我们必须一直为日志输出构建字符串等等。在JDK版本中,我们已经学习了什么时候使用StringBuffer(许多追加,线程安全)和StringBuilder(许多追加,非线程安全)。
使用String.format()有什么建议?它是有效的,还是我们被迫坚持在性能很重要的一行程序中使用连接?
例如,丑陋的老式风格,
String s = "What do you get if you multiply " + varSix + " by " + varNine + "?";
vs.整洁的新样式(字符串。格式,可能更慢),
String s = String.format("What do you get if you multiply %d by %d?", varSix, varNine);
注意:我的特定用例是代码中的数百个“一行”日志字符串。它们不涉及循环,所以StringBuilder太重量级了。我对String.format()特别感兴趣。
To expand/correct on the first answer above, it's not translation that String.format would help with, actually.
What String.format will help with is when you're printing a date/time (or a numeric format, etc), where there are localization(l10n) differences (ie, some countries will print 04Feb2009 and others will print Feb042009).
With translation, you're just talking about moving any externalizable strings (like error messages and what-not) into a property bundle so that you can use the right bundle for the right language, using ResourceBundle and MessageFormat.
Looking at all the above, I'd say that performance-wise, String.format vs. plain concatenation comes down to what you prefer. If you prefer looking at calls to .format over concatenation, then by all means, go with that.
After all, code is read a lot more than it's written.
我只是修改了hhafez的测试,以包括StringBuilder。StringBuilder比String快33倍。格式使用jdk 1.6.0_10客户端XP。使用-server开关将该因子降低到20。
public class StringTest {
public static void main( String[] args ) {
test();
test();
}
private static void test() {
int i = 0;
long prev_time = System.currentTimeMillis();
long time;
for ( i = 0; i < 1000000; i++ ) {
String s = "Blah" + i + "Blah";
}
time = System.currentTimeMillis() - prev_time;
System.out.println("Time after for loop " + time);
prev_time = System.currentTimeMillis();
for ( i = 0; i < 1000000; i++ ) {
String s = String.format("Blah %d Blah", i);
}
time = System.currentTimeMillis() - prev_time;
System.out.println("Time after for loop " + time);
prev_time = System.currentTimeMillis();
for ( i = 0; i < 1000000; i++ ) {
new StringBuilder("Blah").append(i).append("Blah");
}
time = System.currentTimeMillis() - prev_time;
System.out.println("Time after for loop " + time);
}
}
虽然这听起来可能很激烈,但我认为它只在极少数情况下相关,因为绝对数字非常低:100万个简单字符串对应4个s。格式调用是可以的-只要我使用他们的日志或类似的。
更新:正如sjbotha在评论中指出的,StringBuilder测试是无效的,因为它缺少最后的. tostring()。
在我的机器上,从String.format(.)到StringBuilder的正确加速因子是23(使用-server开关时为16)。