CloneTestB.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 CloneTestB {


    /**
     * 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(); }

        /**
         * Creates a new Foo, which will result in a new WrappedString
         * instance.  Using super.clone(), you'd just get a reference
         * to the same WrappedString instance.
         *
         * @return the cloned object, or null if failed
         */
        public Object clone() {
            return new Foo(getString());
        }
    }

    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 "mango"
    }
}