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Java example source code file (Helpers.java)

This example Java source code file (Helpers.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

collection, comparable, comparator, iterable, iterator, list, not, nullsbefore, object, override, reflection, string, util

The Helpers.java Java example source code

/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect.testing;

import static java.util.Collections.sort;
import static junit.framework.Assert.assertEquals;
import static junit.framework.Assert.assertFalse;
import static junit.framework.Assert.assertTrue;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;

import junit.framework.Assert;
import junit.framework.AssertionFailedError;

import java.io.Serializable;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

@GwtCompatible(emulated = true)
public class Helpers {
  // Clone of Objects.equal
  static boolean equal(Object a, Object b) {
    return a == b || (a != null && a.equals(b));
  }

  // Clone of Lists.newArrayList
  public static <E> List copyToList(Iterable elements) {
    List<E> list = new ArrayList();
    addAll(list, elements);
    return list;
  }

  public static <E> List copyToList(E[] elements) {
    return copyToList(Arrays.asList(elements));
  }

  // Clone of Sets.newLinkedHashSet
  public static <E> Set copyToSet(Iterable elements) {
    Set<E> set = new LinkedHashSet();
    addAll(set, elements);
    return set;
  }

  public static <E> Set copyToSet(E[] elements) {
    return copyToSet(Arrays.asList(elements));
  }

  // Would use Maps.immutableEntry
  public static <K, V> Entry mapEntry(K key, V value) {
    return Collections.singletonMap(key, value).entrySet().iterator().next();
  }

  private static boolean isEmpty(Iterable<?> iterable) {
    return iterable instanceof Collection
        ? ((Collection<?>) iterable).isEmpty()
        : iterable.iterator().hasNext();
  }

  public static void assertEmpty(Iterable<?> iterable) {
    if (!isEmpty(iterable)) {
      Assert.fail("Not true that " + iterable + " is empty");
    }
  }

  public static void assertEmpty(Map<?, ?> map) {
    if (!map.isEmpty()) {
      Assert.fail("Not true that " + map + " is empty");
    }
  }

  public static void assertEqualInOrder(Iterable<?> expected, Iterable actual) {
    Iterator<?> expectedIter = expected.iterator();
    Iterator<?> actualIter = actual.iterator();

    while (expectedIter.hasNext() && actualIter.hasNext()) {
      if (!equal(expectedIter.next(), actualIter.next())) {
        Assert.fail(
            "contents were not equal and in the same order: "
                + "expected = "
                + expected
                + ", actual = "
                + actual);
      }
    }

    if (expectedIter.hasNext() || actualIter.hasNext()) {
      // actual either had too few or too many elements
      Assert.fail(
          "contents were not equal and in the same order: "
              + "expected = "
              + expected
              + ", actual = "
              + actual);
    }
  }

  public static void assertContentsInOrder(Iterable<?> actual, Object... expected) {
    assertEqualInOrder(Arrays.asList(expected), actual);
  }

  public static void assertEqualIgnoringOrder(Iterable<?> expected, Iterable actual) {
    List<?> exp = copyToList(expected);
    List<?> act = copyToList(actual);
    String actString = act.toString();

    // Of course we could take pains to give the complete description of the
    // problem on any failure.

    // Yeah it's n^2.
    for (Object object : exp) {
      if (!act.remove(object)) {
        Assert.fail(
            "did not contain expected element "
                + object
                + ", "
                + "expected = "
                + exp
                + ", actual = "
                + actString);
      }
    }
    assertTrue("unexpected elements: " + act, act.isEmpty());
  }

  public static void assertContentsAnyOrder(Iterable<?> actual, Object... expected) {
    assertEqualIgnoringOrder(Arrays.asList(expected), actual);
  }

  public static void assertContains(Iterable<?> actual, Object expected) {
    boolean contained = false;
    if (actual instanceof Collection) {
      contained = ((Collection<?>) actual).contains(expected);
    } else {
      for (Object o : actual) {
        if (equal(o, expected)) {
          contained = true;
          break;
        }
      }
    }

    if (!contained) {
      Assert.fail("Not true that " + actual + " contains " + expected);
    }
  }

  public static void assertContainsAllOf(Iterable<?> actual, Object... expected) {
    List<Object> expectedList = new ArrayList();
    expectedList.addAll(Arrays.asList(expected));

    for (Object o : actual) {
      expectedList.remove(o);
    }

    if (!expectedList.isEmpty()) {
      Assert.fail("Not true that " + actual + " contains all of " + Arrays.asList(expected));
    }
  }

  public static <E> boolean addAll(Collection addTo, Iterable elementsToAdd) {
    boolean modified = false;
    for (E e : elementsToAdd) {
      modified |= addTo.add(e);
    }
    return modified;
  }

  static <T> Iterable reverse(final List list) {
    return new Iterable<T>() {
      @Override
      public Iterator<T> iterator() {
        final ListIterator<T> listIter = list.listIterator(list.size());
        return new Iterator<T>() {
          @Override
          public boolean hasNext() {
            return listIter.hasPrevious();
          }

          @Override
          public T next() {
            return listIter.previous();
          }

          @Override
          public void remove() {
            listIter.remove();
          }
        };
      }
    };
  }

  static <T> Iterator cycle(final Iterable iterable) {
    return new Iterator<T>() {
      Iterator<T> iterator = Collections.emptySet().iterator();

      @Override
      public boolean hasNext() {
        return true;
      }

      @Override
      public T next() {
        if (!iterator.hasNext()) {
          iterator = iterable.iterator();
        }
        return iterator.next();
      }

      @Override
      public void remove() {
        throw new UnsupportedOperationException();
      }
    };
  }

  static <T> T get(Iterator iterator, int position) {
    for (int i = 0; i < position; i++) {
      iterator.next();
    }
    return iterator.next();
  }

  static void fail(Throwable cause, Object message) {
    AssertionFailedError assertionFailedError = new AssertionFailedError(String.valueOf(message));
    assertionFailedError.initCause(cause);
    throw assertionFailedError;
  }

  public static <K, V> Comparator> entryComparator(
      final Comparator<? super K> keyComparator) {
    return new Comparator<Entry() {
      @Override
      @SuppressWarnings("unchecked") // no less safe than putting it in the map!
      public int compare(Entry<K, V> a, Entry b) {
        return (keyComparator == null)
            ? ((Comparable) a.getKey()).compareTo(b.getKey())
            : keyComparator.compare(a.getKey(), b.getKey());
      }
    };
  }

  /**
   * Asserts that all pairs of {@code T} values within {@code valuesInExpectedOrder} are ordered
   * consistently between their order within {@code valuesInExpectedOrder} and the order implied by
   * the given {@code comparator}.
   *
   * @see #testComparator(Comparator, List)
   */
  public static <T> void testComparator(
      Comparator<? super T> comparator, T... valuesInExpectedOrder) {
    testComparator(comparator, Arrays.asList(valuesInExpectedOrder));
  }

  /**
   * Asserts that all pairs of {@code T} values within {@code valuesInExpectedOrder} are ordered
   * consistently between their order within {@code valuesInExpectedOrder} and the order implied by
   * the given {@code comparator}.
   *
   * <p>In detail, this method asserts
   * <ul>
   * <li>reflexivity: {@code comparator.compare(t, t) = 0} for all {@code t} in
   * {@code valuesInExpectedOrder}; and
   * <li>consistency: {@code comparator.compare(ti, tj) < 0} and
   * {@code comparator.compare(tj, ti) > 0} for {@code i < j}, where
   * {@code ti = valuesInExpectedOrder.get(i)} and {@code tj = valuesInExpectedOrder.get(j)}.
   */
  public static <T> void testComparator(
      Comparator<? super T> comparator, List valuesInExpectedOrder) {
    // This does an O(n^2) test of all pairs of values in both orders
    for (int i = 0; i < valuesInExpectedOrder.size(); i++) {
      T t = valuesInExpectedOrder.get(i);

      for (int j = 0; j < i; j++) {
        T lesser = valuesInExpectedOrder.get(j);
        assertTrue(
            comparator + ".compare(" + lesser + ", " + t + ")", comparator.compare(lesser, t) < 0);
      }

      assertEquals(comparator + ".compare(" + t + ", " + t + ")", 0, comparator.compare(t, t));

      for (int j = i + 1; j < valuesInExpectedOrder.size(); j++) {
        T greater = valuesInExpectedOrder.get(j);
        assertTrue(
            comparator + ".compare(" + greater + ", " + t + ")",
            comparator.compare(greater, t) > 0);
      }
    }
  }

  public static <T extends Comparable void testCompareToAndEquals(
      List<T> valuesInExpectedOrder) {
    // This does an O(n^2) test of all pairs of values in both orders
    for (int i = 0; i < valuesInExpectedOrder.size(); i++) {
      T t = valuesInExpectedOrder.get(i);

      for (int j = 0; j < i; j++) {
        T lesser = valuesInExpectedOrder.get(j);
        assertTrue(lesser + ".compareTo(" + t + ')', lesser.compareTo(t) < 0);
        assertFalse(lesser.equals(t));
      }

      assertEquals(t + ".compareTo(" + t + ')', 0, t.compareTo(t));
      assertTrue(t.equals(t));

      for (int j = i + 1; j < valuesInExpectedOrder.size(); j++) {
        T greater = valuesInExpectedOrder.get(j);
        assertTrue(greater + ".compareTo(" + t + ')', greater.compareTo(t) > 0);
        assertFalse(greater.equals(t));
      }
    }
  }

  /**
   * Returns a collection that simulates concurrent modification by
   * having its size method return incorrect values.  This is useful
   * for testing methods that must treat the return value from size()
   * as a hint only.
   *
   * @param delta the difference between the true size of the
   * collection and the values returned by the size method
   */
  public static <T> Collection misleadingSizeCollection(final int delta) {
    // It would be nice to be able to return a real concurrent
    // collection like ConcurrentLinkedQueue, so that e.g. concurrent
    // iteration would work, but that would not be GWT-compatible.
    return new ArrayList<T>() {
      @Override
      public int size() {
        return Math.max(0, super.size() + delta);
      }
    };
  }

  /**
   * Returns a "nefarious" map entry with the specified key and value,
   * meaning an entry that is suitable for testing that map entries cannot be
   * modified via a nefarious implementation of equals. This is used for testing
   * unmodifiable collections of map entries; for example, it should not be
   * possible to access the raw (modifiable) map entry via a nefarious equals
   * method.
   */
  public static <K, V> Map.Entry nefariousMapEntry(final K key, final V value) {
    return new Map.Entry<K, V>() {
      @Override
      public K getKey() {
        return key;
      }

      @Override
      public V getValue() {
        return value;
      }

      @Override
      public V setValue(V value) {
        throw new UnsupportedOperationException();
      }

      @SuppressWarnings("unchecked")
      @Override
      public boolean equals(Object o) {
        if (o instanceof Map.Entry) {
          Map.Entry<K, V> e = (Map.Entry) o;
          e.setValue(value); // muhahaha!

          return equal(this.getKey(), e.getKey()) && equal(this.getValue(), e.getValue());
        }
        return false;
      }

      @Override
      public int hashCode() {
        K k = getKey();
        V v = getValue();
        return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode());
      }

      @Override
      public String toString() {
        return getKey() + "=" + getValue();
      }
    };
  }

  static <E> List castOrCopyToList(Iterable iterable) {
    if (iterable instanceof List) {
      return (List<E>) iterable;
    }
    List<E> list = new ArrayList();
    for (E e : iterable) {
      list.add(e);
    }
    return list;
  }

  private static final Comparator<Comparable> NATURAL_ORDER =
      new Comparator<Comparable>() {
        @SuppressWarnings("unchecked") // assume any Comparable is Comparable<Self>
        @Override
        public int compare(Comparable left, Comparable right) {
          return left.compareTo(right);
        }
      };

  public static <K extends Comparable, V> Iterable> orderEntriesByKey(
      List<Entry insertionOrder) {
    sort(insertionOrder, Helpers.<K, V>entryComparator(NATURAL_ORDER));
    return insertionOrder;
  }

  /**
   * Private replacement for {@link com.google.gwt.user.client.rpc.GwtTransient} to work around
   * build-system quirks.
   */
  private @interface GwtTransient {}

  /**
   * Compares strings in natural order except that null comes immediately before a given value. This
   * works better than Ordering.natural().nullsFirst() because, if null comes before all other
   * values, it lies outside the submap/submultiset ranges we test, and the variety of tests that
   * exercise null handling fail on those subcollections.
   */
  public abstract static class NullsBefore implements Comparator<String>, Serializable {
    /*
     * We don't serialize this class in GWT, so we don't care about whether GWT will serialize this
     * field.
     */
    @GwtTransient private final String justAfterNull;

    protected NullsBefore(String justAfterNull) {
      if (justAfterNull == null) {
        throw new NullPointerException();
      }

      this.justAfterNull = justAfterNull;
    }

    @Override
    public int compare(String lhs, String rhs) {
      if (lhs == rhs) {
        return 0;
      }
      if (lhs == null) {
        // lhs (null) comes just before justAfterNull.
        // If rhs is b, lhs comes first.
        if (rhs.equals(justAfterNull)) {
          return -1;
        }
        return justAfterNull.compareTo(rhs);
      }
      if (rhs == null) {
        // rhs (null) comes just before justAfterNull.
        // If lhs is b, rhs comes first.
        if (lhs.equals(justAfterNull)) {
          return 1;
        }
        return lhs.compareTo(justAfterNull);
      }
      return lhs.compareTo(rhs);
    }

    @Override
    public boolean equals(Object obj) {
      if (obj instanceof NullsBefore) {
        NullsBefore other = (NullsBefore) obj;
        return justAfterNull.equals(other.justAfterNull);
      }
      return false;
    }

    @Override
    public int hashCode() {
      return justAfterNull.hashCode();
    }
  }

  public static final class NullsBeforeB extends NullsBefore {
    public static final NullsBeforeB INSTANCE = new NullsBeforeB();

    private NullsBeforeB() {
      super("b");
    }
  }

  public static final class NullsBeforeTwo extends NullsBefore {
    public static final NullsBeforeTwo INSTANCE = new NullsBeforeTwo();

    private NullsBeforeTwo() {
      super("two"); // from TestStringSortedMapGenerator's sample keys
    }
  }

  @GwtIncompatible // reflection
  public static Method getMethod(Class<?> clazz, String name) {
    try {
      return clazz.getMethod(name);
    } catch (Exception e) {
      throw new IllegalArgumentException(e);
    }
  }
}




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