| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you 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 org.apache.beam.sdk.values; |
| |
| import static org.apache.beam.vendor.guava.v20_0.com.google.common.base.Preconditions.checkArgument; |
| |
| import java.lang.reflect.ParameterizedType; |
| import java.lang.reflect.Type; |
| import java.lang.reflect.TypeVariable; |
| |
| /** |
| * Captures a free type variable that can be used in {@link TypeDescriptor#where}. For example: |
| * |
| * <pre>{@code |
| * static <T> TypeDescriptor<List<T>> listOf(Class<T> elementType) { |
| * return new TypeDescriptor<List<T>>() {} |
| * .where(new TypeParameter<T>() {}, elementType); |
| * } |
| * }</pre> |
| */ |
| public abstract class TypeParameter<T> { |
| final TypeVariable<?> typeVariable; |
| |
| public TypeParameter() { |
| Type superclass = getClass().getGenericSuperclass(); |
| checkArgument(superclass instanceof ParameterizedType, "%s isn't parameterized", superclass); |
| typeVariable = (TypeVariable<?>) ((ParameterizedType) superclass).getActualTypeArguments()[0]; |
| } |
| |
| @Override |
| public int hashCode() { |
| return typeVariable.hashCode(); |
| } |
| |
| @Override |
| public boolean equals(Object obj) { |
| if (!(obj instanceof TypeParameter)) { |
| return false; |
| } |
| TypeParameter<?> that = (TypeParameter<?>) obj; |
| return typeVariable.equals(that.typeVariable); |
| } |
| |
| @Override |
| public String toString() { |
| return typeVariable.toString(); |
| } |
| } |