filteriteratortest.java

BOOK:Beginning Algorithms Code Examples

package com.wrox.algorithms.iteration;

import junit.framework.TestCase;

/**
 * Test cases for {@link FilterIterator}.
 *
 */
public class FilterIteratorTest extends TestCase {
    private static final Object[] ARRAY = {"A", "B", "C"};

    public void testForwardsIterationIncludesItemsWhenPredicateReturnsTrue() {
        Iterator expectedIterator = new ArrayIterator(ARRAY);
        Iterator underlyingIterator = new ArrayIterator(ARRAY);

        Iterator iterator = new FilterIterator(underlyingIterator, new DummyPredicate(true, expectedIterator));

        iterator.first();
        assertFalse(iterator.isDone());
        assertSame(ARRAY[0], iterator.current());

        iterator.next();
        assertFalse(iterator.isDone());
        assertSame(ARRAY[1], iterator.current());

        iterator.next();
        assertFalse(iterator.isDone());
        assertSame(ARRAY[2], iterator.current());

        iterator.next();
        assertTrue(iterator.isDone());
        try {
            iterator.current();
            fail();
        } catch (IteratorOutOfBoundsException e) {
            // expected
        }

        assertTrue(expectedIterator.isDone());
        assertTrue(underlyingIterator.isDone());
    }

    public void testForwardsIterationExcludesItemsWhenPredicateReturnsFalse() {
        Iterator expectedIterator = new ArrayIterator(ARRAY);
        Iterator underlyingIterator = new ArrayIterator(ARRAY);

        Iterator iterator = new FilterIterator(underlyingIterator, new DummyPredicate(false, expectedIterator));

        iterator.first();
        assertTrue(iterator.isDone());
        try {
            iterator.current();
            fail();
        } catch (IteratorOutOfBoundsException e) {
            // expected
        }

        assertTrue(expectedIterator.isDone());
        assertTrue(underlyingIterator.isDone());
    }

    public void testBackwardssIterationIncludesItemsWhenPredicateReturnsTrue() {
        Iterator expectedIterator = new ReverseIterator(new ArrayIterator(ARRAY));
        Iterator underlyingIterator = new ArrayIterator(ARRAY);

        Iterator iterator = new FilterIterator(underlyingIterator, new DummyPredicate(true, expectedIterator));

        iterator.last();
        assertFalse(iterator.isDone());
        assertSame(ARRAY[2], iterator.current());

        iterator.previous();
        assertFalse(iterator.isDone());
        assertSame(ARRAY[1], iterator.current());

        iterator.previous();
        assertFalse(iterator.isDone());
        assertSame(ARRAY[0], iterator.current());

        iterator.previous();
        assertTrue(iterator.isDone());
        try {
            iterator.current();
            fail();
        } catch (IteratorOutOfBoundsException e) {
            // expected
        }

        assertTrue(expectedIterator.isDone());
        assertTrue(underlyingIterator.isDone());
    }

    public void testBackwardsIterationExcludesItemsWhenPredicateReturnsFalse() {
        Iterator expectedIterator = new ReverseIterator(new ArrayIterator(ARRAY));
        Iterator underlyingIterator = new ArrayIterator(ARRAY);

        Iterator iterator = new FilterIterator(underlyingIterator, new DummyPredicate(false, expectedIterator));

        iterator.last();
        assertTrue(iterator.isDone());
        try {
            iterator.current();
            fail();
        } catch (IteratorOutOfBoundsException e) {
            // expected
        }

        assertTrue(expectedIterator.isDone());
        assertTrue(underlyingIterator.isDone());
    }

    private static final class DummyPredicate implements Predicate {
        private final Iterator _iterator;
        private final boolean _result;

        public DummyPredicate(boolean result, Iterator iterator) {
            _iterator = iterator;
            _result = result;
            _iterator.first();
        }

        public boolean evaluate(Object object) {
            assertSame(_iterator.current(), object);
            _iterator.next();
            return _result;
        }
    }
}