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Guava library, with additional type annotations for verification
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/*
* Copyright (C) 2011 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.reflect;
import static com.google.common.base.Preconditions.checkArgument;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.signedness.qual.UnknownSignedness;
/**
* Captures a free type variable that can be used in {@link TypeToken#where}. For example:
*
* {@code
* static TypeToken> listOf(Class elementType) {
* return new TypeToken>() {}
* .where(new TypeParameter() {}, elementType);
* }
* }
*
* @author Ben Yu
* @since 12.0
*/
@ElementTypesAreNonnullByDefault
/*
* A nullable bound would let users create a TypeParameter instance for a parameter with a nullable
* bound. However, it would also let them create `new TypeParameter<@Nullable T>() {}`, which
* wouldn't behave as users might expect. Additionally, it's not clear how the TypeToken API could
* support even a "normal" `TypeParameter` when `` has a nullable bound. (See the discussion
* on TypeToken.where.) So, in the interest of failing fast and encouraging the user to switch to a
* non-null bound if possible, let's require a non-null bound here.
*
* TODO(cpovirk): Elaborate on "wouldn't behave as users might expect."
*/
public abstract class TypeParameter extends TypeCapture {
final TypeVariable typeVariable;
protected TypeParameter() {
Type type = capture();
checkArgument(type instanceof TypeVariable, "%s should be a type variable.", type);
this.typeVariable = (TypeVariable) type;
}
@Override
public final int hashCode(@UnknownSignedness TypeParameter this) {
return typeVariable.hashCode();
}
@Override
public final boolean equals(@CheckForNull Object o) {
if (o instanceof TypeParameter) {
TypeParameter that = (TypeParameter) o;
return typeVariable.equals(that.typeVariable);
}
return false;
}
@Override
public String toString() {
return typeVariable.toString();
}
}