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A library to load and index GTFS feeds of arbitrary size using disk-backed storage
There is a newer version: 6.2.0
package com.conveyal.gtfs.util;

import com.google.common.collect.Maps;

import java.io.Serializable;
import java.util.Arrays;
import java.util.BitSet;
import java.util.Map;

/**
 * Does the same thing as String.intern, but for several different types.
 * Java's String.intern uses perm gen space and is broken anyway.
 */
public class Deduplicator implements Serializable {
    private static final long serialVersionUID = 20140524L;

    private final Map canonicalIntArrays = Maps.newHashMap();
    private final Map canonicalStrings = Maps.newHashMap();
    private final Map canonicalBitSets = Maps.newHashMap();
    private final Map canonicalStringArrays = Maps.newHashMap();

    /** Free up any memory used by the deduplicator. */
    public void reset() {
        canonicalIntArrays.clear();
        canonicalStrings.clear();
        canonicalBitSets.clear();
        canonicalStringArrays.clear();
    }

    /** Used to deduplicate time and stop sequence arrays. The same times may occur in many trips. */
    public int[] deduplicateIntArray(int[] original) {
        if (original == null) return null;
        IntArray intArray = new IntArray(original);
        IntArray canonical = canonicalIntArrays.get(intArray);
        if (canonical == null) {
            canonical = intArray;
            canonicalIntArrays.put(canonical, canonical);
        }
        return canonical.array;
    }

    public String deduplicateString(String original) {
        if (original == null) return null;
        String canonical = canonicalStrings.get(original);
        if (canonical == null) {
            canonical = new String(original.toCharArray()); // Trim String if necessary (older JDKs)
            canonicalStrings.put(canonical, canonical);
        }
        return canonical;
    }

    public BitSet deduplicateBitSet(BitSet original) {
        if (original == null) return null;
        BitSet canonical = canonicalBitSets.get(original);
        if (canonical == null) {
            canonical = original;
            canonicalBitSets.put(canonical, canonical);
        }
        return canonical;
    }

    public String[] deduplicateStringArray(String[] original) {
        if (original == null) return null;
        StringArray canonical = canonicalStringArrays.get(new StringArray(original, false));
        if (canonical == null) {
            canonical = new StringArray(original, true);
            canonicalStringArrays.put(canonical, canonical);
        }
        return canonical.array;
    }

    /** A wrapper for a primitive int array. This is insane but necessary in Java. */
    private class IntArray implements Serializable {
        private static final long serialVersionUID = 20140524L;
        final int[] array;
        IntArray(int[] array) {
            this.array = array;
        }
        @Override
        public boolean equals (Object other) {
            if (other instanceof IntArray) {
                return Arrays.equals(array, ((IntArray) other).array);
            } else return false;
        }
        @Override
        public int hashCode() {
            return Arrays.hashCode(array);
        }
    }

    /** A wrapper for a String array. Optionally, the individual Strings may be deduplicated too. */
    private class StringArray implements Serializable {
        private static final long serialVersionUID = 20140524L;
        final String[] array;
        StringArray(String[] array, boolean deduplicateStrings) {
            if (deduplicateStrings) {
                this.array = new String[array.length];
                for (int i = 0; i < array.length; i++) {
                    this.array[i] = deduplicateString(array[i]);
                }
            } else this.array = array;
        }
        @Override
        public boolean equals (Object other) {
            if (other instanceof StringArray) {
                return Arrays.equals(array, ((StringArray) other).array);
            } else return false;
        }
        @Override
        public int hashCode() {
            return Arrays.hashCode(array);
        }
    }
}