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デブサミ2008レポート
http://www.atmarkit.co.jp/fjava/special/devsummit2008/devsummit2008_2.html

つーわけで？デモで使ったコード。
（残りは、デブサミのダウンロード資料で）

switch vs array vs Map
(arrayの勝ち)

package sample;
import java.util.HashMap;

import java.util.Map;
import org.seasar.framework.log.Logger;
public class SwitchVsArrayVsMap {

	public static void main(String[] args) {
		System.gc();

		long start = System.currentTimeMillis();

		for (int i = 0; i < ループ回数; i++) {

			getWithSwitch(i % 10);

		}

		long end = System.currentTimeMillis();

		logger.debug("switch : " + (end - start));
		System.gc();

		start = System.currentTimeMillis();

		for (int i = 0; i < ループ回数; i++) {

			getFromArray(i % 10);

		}

		end = System.currentTimeMillis();

		logger.debug("array  : " + (end - start));
		System.gc();

		start = System.currentTimeMillis();

		for (int i = 0; i < ループ回数; i++) {

			getFromMap(i % 10);

		}

		end = System.currentTimeMillis();

		logger.debug("Map    : " + (end - start));

	}
	private static String getFromMap(int i) {

		return map.get(i);

	}
	private static String getWithSwitch(int key) {

		switch (key) {

		case 0:

			return foo;

		case 1:

			return bar;

		case 2:

			return baz;

		case 3:

			return qux;

		case 4:

			return quux;

		case 5:

			return garply;

		case 6:

			return waldo;

		case 7:

			return fred;

		case 8:

			return plugh;

		case 9:

			return xyzzy;

		}

		return null;

	}
	private static String getFromArray(int key) {

		return array[key];

	}
	private static final String foo = "foo";
	private static final String bar = "bar";
	private static final String baz = "baz";
	private static final String qux = "qux";
	private static final String quux = "quux";
	private static final String garply = "garply";
	private static final String waldo = "waldo";
	private static final String fred = "fred";
	private static final String plugh = "plugh";
	private static final String xyzzy = "xyzzy";
	private static final String[] array = { foo, bar, baz, qux, quux, garply,

			waldo, fred, plugh, xyzzy };
	private static final Map map = new HashMap();
	static {

		map.put(0, foo);

		map.put(1, bar);

		map.put(2, baz);

		map.put(3, qux);

		map.put(4, quux);

		map.put(5, garply);

		map.put(6, waldo);

		map.put(7, fred);

		map.put(8, plugh);

		map.put(9, xyzzy);

	}
	private static final Logger logger = Logger

			.getLogger(SwitchVsArrayVsMap.class);
	private static final int ループ回数 = 100000000;

}

charAt(その1)
(charAtの勝ち)

package sample;
public class StartsWithVsCharAt_1 {

	public static void main(String[] args) {
		String foo = "foo";

		String startsWithString = "f";

		char startsWithChar = 'f';

		final int ループ回数 = 200000000;

		@SuppressWarnings("unused")

		boolean isStart;
		long start = System.currentTimeMillis();

		for (int i = 0; i < ループ回数; i++) {

			isStart = foo.startsWith(startsWithString);

		}

		long end = System.currentTimeMillis();

		System.out.println("String#startsWith : " + (end - start));
		start = System.currentTimeMillis();

		for (int i = 0; i < ループ回数; i++) {

			isStart = foo.charAt(0) == startsWithChar;

		}

		end = System.currentTimeMillis();

		System.out.println("String#charAt     : " + (end - start));

	}

}

charAt(その2)
(まだcharAtの勝ち)

package sample;
import org.seasar.framework.log.Logger;
/**

 * 20文字

 */

public class StartsWithVsCharAt_3 {

	public static void main(String[] args) {

		String foo = "01234567890123456789";

		String startsWithString = "01234567890123456789";

		@SuppressWarnings("unused")

		boolean isStart;
		long start = System.currentTimeMillis();

		for (int i = 0; i < ループ回数; i++) {

			isStart = foo.startsWith(startsWithString);

		}

		long end = System.currentTimeMillis();

		logger.debug("String#startsWith : " + (end - start));
		start = System.currentTimeMillis();

		for (int i = 0; i < ループ回数; i++) {

			isStart = (foo.charAt(0) == '0' && foo.charAt(1) == '1'

					&& foo.charAt(2) == '2' && foo.charAt(3) == '3'

					&& foo.charAt(4) == '4' && foo.charAt(5) == '5'

					&& foo.charAt(6) == '6' && foo.charAt(7) == '7'

					&& foo.charAt(8) == '8' && foo.charAt(9) == '9'

					&& foo.charAt(10) == '0' && foo.charAt(11) == '1'

					&& foo.charAt(12) == '2' && foo.charAt(13) == '3'

					&& foo.charAt(14) == '4' && foo.charAt(15) == '5'

					&& foo.charAt(16) == '6' && foo.charAt(17) == '7'

					&& foo.charAt(18) == '8' && foo.charAt(19) == '9');

		}

		end = System.currentTimeMillis();

		logger.debug("String#charAt     : " + (end - start));
	}
	private static final Logger logger = Logger

			.getLogger(StartsWithVsCharAt_3.class);
	private static final int ループ回数 = 50000000;

}

最後は、当たり前かな〜
array vs tempValue
(tempValueの勝ち)

package sample;
import org.seasar.framework.log.Logger;
public class ArrayVsTempValue {
	public static void main(String[] args) {

		final int ループ回数 = 100000000;

		int[] array = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
		long start = System.currentTimeMillis();

		for (int i = 0; i < ループ回数; i++) {

			array[0] += 1;

			array[0] += 2;

			array[0] += 3;

			array[0] += 4;

			array[0] += 5;

		}

		long end = System.currentTimeMillis();

		logger.debug("array[index] : " + (end - start));
		start = System.currentTimeMillis();

		for (int i = 0; i < ループ回数; i++) {

			int temporary = array[0];

			temporary += 1;

			temporary += 2;

			temporary += 3;

			temporary += 4;

			temporary += 5;

			array[0] = temporary;

		}

		end = System.currentTimeMillis();

		logger.debug("temporaryValue : " + (end - start));

	}
	private static final Logger logger = Logger.getLogger(ArrayVsTempValue.class);

}