比较如下两个正则表达式:
(?:.*?(?:\\s|,)+)*no\\s+air\\s+conditioning.*? (?:.*?(?:\\s|,)+)?no\\s+air\\s+conditioning.*?
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区别仅仅在于*和?的区别,一字之差性能就相差很多:前者是35699.334;后者是108.686
完整测试代码:
String TEST_VALUE = "ABS, traction control, front and side airbags, Isofix child seat anchor points, no air conditioning, electric windows, \r\nelectrically operated door mirrors"; double start = System.nanoTime(); Pattern pattern = Pattern.compile("^(?:.*?(?:\\s|,)+)*no\\s+air\\s+conditioning.*$"); assertTrue(pattern.matcher(TEST_VALUE).matches()); double end = System.nanoTime(); LOGGER.info("Took {} micros", (end - start) / (1000 ));
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两分钟以后这个程序还在运行,已经堵塞了CPU: