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 }