org.apache.hadoop.util.StringInterner.java Source code

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Here is the source code for org.apache.hadoop.util.StringInterner.java

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/**
 * 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.hadoop.util;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;

import com.google.common.collect.Interner;
import com.google.common.collect.Interners;

/**
 * Provides string interning utility methods. For weak interning,
 * we use the standard String.intern() call, that performs very well
 * (no problems with PermGen overflowing, etc.) starting from JDK 7.
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public class StringInterner {

    /**
     * Retains a strong reference to each string instance it has interned.
     */
    private final static Interner<String> STRONG_INTERNER = Interners.newStrongInterner();

    /**
     * Interns and returns a reference to the representative instance 
     * for any of a collection of string instances that are equal to each other.
     * Retains strong reference to the instance, 
     * thus preventing it from being garbage-collected. 
     * 
     * @param sample string instance to be interned
     * @return strong reference to interned string instance
     */
    public static String strongIntern(String sample) {
        if (sample == null) {
            return null;
        }
        return STRONG_INTERNER.intern(sample);
    }

    /**
     * Interns and returns a reference to the representative instance 
     * for any of a collection of string instances that are equal to each other.
     * Retains weak reference to the instance, 
     * and so does not prevent it from being garbage-collected.
     * 
     * @param sample string instance to be interned
     * @return weak reference to interned string instance
     */
    public static String weakIntern(String sample) {
        if (sample == null) {
            return null;
        }
        return sample.intern();
    }

    /**
     * Interns all the strings in the given array in place,
     * returning the same array.
     */
    public static String[] internStringsInArray(String[] strings) {
        for (int i = 0; i < strings.length; i++) {
            strings[i] = weakIntern(strings[i]);
        }
        return strings;
    }

}