MoreObjects.java

/*
 * Copyright (C) 2014 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.base;

import static com.google.common.base.Preconditions.checkNotNull;
import static java.util.logging.Level.WARNING;

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.concurrent.GuardedBy;
import java.util.Arrays;
import java.util.logging.Logger;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;

/**
 * Helper functions that operate on any {@code Object}, and are not already provided in {@link
 * java.util.Objects}.
 *
 * <p>See the Guava User Guide on <a
 * href="https://github.com/google/guava/wiki/CommonObjectUtilitiesExplained">writing {@code Object}
 * methods with {@code MoreObjects}</a>.
 *
 * @author Laurence Gonsalves
 * @since 18.0 (since 2.0 as {@code Objects})
 */
@GwtCompatible
public final class MoreObjects {
  /**
   * Returns the first of two given parameters that is not {@code null}, if either is, or otherwise
   * throws a {@link NullPointerException}.
   *
   * <p>To find the first non-null element in an iterable, use {@code Iterables.find(iterable,
   * Predicates.notNull())}. For varargs, use {@code Iterables.find(Arrays.asList(a, b, c, ...),
   * Predicates.notNull())}, static importing as necessary.
   *
   * <p><b>Note:</b> if {@code first} is represented as an {@link Optional}, this can be
   * accomplished with {@link Optional#or(Object) first.or(second)}. That approach also allows for
   * lazy evaluation of the fallback instance, using {@link Optional#or(Supplier)
   * first.or(supplier)}.
   *
   * <p><b>Java 9 users:</b> use {@code java.util.Objects.requireNonNullElse(first, second)}
   * instead.
   *
   * @return {@code first} if it is non-null; otherwise {@code second} if it is non-null
   * @throws NullPointerException if both {@code first} and {@code second} are null
   * @since 18.0 (since 3.0 as {@code Objects.firstNonNull()}).
   */
  public static <T> T firstNonNull(@NullableDecl T first, @NullableDecl T second) {
    if (first != null) {
      return first;
    }
    if (second != null) {
      return second;
    }
    throw new NullPointerException("Both parameters are null");
  }

  /**
   * Creates an instance of {@link ToStringHelper}.
   *
   * <p>This is helpful for implementing {@link Object#toString()}. Specification by example:
   *
   * <pre>{@code
   * // Returns "ClassName{}"
   * MoreObjects.toStringHelper(this)
   *     .toString();
   *
   * // Returns "ClassName{x=1}"
   * MoreObjects.toStringHelper(this)
   *     .add("x", 1)
   *     .toString();
   *
   * // Returns "MyObject{x=1}"
   * MoreObjects.toStringHelper("MyObject")
   *     .add("x", 1)
   *     .toString();
   *
   * // Returns "ClassName{x=1, y=foo}"
   * MoreObjects.toStringHelper(this)
   *     .add("x", 1)
   *     .add("y", "foo")
   *     .toString();
   *
   * // Returns "ClassName{x=1}"
   * MoreObjects.toStringHelper(this)
   *     .omitNullValues()
   *     .add("x", 1)
   *     .add("y", null)
   *     .toString();
   * }</pre>
   *
   * <p>Note that in GWT, class names are often obfuscated.
   *
   * @param self the object to generate the string for (typically {@code this}), used only for its
   *     class name
   * @since 18.0 (since 2.0 as {@code Objects.toStringHelper()}).
   */
  public static ToStringHelper toStringHelper(Object self) {
    return new ToStringHelper(self.getClass().getSimpleName());
  }

  /**
   * Creates an instance of {@link ToStringHelper} in the same manner as {@link
   * #toStringHelper(Object)}, but using the simple name of {@code clazz} instead of using an
   * instance's {@link Object#getClass()}.
   *
   * <p>Note that in GWT, class names are often obfuscated.
   *
   * @param clazz the {@link Class} of the instance
   * @since 18.0 (since 7.0 as {@code Objects.toStringHelper()}).
   */
  public static ToStringHelper toStringHelper(Class<?> clazz) {
    return new ToStringHelper(clazz.getSimpleName());
  }

  /**
   * Creates an instance of {@link ToStringHelper} in the same manner as {@link
   * #toStringHelper(Object)}, but using {@code className} instead of using an instance's {@link
   * Object#getClass()}.
   *
   * @param className the name of the instance type
   * @since 18.0 (since 7.0 as {@code Objects.toStringHelper()}).
   */
  public static ToStringHelper toStringHelper(String className) {
    return new ToStringHelper(className);
  }

  /**
   * Support class for {@link MoreObjects#toStringHelper}.
   *
   * @author Jason Lee
   * @since 18.0 (since 2.0 as {@code Objects.ToStringHelper}).
   */
  public static final class ToStringHelper {
    @GuardedBy("ToStringHelper.class")
    private static boolean performedJava8CompatibilityCheck;

    private static void java8CompatibilityCheck() {
      @SuppressWarnings("GuardedBy")
      boolean racyReadForDoubleCheckedLock = performedJava8CompatibilityCheck;
      if (racyReadForDoubleCheckedLock) {
        return;
      }
      synchronized (ToStringHelper.class) {
        if (performedJava8CompatibilityCheck) {
          return;
        }
        performedJava8CompatibilityCheck = true;
      }

      try {
        Java8Usage.performCheck();
      } catch (Throwable underlying) {
        Exception toLog =
            new Exception(
                "Guava will drop support for Java 7 in 2021. Please let us know if this will cause"
                    + " you problems: https://github.com/google/guava/issues/5269",
                underlying);
        Logger.getLogger(ToStringHelper.class.getName())
            .log(
                WARNING,
                "Java 7 compatibility warning: See https://github.com/google/guava/issues/5269",
                toLog);
      }
    }

    private final String className;
    private final ValueHolder holderHead = new ValueHolder();
    private ValueHolder holderTail = holderHead;
    private boolean omitNullValues = false;

    /** Use {@link MoreObjects#toStringHelper(Object)} to create an instance. */
    private ToStringHelper(String className) {
      java8CompatibilityCheck();
      this.className = checkNotNull(className);
    }

    /**
     * Configures the {@link ToStringHelper} so {@link #toString()} will ignore properties with null
     * value. The order of calling this method, relative to the {@code add()}/{@code addValue()}
     * methods, is not significant.
     *
     * @since 18.0 (since 12.0 as {@code Objects.ToStringHelper.omitNullValues()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper omitNullValues() {
      omitNullValues = true;
      return this;
    }

    /**
     * Adds a name/value pair to the formatted output in {@code name=value} format. If {@code value}
     * is {@code null}, the string {@code "null"} is used, unless {@link #omitNullValues()} is
     * called, in which case this name/value pair will not be added.
     */
    @CanIgnoreReturnValue
    public ToStringHelper add(String name, @NullableDecl Object value) {
      return addHolder(name, value);
    }

    /**
     * Adds a name/value pair to the formatted output in {@code name=value} format.
     *
     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper add(String name, boolean value) {
      return addHolder(name, String.valueOf(value));
    }

    /**
     * Adds a name/value pair to the formatted output in {@code name=value} format.
     *
     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper add(String name, char value) {
      return addHolder(name, String.valueOf(value));
    }

    /**
     * Adds a name/value pair to the formatted output in {@code name=value} format.
     *
     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper add(String name, double value) {
      return addHolder(name, String.valueOf(value));
    }

    /**
     * Adds a name/value pair to the formatted output in {@code name=value} format.
     *
     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper add(String name, float value) {
      return addHolder(name, String.valueOf(value));
    }

    /**
     * Adds a name/value pair to the formatted output in {@code name=value} format.
     *
     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper add(String name, int value) {
      return addHolder(name, String.valueOf(value));
    }

    /**
     * Adds a name/value pair to the formatted output in {@code name=value} format.
     *
     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.add()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper add(String name, long value) {
      return addHolder(name, String.valueOf(value));
    }

    /**
     * Adds an unnamed value to the formatted output.
     *
     * <p>It is strongly encouraged to use {@link #add(String, Object)} instead and give value a
     * readable name.
     */
    @CanIgnoreReturnValue
    public ToStringHelper addValue(@NullableDecl Object value) {
      return addHolder(value);
    }

    /**
     * Adds an unnamed value to the formatted output.
     *
     * <p>It is strongly encouraged to use {@link #add(String, boolean)} instead and give value a
     * readable name.
     *
     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper addValue(boolean value) {
      return addHolder(String.valueOf(value));
    }

    /**
     * Adds an unnamed value to the formatted output.
     *
     * <p>It is strongly encouraged to use {@link #add(String, char)} instead and give value a
     * readable name.
     *
     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper addValue(char value) {
      return addHolder(String.valueOf(value));
    }

    /**
     * Adds an unnamed value to the formatted output.
     *
     * <p>It is strongly encouraged to use {@link #add(String, double)} instead and give value a
     * readable name.
     *
     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper addValue(double value) {
      return addHolder(String.valueOf(value));
    }

    /**
     * Adds an unnamed value to the formatted output.
     *
     * <p>It is strongly encouraged to use {@link #add(String, float)} instead and give value a
     * readable name.
     *
     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper addValue(float value) {
      return addHolder(String.valueOf(value));
    }

    /**
     * Adds an unnamed value to the formatted output.
     *
     * <p>It is strongly encouraged to use {@link #add(String, int)} instead and give value a
     * readable name.
     *
     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper addValue(int value) {
      return addHolder(String.valueOf(value));
    }

    /**
     * Adds an unnamed value to the formatted output.
     *
     * <p>It is strongly encouraged to use {@link #add(String, long)} instead and give value a
     * readable name.
     *
     * @since 18.0 (since 11.0 as {@code Objects.ToStringHelper.addValue()}).
     */
    @CanIgnoreReturnValue
    public ToStringHelper addValue(long value) {
      return addHolder(String.valueOf(value));
    }

    /**
     * Returns a string in the format specified by {@link MoreObjects#toStringHelper(Object)}.
     *
     * <p>After calling this method, you can keep adding more properties to later call toString()
     * again and get a more complete representation of the same object; but properties cannot be
     * removed, so this only allows limited reuse of the helper instance. The helper allows
     * duplication of properties (multiple name/value pairs with the same name can be added).
     */
    @Override
    public String toString() {
      // create a copy to keep it consistent in case value changes
      boolean omitNullValuesSnapshot = omitNullValues;
      String nextSeparator = "";
      StringBuilder builder = new StringBuilder(32).append(className).append('{');
      for (ValueHolder valueHolder = holderHead.next;
          valueHolder != null;
          valueHolder = valueHolder.next) {
        Object value = valueHolder.value;
        if (!omitNullValuesSnapshot || value != null) {
          builder.append(nextSeparator);
          nextSeparator = ", ";

          if (valueHolder.name != null) {
            builder.append(valueHolder.name).append('=');
          }
          if (value != null && value.getClass().isArray()) {
            Object[] objectArray = {value};
            String arrayString = Arrays.deepToString(objectArray);
            builder.append(arrayString, 1, arrayString.length() - 1);
          } else {
            builder.append(value);
          }
        }
      }
      return builder.append('}').toString();
    }

    private ValueHolder addHolder() {
      ValueHolder valueHolder = new ValueHolder();
      holderTail = holderTail.next = valueHolder;
      return valueHolder;
    }

    private ToStringHelper addHolder(@NullableDecl Object value) {
      ValueHolder valueHolder = addHolder();
      valueHolder.value = value;
      return this;
    }

    private ToStringHelper addHolder(String name, @NullableDecl Object value) {
      ValueHolder valueHolder = addHolder();
      valueHolder.value = value;
      valueHolder.name = checkNotNull(name);
      return this;
    }

    private static final class ValueHolder {
      @NullableDecl String name;
      @NullableDecl Object value;
      @NullableDecl ValueHolder next;
    }
  }

  private MoreObjects() {}
}