/*
 * 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 static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;

import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;

/**
 * Captures a free type variable that can be used in {@link TypeToken#where}.
 * For example: <pre>   {@code
 *
 *   static <T> TypeToken<List<T>> listOf(Class<T> elementType) {
 *     return new TypeToken<List<T>>() {}
 *         .where(new TypeParameter<T>() {}, elementType);
 *   }
 * }</pre>
 *
 * @author Ben Yu
 * @since 12.0
 */
@Beta
public abstract class TypeParameter<T> extends TypeCapture<T> {

  final TypeVariable<?> typeVariable;

  private TypeParameter(TypeVariable<?> typeVariable) {
    this.typeVariable = checkNotNull(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() {
    return typeVariable.hashCode();
  }

  @Override public final boolean equals(Object o) {
    if (o instanceof TypeParameter) {
      TypeParameter<?> that = (TypeParameter<?>) o;
      return typeVariable.equals(that.typeVariable);
    }
    return false;
  }

  @Override public String toString() {
    return typeVariable.toString();
  }
}