Java example source code file (EmptyIterator.java)

This example Java source code file (EmptyIterator.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

assertionerror, collection, emptyiterator, enumeration, expected, hashtable, iterator, list, object, string, suppresswarnings, throwable, util

The EmptyIterator.java Java example source code

/*
 * Copyright (c) 2007, 2012, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 * @test
 * @bug 5017904 6356890 8004928
 * @summary Test empty iterators, enumerations, and collections
 */

import static java.util.Collections.*;
import java.util.*;

public class EmptyIterator {

    void test(String[] args) throws Throwable {
        testEmptyCollection(Collections.<Object>emptyList());
        testEmptyCollection(Collections.<Object>emptySet());

        testEmptyMap(Collections.<Object, Object>emptyMap());

        Hashtable<Object, Object> emptyTable = new Hashtable();
        testEmptyEnumeration(emptyTable.keys());
        testEmptyEnumeration(emptyTable.elements());
        testEmptyIterator(emptyTable.keySet().iterator());
        testEmptyIterator(emptyTable.values().iterator());
        testEmptyIterator(emptyTable.entrySet().iterator());

        final Enumeration<EmptyIterator> finalEmptyTyped =
            Collections.emptyEnumeration();
        testEmptyEnumeration(finalEmptyTyped);

        final Enumeration finalEmptyAbstract =
            Collections.emptyEnumeration();
        testEmptyEnumeration(finalEmptyAbstract);

        @SuppressWarnings("unchecked") Iterator<?> x =
            new sun.tools.java.MethodSet()
            .lookupName(sun.tools.java.Identifier.lookup(""));
        testEmptyIterator(x);
    }

    <T> void testEmptyEnumeration(final Enumeration e) {
        check(e == emptyEnumeration());
        check(! e.hasMoreElements());
        THROWS(NoSuchElementException.class,
               new F(){void f(){ e.nextElement(); }});
    }

    <T> void testEmptyIterator(final Iterator it) {
        check(it == emptyIterator());
        check(! it.hasNext());
        THROWS(NoSuchElementException.class,
               new F(){void f(){ it.next(); }});
        THROWS(IllegalStateException.class,
               new F(){void f(){ it.remove(); }});
    }

    void testEmptyMap(Map<Object, Object> m) {
        check(m == emptyMap());
        check(m.entrySet().iterator() ==
              Collections.<Map.EntryemptyIterator());
        check(m.values().iterator() == emptyIterator());
        check(m.keySet().iterator() == emptyIterator());
        equal(m, unmodifiableMap(m));

        testEmptyCollection(m.keySet());
        testEmptyCollection(m.entrySet());
        testEmptyCollection(m.values());
    }

    <E> void testToArray(final Collection c) {
        Object[] a = c.toArray();
        equal(a.length, 0);
        equal(a.getClass().getComponentType(), Object.class);
        THROWS(NullPointerException.class,
               new F(){void f(){ c.toArray((Object[])null); }});

        {
            String[] t = new String[0];
            check(c.toArray(t) == t);
        }

        {
            String[] t = nCopies(10, "").toArray(new String[0]);
            check(c.toArray(t) == t);
            check(t[0] == null);
            for (int i=1; i<t.length; i++)
                check(t[i] == "");
        }
    }

    <E> void testEmptyCollection(final Collection c) {
        testEmptyIterator(c.iterator());

        check(c.iterator() == emptyIterator());
        if (c instanceof List)
            check(((List<?>)c).listIterator() == emptyListIterator());

        testToArray(c);
    }

    //--------------------- Infrastructure ---------------------------
    volatile int passed = 0, failed = 0;
    void pass() {passed++;}
    void fail() {failed++; Thread.dumpStack();}
    void fail(String msg) {System.err.println(msg); fail();}
    void unexpected(Throwable t) {failed++; t.printStackTrace();}
    void check(boolean cond) {if (cond) pass(); else fail();}
    void equal(Object x, Object y) {
        if (x == null ? y == null : x.equals(y)) pass();
        else fail(x + " not equal to " + y);}
    public static void main(String[] args) throws Throwable {
        new EmptyIterator().instanceMain(args);}
    void instanceMain(String[] args) throws Throwable {
        try {test(args);} catch (Throwable t) {unexpected(t);}
        System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
        if (failed > 0) throw new AssertionError("Some tests failed");}
    abstract class F {abstract void f() throws Throwable;}
    void THROWS(Class<? extends Throwable> k, F... fs) {
        for (F f : fs)
            try {f.f(); fail("Expected " + k.getName() + " not thrown");}
            catch (Throwable t) {
                if (k.isAssignableFrom(t.getClass())) pass();
                else unexpected(t);}}
}