CloneTestA.java

/**
* Shows a little about Object.clone()'s behavior.
*
* Object.clone() is a native method, so I couldn't look at the source code.
* I believe what it does is to copy object references. That means that
* if you don't override it, all clones will be pointing to the same
* instances of the contained members.
*/
public class CloneTestA {


    /**
     * Only purpose of this class is to contain
     * a value that can be inspected.
     */
    static class WrappedString implements Cloneable {
        private String s;
        public WrappedString() {}
        public WrappedString(String s) { setS(s); }
        public String getS() { return s; }
        public void setS(String s) { this.s = s; }
    }


    /**
     * This class' purpose is to contain an object that implements
     * Cloneable, but does not override Object.clone()'s behavior.
     *
     * The result here is that
     * both cloned objects will contain a reference to the same
     * WrappedString. This is not always what you want; that's why
     * in addition to implementing Cloneable, you usually would want
     * to override Object.clone()'s behavior.
     */
    static class Foo implements Cloneable {
        private WrappedString wrappedString = new WrappedString();
        public Foo(String s) { setString(s); }
        public String getString() { return wrappedString.getS(); }
        public void setString(String s) { wrappedString.setS(s); }
        public String toString() { return getString(); }

        /**
         * Same behavior as Object.clone(); this is only here to make it public
         *
         * @return the cloned object, or null if failed
         */
        public Object clone() {
            Object newObject = null;
            try {
                newObject = super.clone();
            } catch (CloneNotSupportedException e) {
                e.printStackTrace();
            }

            return newObject;
        }
    }

    public static void main(String [] args) {

        Foo f1 = new Foo("mango");
        Foo f2 = (Foo) f1.clone();

        f1.setString("durian");
        System.out.println(f1); // prints "durian"
        System.out.println(f2); // prints "durian" also
    }
}