Primitives.java

/*
 * 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.primitives;

import static com.google.common.base.Preconditions.checkNotNull;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/**
 * Contains static utility methods pertaining to primitive types and their
 * corresponding wrapper types.
 *
 * @author Kevin Bourrillion
 * @since 1.0
 */
public final class Primitives {
  private Primitives() {}

  /** A map from primitive types to their corresponding wrapper types. */
  private static final Map<Class<?>, Class<?>> PRIMITIVE_TO_WRAPPER_TYPE;

  /** A map from wrapper types to their corresponding primitive types. */
  private static final Map<Class<?>, Class<?>> WRAPPER_TO_PRIMITIVE_TYPE;

  // Sad that we can't use a BiMap. :(
  
  static {
    Map<Class<?>, Class<?>> primToWrap = new HashMap<Class<?>, Class<?>>(16);
    Map<Class<?>, Class<?>> wrapToPrim = new HashMap<Class<?>, Class<?>>(16);

    add(primToWrap, wrapToPrim, boolean.class, Boolean.class);
    add(primToWrap, wrapToPrim, byte.class, Byte.class);
    add(primToWrap, wrapToPrim, char.class, Character.class);
    add(primToWrap, wrapToPrim, double.class, Double.class);
    add(primToWrap, wrapToPrim, float.class, Float.class);
    add(primToWrap, wrapToPrim, int.class, Integer.class);
    add(primToWrap, wrapToPrim, long.class, Long.class);
    add(primToWrap, wrapToPrim, short.class, Short.class);
    add(primToWrap, wrapToPrim, void.class, Void.class);

    PRIMITIVE_TO_WRAPPER_TYPE = Collections.unmodifiableMap(primToWrap);
    WRAPPER_TO_PRIMITIVE_TYPE = Collections.unmodifiableMap(wrapToPrim);
  }

  private static void add(Map<Class<?>, Class<?>> forward,
      Map<Class<?>, Class<?>> backward, Class<?> key, Class<?> value) {
    forward.put(key, value);
    backward.put(value, key);
  }

  /**
   * Returns an immutable set of all nine primitive types (including {@code
   * void}). Note that a simpler way to test whether a {@code Class} instance
   * is a member of this set is to call {@link Class#isPrimitive}.
   *
   * @since 3.0
   */
  public static Set<Class<?>> allPrimitiveTypes() {
    return PRIMITIVE_TO_WRAPPER_TYPE.keySet();
  }

  /**
   * Returns an immutable set of all nine primitive-wrapper types (including
   * {@link Void}).
   *
   * @since 3.0
   */
  public static Set<Class<?>> allWrapperTypes() {
    return WRAPPER_TO_PRIMITIVE_TYPE.keySet();
  }

  /**
   * Returns {@code true} if {@code type} is one of the nine
   * primitive-wrapper types, such as {@link Integer}.
   *
   * @see Class#isPrimitive
   */
  public static boolean isWrapperType(Class<?> type) {
    return WRAPPER_TO_PRIMITIVE_TYPE.containsKey(checkNotNull(type));
  }

  /**
   * Returns the corresponding wrapper type of {@code type} if it is a primitive
   * type; otherwise returns {@code type} itself. Idempotent.
   * <pre>
   *     wrap(int.class) == Integer.class
   *     wrap(Integer.class) == Integer.class
   *     wrap(String.class) == String.class
   * </pre>
   */
  public static <T> Class<T> wrap(Class<T> type) {
    checkNotNull(type);

    // cast is safe: long.class and Long.class are both of type Class<Long>
    @SuppressWarnings("unchecked")
    Class<T> wrapped = (Class<T>) PRIMITIVE_TO_WRAPPER_TYPE.get(type);
    return (wrapped == null) ? type : wrapped;
  }

  /**
   * Returns the corresponding primitive type of {@code type} if it is a
   * wrapper type; otherwise returns {@code type} itself. Idempotent.
   * <pre>
   *     unwrap(Integer.class) == int.class
   *     unwrap(int.class) == int.class
   *     unwrap(String.class) == String.class
   * </pre>
   */
  public static <T> Class<T> unwrap(Class<T> type) {
    checkNotNull(type);

    // cast is safe: long.class and Long.class are both of type Class<Long>
    @SuppressWarnings("unchecked")
    Class<T> unwrapped = (Class<T>) WRAPPER_TO_PRIMITIVE_TYPE.get(type);
    return (unwrapped == null) ? type : unwrapped;
  }
}