AliasGenerator.java

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// Copyright 2014 Cloudera Inc.
//
// 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.cloudera.impala.common;

import java.util.Set;

import com.google.common.base.Preconditions;
import com.google.common.collect.Sets;

public abstract class AliasGenerator {
  private int numGeneratedAliases_ = 1;
  protected String aliasPrefix_ = null;
  protected Set<String> usedAliases_ = Sets.newHashSet();

  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.");
      }
    }
  }
}