| // 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.impala.common; |
| |
| import java.util.Set; |
| |
| import com.google.common.base.Preconditions; |
| import com.google.common.collect.Sets; |
| |
| /** |
| * Abstract class representing an alias generator. It uses a prefix and a |
| * monotonically increasing counter to generate new aliases. Classes extending |
| * this class are responsible for initializing the prefix. |
| */ |
| public abstract class AliasGenerator { |
| private int numGeneratedAliases_ = 1; |
| protected String aliasPrefix_ = null; |
| protected Set<String> usedAliases_ = Sets.newHashSet(); |
| |
| /** |
| * Return the next available alias. |
| */ |
| public String getNextAlias() { |
| Preconditions.checkNotNull(aliasPrefix_); |
| while (true) { |
| String candidateAlias = aliasPrefix_ + Integer.toString(numGeneratedAliases_++); |
| if (usedAliases_.add(candidateAlias)) return candidateAlias; |
| if (numGeneratedAliases_ < 0) { |
| throw new IllegalStateException("Overflow occured during alias generation."); |
| } |
| } |
| } |
| } |