Create new instance from Constructor : Constructor « Reflection « Java Tutorial

1. Java Tutorial
2. Reflection
3. Constructor

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import static java.lang.System.out;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

class EmailAliases {
  private Set<String> aliases;

  private EmailAliases(HashMap<String, String> h) {
    aliases = h.keySet();
  }

  public void printKeys() {
    out.format("Mail keys:%n");
    for (String k : aliases)
      out.format("  %s%n", k);
  }
}

public class RestoreAliases {

  private static Map<String, String> defaultAliases = new HashMap<String, String>();
  static {
    defaultAliases.put("Duke", "duke@i-love-java");
    defaultAliases.put("Fang", "fang@evil-jealous-twin");
  }

  public static void main(String... args) {
    try {
      Constructor ctor = EmailAliases.class.getDeclaredConstructor(HashMap.class);
      ctor.setAccessible(true);
      EmailAliases email = (EmailAliases) ctor.newInstance(defaultAliases);
      email.printKeys();

      // production code should handle these exceptions more gracefully
    } catch (InstantiationException x) {
      x.printStackTrace();
    } catch (IllegalAccessException x) {
      x.printStackTrace();
    } catch (InvocationTargetException x) {
      x.printStackTrace();
    } catch (NoSuchMethodException x) {
      x.printStackTrace();
    }
  }
}