我只测试消费者，而不是消费者和消费者。

By doing so, I have full control over the behaviour of my mock, so my test is decoupled from any real implementations of StreamCopier. I am only testing the consumer, not the consumer plus the consumed.

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