java-core-examples/copying/src/broken/ForgotToOverride.java

/** Implements Cloneable but forgets to override clone(), then calls it. Does not compile. */
public class ForgotToOverride {

    static class Foo implements Cloneable {
        int x = 1;
    }

    public static void main(String[] args) {
        Foo foo = new Foo();
        Object copy = foo.clone();
        System.out.println(copy);
    }
}