import java.util.ArrayList;
import java.util.List; import org.apache.commons.lang.StringUtils;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory; public class TestString { private final Logger logger = LoggerFactory.getLogger(this.getClass()); @Test
public void testPlus() {
String s = "";
long ts = System.currentTimeMillis();
for (int i = 0; i < 10000; i++) {
s = s + String.valueOf(i);
}
long te = System.currentTimeMillis();
logger.info("+ cost {} ms", te - ts);
} @Test
public void testConcat() {
String s = "";
long ts = System.currentTimeMillis();
for (int i = 0; i < 10000; i++) {
s = s.concat(String.valueOf(i));
}
long te = System.currentTimeMillis();
logger.info("concat cost {} ms", te - ts);
} @Test
public void testJoin() {
List<String> list = new ArrayList<String>();
long ts = System.currentTimeMillis();
for (int i = 0; i < 10000; i++) {
list.add(String.valueOf(i));
}
StringUtils.join(list, "");
long te = System.currentTimeMillis();
logger.info("StringUtils.join cost {} ms", te - ts);
} @Test
public void testStringBuffer() {
StringBuffer sb = new StringBuffer();
long ts = System.currentTimeMillis();
for (int i = 0; i < 10000; i++) {
sb.append(String.valueOf(i));
}
sb.toString();
long te = System.currentTimeMillis();
logger.info("StringBuffer cost {} ms", te - ts);
} @Test
public void testStringBuilder() {
StringBuilder sb = new StringBuilder();
long ts = System.currentTimeMillis();
for (int i = 0; i < 100000; i++) {
sb.append(String.valueOf(i));
}
sb.toString();
long te = System.currentTimeMillis();
logger.info("StringBuilder cost {} ms", te - ts);
}
}
运行结果如下:
11:00:22,359 INFO TestString:23 - + cost 1828 ms
11:00:22,921 INFO TestString:34 - concat cost 562 ms
11:00:22,937 INFO TestString:46 - StringUtils.join cost 16 ms
11:00:22,968 INFO TestString:58 - StringBuffer cost 31 ms
11:00:23,031 INFO TestString:70 - StringBuilder cost 63 ms
要特别注意的是:
StringBuilder 循环的次数是其它的10倍,如果是一样,那么返回 0,可见StringBuilder 的速度之快。
总结:
用+的方式效率最差,concat由于是内部机制实现,比+的方式好了不少。
Join 和 StringBuffer,相差不大,Join方式要快些,可见这种JavaScript中快速拼接字符串的方式在Java中也非常适用。
StringBuilder 的速度最快,但其有线程安全的问题,而且只有JDK5支持。
基于使用StringUtils.join需导入第三方包,使用StringBuilder可能有线程安全的问题,实际使用的,我一般首选StringBuffer