checkcloneable.java

think in java TIJ-3rd-edition-code.zip

//: appendixa:CheckCloneable.java
// Checking to see if a reference can be cloned.
import com.bruceeckel.simpletest.*;

// Can't clone this because it doesn't
// override clone():
class Ordinary {}

// Overrides clone, but doesn't implement
// Cloneable:
class WrongClone extends Ordinary {
  public Object clone()
      throws CloneNotSupportedException {
    return super.clone(); // Throws exception
  }
}

// Does all the right things for cloning:
class IsCloneable extends Ordinary 
implements Cloneable {
  public Object clone() 
      throws CloneNotSupportedException {
    return super.clone();
  }
}

// Turn off cloning by throwing the exception:
class NoMore extends IsCloneable {
  public Object clone() 
      throws CloneNotSupportedException {
    throw new CloneNotSupportedException();
  }
}

class TryMore extends NoMore {
  public Object clone() 
      throws CloneNotSupportedException {
    // Calls NoMore.clone(), throws exception:
    return super.clone();
  }
}

class BackOn extends NoMore {
  private BackOn duplicate(BackOn b) {
    // Somehow make a copy of b
    // and return that copy. This is a dummy
    // copy, just to make the point:
    return new BackOn();
  }
  public Object clone() {
    // Doesn't call NoMore.clone():
    return duplicate(this);
  }
}

// Can't inherit from this, so can't override
// the clone method like in BackOn:
final class ReallyNoMore extends NoMore {}

public class CheckCloneable {
  static Ordinary tryToClone(Ordinary ord) {
    String id = ord.getClass().getName();
    System.out.println("Attempting " + id);
    Ordinary x = null;
    if(ord instanceof Cloneable) {
      try {
        x = (Ordinary)((IsCloneable)ord).clone();
        System.out.println("Cloned " + id);
      } catch(CloneNotSupportedException e) {
        System.err.println("Could not clone "+id);
      }
    } else {
      System.out.println(
        "Not instance of Cloneable");
    }
    return x;
  }
  public static void main(String[] args) {
    SimpleTest monitor =
      new SimpleTest("CheckCloneable");
    // Upcasting:
    Ordinary[] ord = { 
      new IsCloneable(),
      new WrongClone(),
      new NoMore(),
      new TryMore(),
      new BackOn(),
      new ReallyNoMore(),
    };
    Ordinary x = new Ordinary();
    // This won't compile, since clone() is
    // protected in Object:
    //! x = (Ordinary)x.clone();
    // tryToClone() checks first to see if
    // a class implements Cloneable:
    for(int i = 0; i < ord.length; i++)
      tryToClone(ord[i]);
    monitor.expect(new String[] {
      "Attempting IsCloneable",
      "Cloned IsCloneable",
      "Attempting WrongClone",
      "Not instance of Cloneable",
      "Attempting NoMore",
      "Could not clone NoMore",
      "Attempting TryMore",
      "Could not clone TryMore",
      "Attempting BackOn",
      "Cloned BackOn",
      "Attempting ReallyNoMore",
      "Could not clone ReallyNoMore"
    });
  }
} ///:~