Merge "Copy StringPool to framework"

package android.util;

import libcore.internal.StringPool;

import com.android.internal.util.StringPool;

import java.io.Closeable;

import java.io.EOFException;

/*

 * Copyright (C) 2010 The Android Open Source Project

 *

 * 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.android.internal.util;

/**

 * 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.

 *

 * @hide

 */

public final class StringPool {

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

    /**

     * Constructs string pool.

     */

    public StringPool() {

    }

    private static boolean contentEquals(String s, char[] chars, int start, int length) {

        if (s.length() != length) {

            return false;

        }

        for (int i = 0; i < length; i++) {

            if (chars[start + i] != s.charAt(i)) {

                return false;

            }

        }

        return true;

    }

    /**

     * Returns a string equal to {@code new String(array, start, length)}.

     *

     * @param array  buffer containing string chars

     * @param start  offset in {@code array} where string starts

     * @param length length of string

     * @return 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 & (mPool.length - 1);

        String pooled = mPool[index];

        if (pooled != null && contentEquals(pooled, array, start, length)) {

            return pooled;

        }

        String result = new String(array, start, length);

        mPool[index] = result;

        return result;

    }

}

/*

 * Copyright (C) 2010 The Android Open Source Project

 *

 * 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.android.internal.util;

import android.test.AndroidTestCase;

import android.test.suitebuilder.annotation.SmallTest;

@SmallTest

public final class StringPoolTest extends AndroidTestCase {

    public void testStringPool() {

        StringPool stringPool = new StringPool();

        String bcd = stringPool.get(new char[] { 'a', 'b', 'c', 'd', 'e' }, 1, 3);

        assertEquals("bcd", bcd);

        assertSame(bcd, stringPool.get(new char[] { 'a', 'b', 'c', 'd', 'e' }, 1, 3));

    }

    public void testHashCollision() {

        StringPool stringPool = new StringPool();

        char[] a = { (char) 1, (char) 0 };

        char[] b = { (char) 0, (char) 31 };

        assertEquals(new String(a).hashCode(), new String(b).hashCode());

        String aString = stringPool.get(a, 0, 2);

        assertEquals(new String(a), aString);

        String bString = stringPool.get(b, 0, 2);

        assertEquals(new String(b), bString);

        assertSame(bString, stringPool.get(b, 0, 2));

        assertNotSame(aString, stringPool.get(a, 0, 2));

    }

}