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Java example source code file (Objects.java)

This example Java source code file (Objects.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.

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Java - Java tags/keywords

annotation, canignorereturnvalue, deprecated, gwtcompatible, nullable, object, objects, override, stringbuilder, tostringhelper, util, valueholder

The Objects.java Java example source code

/*
 * Copyright (C) 2007 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 com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;

import java.util.Arrays;

import javax.annotation.Nullable;

/**
 * Helper functions that can operate on any {@code Object}.
 *
 * <p>See the Guava User Guide on
 * <a href="https://github.com/google/guava/wiki/CommonObjectUtilitiesExplained">writing
 * {@code Object} methods with {@code Objects}</a>.
 *
 * @author Laurence Gonsalves
 * @since 2.0
 */
@GwtCompatible
public final class Objects {
  private Objects() {}

  /**
   * Determines whether two possibly-null objects are equal. Returns:
   *
   * <ul>
   * <li>{@code true} if {@code a} and {@code b} are both null.
   * <li>{@code true} if {@code a} and {@code b} are both non-null and they are equal according to
   *     {@link Object#equals(Object)}.
   * <li>{@code false} in all other situations.
   * </ul>
   *
   * <p>This assumes that any non-null objects passed to this function conform to the
   * {@code equals()} contract.
   *
   * <p>Note for Java 7 and later: This method should be treated as deprecated; use
   * {@link java.util.Objects#equals} instead.
   */
  public static boolean equal(@Nullable Object a, @Nullable Object b) {
    return a == b || (a != null && a.equals(b));
  }

  /**
   * Generates a hash code for multiple values. The hash code is generated by calling
   * {@link Arrays#hashCode(Object[])}. Note that array arguments to this method, with the exception
   * of a single Object array, do not get any special handling; their hash codes are based on
   * identity and not contents.
   *
   * <p>This is useful for implementing {@link Object#hashCode()}. For example, in an object that
   * has three properties, {@code x}, {@code y}, and {@code z}, one could write:
   *
   * <pre>   {@code
   *   public int hashCode() {
   *     return Objects.hashCode(getX(), getY(), getZ());
   *   }}</pre>
   *
   * <p>Warning: When a single object is supplied, the returned hash code does not equal the
   * hash code of that object.
   *
   * <p>Note for Java 7 and later: This method should be treated as deprecated; use
   * {@link java.util.Objects#hash} instead.
   */
  public static int hashCode(@Nullable Object... objects) {
    return Arrays.hashCode(objects);
  }

  /**
   * Creates an instance of {@link ToStringHelper}.
   *
   * <p>This is helpful for implementing {@link Object#toString()}. Specification by example:
   *
   * <pre>   {@code
   *   // Returns "ClassName{}"
   *   Objects.toStringHelper(this)
   *       .toString();
   *
   *   // Returns "ClassName{x=1}"
   *   Objects.toStringHelper(this)
   *       .add("x", 1)
   *       .toString();
   *
   *   // Returns "MyObject{x=1}"
   *   Objects.toStringHelper("MyObject")
   *       .add("x", 1)
   *       .toString();
   *
   *   // Returns "ClassName{x=1, y=foo}"
   *   Objects.toStringHelper(this)
   *       .add("x", 1)
   *       .add("y", "foo")
   *       .toString();
   *
   *   // Returns "ClassName{x=1}"
   *   Objects.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 2.0
   * @deprecated Use {@link MoreObjects#toStringHelper(Object)} instead. This method is scheduled
   *     for removal in August 2016.
   */
  @Deprecated
  public static ToStringHelper toStringHelper(Object self) {
    return new ToStringHelper(self.getClass().getSimpleName());
  }

  /**
   * Creates an instance of {@link ToStringHelper} in the same manner as
   * {@link Objects#toStringHelper(Object)}, but using the 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 7.0 (source-compatible since 2.0)
   * @deprecated Use {@link MoreObjects#toStringHelper(Class)} instead. This method is scheduled for
   *     removal in August 2016.
   */
  @Deprecated
  public static ToStringHelper toStringHelper(Class<?> clazz) {
    return new ToStringHelper(clazz.getSimpleName());
  }

  /**
   * Creates an instance of {@link ToStringHelper} in the same manner as
   * {@link Objects#toStringHelper(Object)}, but using {@code className} instead of using an
   * instance's {@link Object#getClass()}.
   *
   * @param className the name of the instance type
   * @since 7.0 (source-compatible since 2.0)
   * @deprecated Use {@link MoreObjects#toStringHelper(String)} instead. This method is scheduled
   *     for removal in August 2016.
   */
  @Deprecated
  public static ToStringHelper toStringHelper(String className) {
    return new ToStringHelper(className);
  }

  /**
   * Returns the first of two given parameters that is not {@code null}, if either is, or otherwise
   * throws a {@link NullPointerException}.
   *
   * <p>Note: if {@code first} is represented as an {@link Optional}, this can be
   * accomplished with {@linkplain Optional#or(Object) first.or(second)}. That approach also allows
   * for lazy evaluation of the fallback instance, using {@linkplain Optional#or(Supplier)
   * first.or(Supplier)}.
   *
   * @return {@code first} if {@code first} is not {@code null}, or {@code second} if {@code first}
   *     is {@code null} and {@code second} is not {@code null}
   * @throws NullPointerException if both {@code first} and {@code second} were {@code null}
   * @since 3.0
   * @deprecated Use {@link MoreObjects#firstNonNull} instead. This method is scheduled for removal
   *     in August 2016.
   */
  @Deprecated
  public static <T> T firstNonNull(@Nullable T first, @Nullable T second) {
    return MoreObjects.firstNonNull(first, second);
  }

  /**
   * Support class for {@link Objects#toStringHelper}.
   *
   * @author Jason Lee
   * @since 2.0
   * @deprecated Use {@link MoreObjects.ToStringHelper} instead. This class is scheduled for removal
   *     in August 2016.
   */
  @Deprecated
  public static final class ToStringHelper {
    private final String className;
    private final ValueHolder holderHead = new ValueHolder();
    private ValueHolder holderTail = holderHead;
    private boolean omitNullValues = false;

    /**
     * Use {@link Objects#toStringHelper(Object)} to create an instance.
     */
    private ToStringHelper(String className) {
      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 12.0
     */
    @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, @Nullable Object value) {
      return addHolder(name, value);
    }

    /**
     * Adds a name/value pair to the formatted output in {@code name=value} format.
     *
     * @since 11.0 (source-compatible since 2.0)
     */
    @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 11.0 (source-compatible since 2.0)
     */
    @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 11.0 (source-compatible since 2.0)
     */
    @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 11.0 (source-compatible since 2.0)
     */
    @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 11.0 (source-compatible since 2.0)
     */
    @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 11.0 (source-compatible since 2.0)
     */
    @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(@Nullable 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 11.0 (source-compatible since 2.0)
     */
    @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 11.0 (source-compatible since 2.0)
     */
    @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 11.0 (source-compatible since 2.0)
     */
    @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 11.0 (source-compatible since 2.0)
     */
    @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 11.0 (source-compatible since 2.0)
     */
    @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 11.0 (source-compatible since 2.0)
     */
    @CanIgnoreReturnValue
    public ToStringHelper addValue(long value) {
      return addHolder(String.valueOf(value));
    }

    /**
     * Returns a string in the format specified by {@link Objects#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) {
        if (!omitNullValuesSnapshot || valueHolder.value != null) {
          builder.append(nextSeparator);
          nextSeparator = ", ";

          if (valueHolder.name != null) {
            builder.append(valueHolder.name).append('=');
          }
          builder.append(valueHolder.value);
        }
      }
      return builder.append('}').toString();
    }

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

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

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

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

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