001 /*
002 * Copyright (C) 2011 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.reflect;
018
019 import static com.google.common.base.Preconditions.checkArgument;
020 import static com.google.common.base.Preconditions.checkNotNull;
021
022 import com.google.common.annotations.Beta;
023
024 import java.lang.reflect.Type;
025 import java.lang.reflect.TypeVariable;
026
027 /**
028 * Captures a free type variable that can be used in {@link TypeToken#where}.
029 * For example: <pre> {@code
030 *
031 * static <T> TypeToken<List<T>> listOf(Class<T> elementType) {
032 * return new TypeToken<List<T>>() {}
033 * .where(new TypeParameter<T>() {}, elementType);
034 * }
035 * }</pre>
036 *
037 * @author Ben Yu
038 * @since 12.0
039 */
040 @Beta
041 public abstract class TypeParameter<T> extends TypeCapture<T> {
042
043 final TypeVariable<?> typeVariable;
044
045 private TypeParameter(TypeVariable<?> typeVariable) {
046 this.typeVariable = checkNotNull(typeVariable);
047 }
048
049 protected TypeParameter() {
050 Type type = capture();
051 checkArgument(type instanceof TypeVariable, "%s should be a type variable.", type);
052 this.typeVariable = (TypeVariable<?>) type;
053 }
054
055 @Override public final int hashCode() {
056 return typeVariable.hashCode();
057 }
058
059 @Override public final boolean equals(Object o) {
060 if (o instanceof TypeParameter) {
061 TypeParameter<?> that = (TypeParameter<?>) o;
062 return typeVariable.equals(that.typeVariable);
063 }
064 return false;
065 }
066
067 @Override public String toString() {
068 return typeVariable.toString();
069 }
070 }