001/*
002 * Copyright (C) 2014 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.base;
016
017import static com.google.common.base.Preconditions.checkNotNull;
018
019import com.google.common.annotations.GwtCompatible;
020import com.google.errorprone.annotations.CanIgnoreReturnValue;
021import java.lang.reflect.Array;
022import java.util.Arrays;
023import java.util.Collection;
024import java.util.Map;
025import java.util.OptionalDouble;
026import java.util.OptionalInt;
027import java.util.OptionalLong;
028import javax.annotation.CheckForNull;
029
030/**
031 * Helper functions that operate on any {@code Object}, and are not already provided in {@link
032 * java.util.Objects}.
033 *
034 * <p>See the Guava User Guide on <a
035 * href="https://github.com/google/guava/wiki/CommonObjectUtilitiesExplained">writing {@code Object}
036 * methods with {@code MoreObjects}</a>.
037 *
038 * @author Laurence Gonsalves
039 * @since 18.0 (since 2.0 as {@code Objects})
040 */
041@GwtCompatible
042@ElementTypesAreNonnullByDefault
043public final class MoreObjects {
044  /**
045   * Returns the first of two given parameters that is not {@code null}, if either is, or otherwise
046   * throws a {@link NullPointerException}.
047   *
048   * <p>To find the first non-null element in an iterable, use {@code Iterables.find(iterable,
049   * Predicates.notNull())}. For varargs, use {@code Iterables.find(Arrays.asList(a, b, c, ...),
050   * Predicates.notNull())}, static importing as necessary.
051   *
052   * <p><b>Note:</b> if {@code first} is represented as an {@link Optional}, this can be
053   * accomplished with {@link Optional#or(Object) first.or(second)}. That approach also allows for
054   * lazy evaluation of the fallback instance, using {@link Optional#or(Supplier)
055   * first.or(supplier)}.
056   *
057   * <p><b>Java 9 users:</b> use {@code java.util.Objects.requireNonNullElse(first, second)}
058   * instead.
059   *
060   * @return {@code first} if it is non-null; otherwise {@code second} if it is non-null
061   * @throws NullPointerException if both {@code first} and {@code second} are null
062   * @since 18.0 (since 3.0 as {@code Objects.firstNonNull()}).
063   */
064  public static <T> T firstNonNull(@CheckForNull T first, @CheckForNull T second) {
065    if (first != null) {
066      return first;
067    }
068    if (second != null) {
069      return second;
070    }
071    throw new NullPointerException("Both parameters are null");
072  }
073
074  /**
075   * Creates an instance of {@link ToStringHelper}.
076   *
077   * <p>This is helpful for implementing {@link Object#toString()}. Specification by example:
078   *
079   * <pre>{@code
080   * // Returns "ClassName{}"
081   * MoreObjects.toStringHelper(this)
082   *     .toString();
083   *
084   * // Returns "ClassName{x=1}"
085   * MoreObjects.toStringHelper(this)
086   *     .add("x", 1)
087   *     .toString();
088   *
089   * // Returns "MyObject{x=1}"
090   * MoreObjects.toStringHelper("MyObject")
091   *     .add("x", 1)
092   *     .toString();
093   *
094   * // Returns "ClassName{x=1, y=foo}"
095   * MoreObjects.toStringHelper(this)
096   *     .add("x", 1)
097   *     .add("y", "foo")
098   *     .toString();
099   *
100   * // Returns "ClassName{x=1}"
101   * MoreObjects.toStringHelper(this)
102   *     .omitNullValues()
103   *     .add("x", 1)
104   *     .add("y", null)
105   *     .toString();
106   * }</pre>
107   *
108   * <p>Note that in GWT, class names are often obfuscated.
109   *
110   * @param self the object to generate the string for (typically {@code this}), used only for its
111   *     class name
112   * @since 18.0 (since 2.0 as {@code Objects.toStringHelper()}).
113   */
114  public static ToStringHelper toStringHelper(Object self) {
115    return new ToStringHelper(self.getClass().getSimpleName());
116  }
117
118  /**
119   * Creates an instance of {@link ToStringHelper} in the same manner as {@link
120   * #toStringHelper(Object)}, but using the simple name of {@code clazz} instead of using an
121   * instance's {@link Object#getClass()}.
122   *
123   * <p>Note that in GWT, class names are often obfuscated.
124   *
125   * @param clazz the {@link Class} of the instance
126   * @since 18.0 (since 7.0 as {@code Objects.toStringHelper()}).
127   */
128  public static ToStringHelper toStringHelper(Class<?> clazz) {
129    return new ToStringHelper(clazz.getSimpleName());
130  }
131
132  /**
133   * Creates an instance of {@link ToStringHelper} in the same manner as {@link
134   * #toStringHelper(Object)}, but using {@code className} instead of using an instance's {@link
135   * Object#getClass()}.
136   *
137   * @param className the name of the instance type
138   * @since 18.0 (since 7.0 as {@code Objects.toStringHelper()}).
139   */
140  public static ToStringHelper toStringHelper(String className) {
141    return new ToStringHelper(className);
142  }
143
144  /**
145   * Support class for {@link MoreObjects#toStringHelper}.
146   *
147   * @author Jason Lee
148   * @since 18.0 (since 2.0 as {@code Objects.ToStringHelper}).
149   */
150  public static final class ToStringHelper {
151    private final String className;
152    private final ValueHolder holderHead = new ValueHolder();
153    private ValueHolder holderTail = holderHead;
154    private boolean omitNullValues = false;
155    private boolean omitEmptyValues = false;
156
157    /** Use {@link MoreObjects#toStringHelper(Object)} to create an instance. */
158    private ToStringHelper(String className) {
159      this.className = checkNotNull(className);
160    }
161
162    /**
163     * Configures the {@link ToStringHelper} so {@link #toString()} will ignore properties with null
164     * value. The order of calling this method, relative to the {@code add()}/{@code addValue()}
165     * methods, is not significant.
166     *
167     * @since 18.0 (since 12.0 as {@code Objects.ToStringHelper.omitNullValues()}).
168     */
169    @CanIgnoreReturnValue
170    public ToStringHelper omitNullValues() {
171      omitNullValues = true;
172      return this;
173    }
174
175    /**
176     * Adds a name/value pair to the formatted output in {@code name=value} format. If {@code value}
177     * is {@code null}, the string {@code "null"} is used, unless {@link #omitNullValues()} is
178     * called, in which case this name/value pair will not be added.
179     */
180    @CanIgnoreReturnValue
181    public ToStringHelper add(String name, @CheckForNull Object value) {
182      return addHolder(name, value);
183    }
184
185    /**
186     * Adds a name/value pair to the formatted output in {@code name=value} format.
187     *
188     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
189     */
190    @CanIgnoreReturnValue
191    public ToStringHelper add(String name, boolean value) {
192      return addUnconditionalHolder(name, String.valueOf(value));
193    }
194
195    /**
196     * Adds a name/value pair to the formatted output in {@code name=value} format.
197     *
198     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
199     */
200    @CanIgnoreReturnValue
201    public ToStringHelper add(String name, char value) {
202      return addUnconditionalHolder(name, String.valueOf(value));
203    }
204
205    /**
206     * Adds a name/value pair to the formatted output in {@code name=value} format.
207     *
208     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
209     */
210    @CanIgnoreReturnValue
211    public ToStringHelper add(String name, double value) {
212      return addUnconditionalHolder(name, String.valueOf(value));
213    }
214
215    /**
216     * Adds a name/value pair to the formatted output in {@code name=value} format.
217     *
218     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
219     */
220    @CanIgnoreReturnValue
221    public ToStringHelper add(String name, float value) {
222      return addUnconditionalHolder(name, String.valueOf(value));
223    }
224
225    /**
226     * Adds a name/value pair to the formatted output in {@code name=value} format.
227     *
228     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
229     */
230    @CanIgnoreReturnValue
231    public ToStringHelper add(String name, int value) {
232      return addUnconditionalHolder(name, String.valueOf(value));
233    }
234
235    /**
236     * Adds a name/value pair to the formatted output in {@code name=value} format.
237     *
238     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
239     */
240    @CanIgnoreReturnValue
241    public ToStringHelper add(String name, long value) {
242      return addUnconditionalHolder(name, String.valueOf(value));
243    }
244
245    /**
246     * Adds an unnamed value to the formatted output.
247     *
248     * <p>It is strongly encouraged to use {@link #add(String, Object)} instead and give value a
249     * readable name.
250     */
251    @CanIgnoreReturnValue
252    public ToStringHelper addValue(@CheckForNull Object value) {
253      return addHolder(value);
254    }
255
256    /**
257     * Adds an unnamed value to the formatted output.
258     *
259     * <p>It is strongly encouraged to use {@link #add(String, boolean)} instead and give value a
260     * readable name.
261     *
262     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
263     */
264    @CanIgnoreReturnValue
265    public ToStringHelper addValue(boolean value) {
266      return addUnconditionalHolder(String.valueOf(value));
267    }
268
269    /**
270     * Adds an unnamed value to the formatted output.
271     *
272     * <p>It is strongly encouraged to use {@link #add(String, char)} instead and give value a
273     * readable name.
274     *
275     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
276     */
277    @CanIgnoreReturnValue
278    public ToStringHelper addValue(char value) {
279      return addUnconditionalHolder(String.valueOf(value));
280    }
281
282    /**
283     * Adds an unnamed value to the formatted output.
284     *
285     * <p>It is strongly encouraged to use {@link #add(String, double)} instead and give value a
286     * readable name.
287     *
288     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
289     */
290    @CanIgnoreReturnValue
291    public ToStringHelper addValue(double value) {
292      return addUnconditionalHolder(String.valueOf(value));
293    }
294
295    /**
296     * Adds an unnamed value to the formatted output.
297     *
298     * <p>It is strongly encouraged to use {@link #add(String, float)} instead and give value a
299     * readable name.
300     *
301     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
302     */
303    @CanIgnoreReturnValue
304    public ToStringHelper addValue(float value) {
305      return addUnconditionalHolder(String.valueOf(value));
306    }
307
308    /**
309     * Adds an unnamed value to the formatted output.
310     *
311     * <p>It is strongly encouraged to use {@link #add(String, int)} instead and give value a
312     * readable name.
313     *
314     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
315     */
316    @CanIgnoreReturnValue
317    public ToStringHelper addValue(int value) {
318      return addUnconditionalHolder(String.valueOf(value));
319    }
320
321    /**
322     * Adds an unnamed value to the formatted output.
323     *
324     * <p>It is strongly encouraged to use {@link #add(String, long)} instead and give value a
325     * readable name.
326     *
327     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
328     */
329    @CanIgnoreReturnValue
330    public ToStringHelper addValue(long value) {
331      return addUnconditionalHolder(String.valueOf(value));
332    }
333
334    private static boolean isEmpty(Object value) {
335      // Put types estimated to be the most frequent first.
336      if (value instanceof CharSequence) {
337        return ((CharSequence) value).length() == 0;
338      } else if (value instanceof Collection) {
339        return ((Collection<?>) value).isEmpty();
340      } else if (value instanceof Map) {
341        return ((Map<?, ?>) value).isEmpty();
342      } else if (value instanceof java.util.Optional) {
343        return !((java.util.Optional<?>) value).isPresent();
344      } else if (value instanceof OptionalInt) {
345        return !((OptionalInt) value).isPresent();
346      } else if (value instanceof OptionalLong) {
347        return !((OptionalLong) value).isPresent();
348      } else if (value instanceof OptionalDouble) {
349        return !((OptionalDouble) value).isPresent();
350      } else if (value instanceof Optional) {
351        return !((Optional) value).isPresent();
352      } else if (value.getClass().isArray()) {
353        return Array.getLength(value) == 0;
354      }
355      return false;
356    }
357
358    /**
359     * Returns a string in the format specified by {@link MoreObjects#toStringHelper(Object)}.
360     *
361     * <p>After calling this method, you can keep adding more properties to later call toString()
362     * again and get a more complete representation of the same object; but properties cannot be
363     * removed, so this only allows limited reuse of the helper instance. The helper allows
364     * duplication of properties (multiple name/value pairs with the same name can be added).
365     */
366    @Override
367    public String toString() {
368      // create a copy to keep it consistent in case value changes
369      boolean omitNullValuesSnapshot = omitNullValues;
370      boolean omitEmptyValuesSnapshot = omitEmptyValues;
371      String nextSeparator = "";
372      StringBuilder builder = new StringBuilder(32).append(className).append('{');
373      for (ValueHolder valueHolder = holderHead.next;
374          valueHolder != null;
375          valueHolder = valueHolder.next) {
376        Object value = valueHolder.value;
377        if (valueHolder instanceof UnconditionalValueHolder
378            || (value == null
379                ? !omitNullValuesSnapshot
380                : (!omitEmptyValuesSnapshot || !isEmpty(value)))) {
381          builder.append(nextSeparator);
382          nextSeparator = ", ";
383
384          if (valueHolder.name != null) {
385            builder.append(valueHolder.name).append('=');
386          }
387          if (value != null && value.getClass().isArray()) {
388            Object[] objectArray = {value};
389            String arrayString = Arrays.deepToString(objectArray);
390            builder.append(arrayString, 1, arrayString.length() - 1);
391          } else {
392            builder.append(value);
393          }
394        }
395      }
396      return builder.append('}').toString();
397    }
398
399    private ValueHolder addHolder() {
400      ValueHolder valueHolder = new ValueHolder();
401      holderTail = holderTail.next = valueHolder;
402      return valueHolder;
403    }
404
405    @CanIgnoreReturnValue
406    private ToStringHelper addHolder(@CheckForNull Object value) {
407      ValueHolder valueHolder = addHolder();
408      valueHolder.value = value;
409      return this;
410    }
411
412    @CanIgnoreReturnValue
413    private ToStringHelper addHolder(String name, @CheckForNull Object value) {
414      ValueHolder valueHolder = addHolder();
415      valueHolder.value = value;
416      valueHolder.name = checkNotNull(name);
417      return this;
418    }
419
420    private UnconditionalValueHolder addUnconditionalHolder() {
421      UnconditionalValueHolder valueHolder = new UnconditionalValueHolder();
422      holderTail = holderTail.next = valueHolder;
423      return valueHolder;
424    }
425
426    @CanIgnoreReturnValue
427    private ToStringHelper addUnconditionalHolder(Object value) {
428      UnconditionalValueHolder valueHolder = addUnconditionalHolder();
429      valueHolder.value = value;
430      return this;
431    }
432
433    @CanIgnoreReturnValue
434    private ToStringHelper addUnconditionalHolder(String name, Object value) {
435      UnconditionalValueHolder valueHolder = addUnconditionalHolder();
436      valueHolder.value = value;
437      valueHolder.name = checkNotNull(name);
438      return this;
439    }
440
441    // Holder object for values that might be null and/or empty.
442    static class ValueHolder {
443      @CheckForNull String name;
444      @CheckForNull Object value;
445      @CheckForNull ValueHolder next;
446    }
447
448    /**
449     * Holder object for values that cannot be null or empty (will be printed unconditionally). This
450     * helps to shortcut most calls to isEmpty(), which is important because the check for emptiness
451     * is relatively expensive. Use a subtype so this also doesn't need any extra storage.
452     */
453    private static final class UnconditionalValueHolder extends ValueHolder {}
454  }
455
456  private MoreObjects() {}
457}