listing28.2.java

来自「java 完全探索的随书源码」· Java 代码 · 共 79 行

/*
 * Requestor
 */
import java.lang.reflect.*;
public class Requestor {

  // Return an array of Provider instances that
  // includes an instance created with each
  // constructor declared by the class
  public static Provider[] constructProvider() {

    Provider[] prov = null;
    try {
      // load the class and retrieve its constructors
      Class cl = Class.forName("Provider");
      Constructor[] con = cl.getDeclaredConstructors();

      // allocate the Provider array based on the
      // number of constructors found
      prov = new Provider[con.length];
      for (int i=0; i<con.length; i++) {
        // get parameter info for the constructor
        Class param[] = con[i].getParameterTypes();
        // create an array to hold the number of
        // parameters required by this constructor
        Object paramValues[] = new Object[param.length];
        // look at each parameter type
        for (int x=0; x<param.length; x++) {
          if (!param[x].isPrimitive()) {
            System.out.println("param:" + param[x]);
            // create an object of this parameter type
            // using its no-argument constructor
            paramValues[x] = param[x].newInstance();
          }
        }
        // the parameter array has been loaded, so create
        // an object using this Provider constructor
        prov[i] = (Provider)con[i].newInstance(paramValues);
      }
    }
    catch (InvocationTargetException e) {
      System.out.println("Could not get class info");
    }
    catch (Exception e) {
      System.out.println("Exception during construction");
    }
    // return the array of Providers
    return prov;
  }

  public static void main(String args[]) {
    // create a Provider instance from each constructor
    Provider[] prov = Requestor.constructProvider();
    for (int i=0; i<prov.length; i++) {
      // display the Provider's one attribute to see which
      // constructor it was created by
      System.out.println("Created provider with attribute: " +
        prov[i].attribute);
    }
  }
}

/*
 * Provider
 *   A simple class with one field and two constructors
 */
class Provider{
    String attribute;
    // Declare a no-argument constructor
    public Provider(){
        attribute = "Not specified";
    }

    // Declare a single-argument constructor
    public Provider(String s){
        attribute = s;
    }
}