001    /*
002     * Copyright (C) 2007 The Guava Authors
003     *
004     * Licensed under the Apache License, Version 2.0 (the "License");
005     * you may not use this file except in compliance with the License.
006     * You may obtain a copy of the License at
007     *
008     * http://www.apache.org/licenses/LICENSE-2.0
009     *
010     * Unless required by applicable law or agreed to in writing, software
011     * distributed under the License is distributed on an "AS IS" BASIS,
012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013     * See the License for the specific language governing permissions and
014     * limitations under the License.
015     */
016    
017    package com.google.common.primitives;
018    
019    import static com.google.common.base.Preconditions.checkNotNull;
020    
021    import java.util.Collections;
022    import java.util.HashMap;
023    import java.util.Map;
024    import java.util.Set;
025    
026    /**
027     * Contains static utility methods pertaining to primitive types and their
028     * corresponding wrapper types.
029     *
030     * @author Kevin Bourrillion
031     * @since 1.0
032     */
033    public final class Primitives {
034      private Primitives() {}
035    
036      /** A map from primitive types to their corresponding wrapper types. */
037      private static final Map<Class<?>, Class<?>> PRIMITIVE_TO_WRAPPER_TYPE;
038    
039      /** A map from wrapper types to their corresponding primitive types. */
040      private static final Map<Class<?>, Class<?>> WRAPPER_TO_PRIMITIVE_TYPE;
041    
042      // Sad that we can't use a BiMap. :(
043      
044      static {
045        Map<Class<?>, Class<?>> primToWrap = new HashMap<Class<?>, Class<?>>(16);
046        Map<Class<?>, Class<?>> wrapToPrim = new HashMap<Class<?>, Class<?>>(16);
047    
048        add(primToWrap, wrapToPrim, boolean.class, Boolean.class);
049        add(primToWrap, wrapToPrim, byte.class, Byte.class);
050        add(primToWrap, wrapToPrim, char.class, Character.class);
051        add(primToWrap, wrapToPrim, double.class, Double.class);
052        add(primToWrap, wrapToPrim, float.class, Float.class);
053        add(primToWrap, wrapToPrim, int.class, Integer.class);
054        add(primToWrap, wrapToPrim, long.class, Long.class);
055        add(primToWrap, wrapToPrim, short.class, Short.class);
056        add(primToWrap, wrapToPrim, void.class, Void.class);
057    
058        PRIMITIVE_TO_WRAPPER_TYPE = Collections.unmodifiableMap(primToWrap);
059        WRAPPER_TO_PRIMITIVE_TYPE = Collections.unmodifiableMap(wrapToPrim);
060      }
061    
062      private static void add(Map<Class<?>, Class<?>> forward,
063          Map<Class<?>, Class<?>> backward, Class<?> key, Class<?> value) {
064        forward.put(key, value);
065        backward.put(value, key);
066      }
067    
068      /**
069       * Returns an immutable set of all nine primitive types (including {@code
070       * void}). Note that a simpler way to test whether a {@code Class} instance
071       * is a member of this set is to call {@link Class#isPrimitive}.
072       *
073       * @since 3.0
074       */
075      public static Set<Class<?>> allPrimitiveTypes() {
076        return PRIMITIVE_TO_WRAPPER_TYPE.keySet();
077      }
078    
079      /**
080       * Returns an immutable set of all nine primitive-wrapper types (including
081       * {@link Void}).
082       *
083       * @since 3.0
084       */
085      public static Set<Class<?>> allWrapperTypes() {
086        return WRAPPER_TO_PRIMITIVE_TYPE.keySet();
087      }
088    
089      /**
090       * Returns {@code true} if {@code type} is one of the nine
091       * primitive-wrapper types, such as {@link Integer}.
092       *
093       * @see Class#isPrimitive
094       */
095      public static boolean isWrapperType(Class<?> type) {
096        return WRAPPER_TO_PRIMITIVE_TYPE.containsKey(checkNotNull(type));
097      }
098    
099      /**
100       * Returns the corresponding wrapper type of {@code type} if it is a primitive
101       * type; otherwise returns {@code type} itself. Idempotent.
102       * <pre>
103       *     wrap(int.class) == Integer.class
104       *     wrap(Integer.class) == Integer.class
105       *     wrap(String.class) == String.class
106       * </pre>
107       */
108      public static <T> Class<T> wrap(Class<T> type) {
109        checkNotNull(type);
110    
111        // cast is safe: long.class and Long.class are both of type Class<Long>
112        @SuppressWarnings("unchecked")
113        Class<T> wrapped = (Class<T>) PRIMITIVE_TO_WRAPPER_TYPE.get(type);
114        return (wrapped == null) ? type : wrapped;
115      }
116    
117      /**
118       * Returns the corresponding primitive type of {@code type} if it is a
119       * wrapper type; otherwise returns {@code type} itself. Idempotent.
120       * <pre>
121       *     unwrap(Integer.class) == int.class
122       *     unwrap(int.class) == int.class
123       *     unwrap(String.class) == String.class
124       * </pre>
125       */
126      public static <T> Class<T> unwrap(Class<T> type) {
127        checkNotNull(type);
128    
129        // cast is safe: long.class and Long.class are both of type Class<Long>
130        @SuppressWarnings("unchecked")
131        Class<T> unwrapped = (Class<T>) WRAPPER_TO_PRIMITIVE_TYPE.get(type);
132        return (unwrapped == null) ? type : unwrapped;
133      }
134    }