Update #0 - First Release

sources/main/java/com/google/common/primitives/Primitives.java

@@ -0,0 +1,137 @@
+/*
+ * 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;
+	}
+}