1 /*
2 * Copyright (C) 2011 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.google.common.reflect;
18
19 import static com.google.common.base.Preconditions.checkArgument;
20
21 import com.google.common.annotations.Beta;
22
23 import java.lang.reflect.Type;
24 import java.lang.reflect.TypeVariable;
25
26 import javax.annotation.Nullable;
27
28 /**
29 * Captures a free type variable that can be used in {@link TypeToken#where}.
30 * For example:
31 *
32 * <pre> {@code
33 * static <T> TypeToken<List<T>> listOf(Class<T> elementType) {
34 * return new TypeToken<List<T>>() {}
35 * .where(new TypeParameter<T>() {}, elementType);
36 * }}</pre>
37 *
38 * @author Ben Yu
39 * @since 12.0
40 */
41 @Beta
42 public abstract class TypeParameter<T> extends TypeCapture<T> {
43
44 final TypeVariable<?> typeVariable;
45
46 protected TypeParameter() {
47 Type type = capture();
48 checkArgument(type instanceof TypeVariable, "%s should be a type variable.", type);
49 this.typeVariable = (TypeVariable<?>) type;
50 }
51
52 @Override public final int hashCode() {
53 return typeVariable.hashCode();
54 }
55
56 @Override public final boolean equals(@Nullable Object o) {
57 if (o instanceof TypeParameter) {
58 TypeParameter<?> that = (TypeParameter<?>) o;
59 return typeVariable.equals(that.typeVariable);
60 }
61 return false;
62 }
63
64 @Override public String toString() {
65 return typeVariable.toString();
66 }
67 }