在抽象类中强制执行方法执行顺序(Enforce method execution order in Abstract Class)

 我有一个商业案例需要按顺序发生3件事情： 
 
 
 
 下载（） 
 
 
 处理（） 
 
 
 上传（） 
 
 
 现在，Abstract Class FileTransfer为1. downloadFiles（）和3. upload（）提供实现，但不提供2. process（） - 子类（如MusicFileTransfer或VideoFileTransfer或PDFFileTransfer）将在2.进程中执行不同的操作）阶段。 
 
 因此，抽象类似乎很清楚： 
 
public abstract class FileTransfer {

public void download() {
    // implementation provided
}

public abstract void process(); // implementation not provided

public void upload() {
    // implementation provided
}

}
 
 但是有一个问题 - MusicFileTransfer在下载（）或任何其他顺序之前调用process（）将永远 不会有好的时机。 该过程必须始终为1. download（），2. process（），然后3. upload（）。 
 
 所以我想像这样： 
 
public void doTransfer() {
    // private methods since we want to enforce this order of execution
    download(); // implem provided
    process(); // abstract method
    upload(); // implem provided
}
 
 在FileTransfer中包装这三个调用。 但为了让子类MusicFileTransfer覆盖process（）...它必须是public或protected（不是私有的）。 
 
 我应该如何解决这个泡菜？ 有一个公共的doTransfer（） 和一个公共进程（），只是确保process（）永远不会被调用？ 或者抛弃doTransfer（）并希望订单总是正确的？ 

I have a business case in which 3 things need to happen, in sequence:
 
 
 
download()
 
 
process()
 
 
upload()
 
 
Now, the Abstract Class FileTransfer provides implementation for 1. downloadFiles() and 3. upload(), but not 2. process() -- child classes (like MusicFileTransfer or VideoFileTransfer or PDFFileTransfer) will do different things in the 2. process() stage.
 
So it seems clear to make the abstract class like so:
 
public abstract class FileTransfer {

public void download() {
    // implementation provided
}

public abstract void process(); // implementation not provided

public void upload() {
    // implementation provided
}

}
 
But one issue -- There will never ever be a time in which it is okay for, say, MusicFileTransfer to call process() before download() or any other order. The process must always be 1. download(), 2. process(), then 3. upload().
 
So I imagine something like:
 
public void doTransfer() {
    // private methods since we want to enforce this order of execution
    download(); // implem provided
    process(); // abstract method
    upload(); // implem provided
}
 
in FileTransfer to wrap around these three calls. But in order for the child class MusicFileTransfer to override process() ... it must be public or protected (not private).
 
What should I do to work around this pickle? Have a public doTransfer() and a public process() and just make sure process() is never ever called? Or do away with the doTransfer() and hope that the order is always correct?

原文：https://stackoverflow.com/questions/26125721