String#split() と Pattern#split() の性能を比較するデモコード。

StringSplitDemo.java

package biz.k11i.demo;

import java.lang.management.GarbageCollectorMXBean;
import java.lang.management.ManagementFactory;
import java.util.List;
import java.util.regex.Pattern;

public class StringSplitDemo {
    public static void main(String[] args) {
        if (args.length < 2) {
            return;
        }

        final int LOOP_COUNT = 1000 * 1000 * 20;
        String text = "The quick brown fox jumps over the lazy dog.";
        String[] patterns = { " ", "\\s", "[ \\t\\n\\x0B\\f\\r]", " |\\t|\\n|\\x0B|\\f|\\r" };

        String pattern = patterns[Integer.valueOf(args[1])];

        if ("string".equals(args[0])) {
            profileStringSplit(text, pattern, LOOP_COUNT);
        } else {
            profilePatternSplit(text, pattern, LOOP_COUNT);
        }

        List<GarbageCollectorMXBean> beans = ManagementFactory.getGarbageCollectorMXBeans();
        for (GarbageCollectorMXBean b : beans) {
            if ("PS Scavenge".equals(b.getName())) {
                System.out.println(String.format("%s\t%s", b.getName(),b.getCollectionCount()));
            }
        }
    }

    public static void profileStringSplit(String text, String pattern, int loopCount) {
        long begin, end;

        begin = System.currentTimeMillis() + 1000;
        while (System.currentTimeMillis() < begin) {
            // do nothing
        }

        for (int i = 0; i < loopCount; i++) {
            text.split(pattern);
        }
        end = System.currentTimeMillis();

        System.out.println(String.format("text : %s, pattern : \"%s\"", text, pattern));
        System.out.println(String.format("String#split()\t%d", end - begin));
        System.out.println();
    }

    public static void profilePatternSplit(String text, String pattern, int loopCount) {
        long begin, end;

        begin = System.currentTimeMillis() + 1000;
        while (System.currentTimeMillis() < begin) {
            // do nothing
        }

        Pattern p = Pattern.compile(pattern);
        for (int i = 0; i < loopCount; i++) {
            p.split(text);
        }
        end = System.currentTimeMillis();

        System.out.println(String.format("text : %s, pattern : \"%s\"", text, pattern));
        System.out.println(String.format("Pattern#split()\t%d", end - begin));
        System.out.println();
    }
}