Maps.java

package org.robobinding.util;

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;

/**
 * Migrated from {@link com.google.common.collect.Maps}
 * @since 1.0
 * @author Cheng Wei
 *
 */
public class Maps {
  /**
   * Creates a <i>mutable</i>, empty {@code HashMap} instance.
   *
   * <p><b>Note:</b> if {@code K} is an {@code enum} type, use {@link
   * #newEnumMap} instead.
   *
   * <p><b>Note for Java 7 and later:</b> this method is now unnecessary and
   * should be treated as deprecated. Instead, use the {@code HashMap}
   * constructor directly, taking advantage of the new
   * <a href="http://goo.gl/iz2Wi">"diamond" syntax</a>.
   *
   * @return a new, empty {@code HashMap}
   */
  public static <K, V> HashMap<K, V> newHashMap() {
    return new HashMap<K, V>();
  }
  /**
   * Creates a <i>mutable</i>, empty, insertion-ordered {@code LinkedHashMap}
   * instance.
   *
   * <p><b>Note for Java 7 and later:</b> this method is now unnecessary and
   * should be treated as deprecated. Instead, use the {@code LinkedHashMap}
   * constructor directly, taking advantage of the new
   * <a href="http://goo.gl/iz2Wi">"diamond" syntax</a>.
   *
   * @return a new, empty {@code LinkedHashMap}
   */
  public static <K, V> LinkedHashMap<K, V> newLinkedHashMap() {
    return new LinkedHashMap<K, V>();
  }
  /**
   * Returns a capacity that is sufficient to keep the map from being resized as
   * long as it grows no larger than expectedSize and the load factor is >= its
   * default (0.75).
   */
  static int capacity(int expectedSize) {
    if (expectedSize < 3) {
      CollectPreconditions.checkNonnegative(expectedSize, "expectedSize");
      return expectedSize + 1;
    }
    if (expectedSize < Ints.MAX_POWER_OF_TWO) {
      // This is the calculation used in JDK8 to resize when a putAll
      // happens; it seems to be the most conservative calculation we
      // can make.  0.75 is the default load factor.
      return (int) ((float) expectedSize / 0.75F + 1.0F);
    }
    return Integer.MAX_VALUE; // any large value
  }

  /**
   * Creates a <i>mutable</i> {@code HashMap} instance with the same mappings as
   * the specified map.
   *
   * <p><b>Note:</b> if mutability is not required, use 
   * ImmutableMap#copyOf(Map) instead.
   *
   * <p><b>Note:</b> if {@code K} is an {@link Enum} type, use {@link
   * #newEnumMap} instead.
   *
   * <p><b>Note for Java 7 and later:</b> this method is now unnecessary and
   * should be treated as deprecated. Instead, use the {@code HashMap}
   * constructor directly, taking advantage of the new
   * <a href="http://goo.gl/iz2Wi">"diamond" syntax</a>.
   *
   * @param map the mappings to be placed in the new map
   * @return a new {@code HashMap} initialized with the mappings from {@code
   *         map}
   */
  public static <K, V> HashMap<K, V> newHashMap(Map<? extends K, ? extends V> map) {
    return new HashMap<K, V>(map);
  }

}