使用反射来迭代类成员

Question

I have a class with numerous parameters of various types. I want to iterate over all type A members , and run a specific functions ( A.doSomething() )

This doesn't even compile: The conversion from field to XPathDataElement is illegal

Field[] fields = this.getClass().getDeclaredFields();
  for (Field field : fields) {
     if (field. getType().getName().equals(XPathDataElement.class.getName()))
        {               
                tmp = (XPathDataElement)field; // Doesn't compile
                sb.append(field.getName() + ":"); 
                tmp.update();
        }
    }

Thanks!

Answer 1

It's hard to debug your code when you don't say what's wrong with it.

Two things I can see:

1. There's no need to compare strings to decide if the field's type is the right class.

    if (field.getType().equals(XPathDataElement.class)) 

   should work.

   Edit: Steve Reed points out that you don't necessarily need it to be exactly XPathDataElement ; a subclass will work just as well. To check if the field can be treated as an XPathDataElement , you should use Class.isAssignableFrom(Class) .

    if (XPathDataElement.class.isAssignableFrom(field.getType())) 

   would be the code.

2. I guess your real question is how to get the value of a field reflectively? If so, then Field.get(Object) is what you want. The object that you pass to get() is the one whose field you want to retrieve; if you're operating on this (which is a strong code smell), then your code would be

    XPathDataElement tmp = (XPathDataElement) field.get(this); 

Answer 2

I strongly suggest avoiding reflection unless you really need it.

Just write the code out:

this.x.doSomething();
this.y.doSomething();
this.z.doSomething();

Or if you like:

for (A a : new A[] {
    this.x, this.y, this.z
}) {
    a.doSomething();
}

Answer 3

A couple of pointers:

1. Compare the classes for equality, not their names.

   field.getType().equals(XPathDataElement.class)

2. Or better yet, use isAssignableFrom(java.lang.Class) to handle the case where the class declares a return type as a sublclass of what you're looking for

   XPathDataElement.class.isAssignableFrom(field.getType())

3. You're iterating over fields , not method . Your question leads me to assume you want the latter, and if so, use:

   this.getClass().getDeclaredMethods()

Answer 4

You don't seem to assign anything to the obj that you cast to XPathDataElement in the loop.

You probably want to do something like this:

tmp = (XPathDataElement)field.get(this);