StringPool.java

package com.google.gson.stream;

/**
 * A pool of string instances. Unlike the {@link String#intern() VM's interned strings}, this pool
 * provides no guarantee of reference equality. It is intended only to save allocations. This class
 * is not thread safe.
 */
final class StringPool {

    private final String[] pool = new String[512];

    /**
     * Returns a string equal to {@code new String(array, start, length)}.
     */
    public String get(char[] array, int start, int length) {
        // Compute an arbitrary hash of the content
        int hashCode = 0;
        for (int i = start; i < start + length; i++) {
            hashCode = (hashCode * 31) + array[i];
        }

        // Pick a bucket using Doug Lea's supplemental secondaryHash function (from HashMap)
        hashCode ^= (hashCode >>> 20) ^ (hashCode >>> 12);
        hashCode ^= (hashCode >>> 7) ^ (hashCode >>> 4);
        int index = hashCode & (pool.length - 1);

        String pooled = pool[index];
        if (pooled == null || pooled.length() != length) {
            String result = new String(array, start, length);
            pool[index] = result;
            return result;
        }

        for (int i = 0; i < length; i++) {
            if (pooled.charAt(i) != array[start + i]) {
                String result = new String(array, start, length);
                pool[index] = result;
                return result;
            }
        }

        return pooled;
    }
}