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Java example source code file (Primitives.java)

This example Java source code file (Primitives.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.

Learn more about this Java project at its project page.

Java - Java tags/keywords

class, gwtincompatible, hashmap, map, primitive_to_wrapper_type, primitives, set, suppresswarnings, util, wrapper_to_primitive_type

The Primitives.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.primitives;

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

import com.google.common.annotations.GwtIncompatible;

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
 */
@GwtIncompatible
public final class Primitives {
  private Primitives() {}

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

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

  // Sad that we can't use a BiMap. :(

  static {
    Map<Class> primToWrap = new HashMap, Class>(16);
    Map<Class> wrapToPrim = new HashMap, 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> forward,
      Map<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 wrap(Class type) {
    checkNotNull(type);

    // cast is safe: long.class and Long.class are both of type Class<Long>
    @SuppressWarnings("unchecked")
    Class<T> wrapped = (Class) 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 unwrap(Class type) {
    checkNotNull(type);

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

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