使用String和使用String之间有明显的区别吗?格式和字符串连接在Java?
我倾向于使用String。格式,但偶尔会滑倒和使用连接。我想知道哪个比哪个好。
在我看来,String。Format让你在“格式化”字符串时更强大;连接意味着您不必担心不小心输入了额外的%s或遗漏了一个。
字符串。格式也更短。
哪一个更容易读,取决于你的大脑如何工作。
使用String和使用String之间有明显的区别吗?格式和字符串连接在Java?
我倾向于使用String。格式,但偶尔会滑倒和使用连接。我想知道哪个比哪个好。
在我看来,String。Format让你在“格式化”字符串时更强大;连接意味着您不必担心不小心输入了额外的%s或遗漏了一个。
字符串。格式也更短。
哪一个更容易读,取决于你的大脑如何工作。
当前回答
哪一个更容易读,取决于你的大脑如何工作。
你已经得到答案了。
这是个人喜好的问题。
我认为,字符串连接稍微快一些,但这应该可以忽略不计。
其他回答
可能会有明显的差别。
字符串。Format相当复杂,在底层使用正则表达式,所以不要习惯在任何地方使用它,只在需要它的地方使用。
StringBuilder会快一个数量级(这里有人已经指出了)。
It takes a little time to get used to String.Format, but it's worth it in most cases. In the world of NRA (never repeat anything) it's extremely useful to keep your tokenized messages (logging or user) in a Constant library (I prefer what amounts to a static class) and call them as necessary with String.Format regardless of whether you are localizing or not. Trying to use such a library with a concatenation method is harder to read, troubleshoot, proofread, and manage with any any approach that requires concatenation. Replacement is an option, but I doubt it's performant. After years of use, my biggest problem with String.Format is the length of the call is inconveniently long when I'm passing it into another function (like Msg), but that's easy to get around with a custom function to serve as an alias.
由于有关于性能的讨论,我想我应该添加一个包含StringBuilder的比较。事实上,它比concat更快,当然也比String更快。格式选项。
为了使这成为一种苹果对苹果的比较,我在循环中而不是在外部实例化了一个新的StringBuilder(这实际上比只实例化一个更快,这很可能是由于在一个构建器的末尾为循环追加重新分配空间的开销)。
String formatString = "Hi %s; Hi to you %s";
long start = System.currentTimeMillis();
for (int i = 0; i < 1000000; i++) {
String s = String.format(formatString, i, +i * 2);
}
long end = System.currentTimeMillis();
log.info("Format = " + ((end - start)) + " millisecond");
start = System.currentTimeMillis();
for (int i = 0; i < 1000000; i++) {
String s = "Hi " + i + "; Hi to you " + i * 2;
}
end = System.currentTimeMillis();
log.info("Concatenation = " + ((end - start)) + " millisecond");
start = System.currentTimeMillis();
for (int i = 0; i < 1000000; i++) {
StringBuilder bldString = new StringBuilder("Hi ");
bldString.append(i).append("; Hi to you ").append(i * 2);
}
end = System.currentTimeMillis();
log.info("String Builder = " + ((end - start)) + " millisecond");
2012-01-11 16:30:46,058 INFO [TestMain] - Format = 1416毫秒 2012-01-11 16:30:46,190 INFO [TestMain] -连接= 134毫秒 2012-01-11 16:30:46,313 INFO [TestMain] - String Builder = 117毫秒
这是一个以毫秒为单位的多个样本大小的测试。
public class Time {
public static String sysFile = "/sys/class/camera/rear/rear_flash";
public static String cmdString = "echo %s > " + sysFile;
public static void main(String[] args) {
int i = 1;
for(int run=1; run <= 12; run++){
for(int test =1; test <= 2 ; test++){
System.out.println(
String.format("\nTEST: %s, RUN: %s, Iterations: %s",run,test,i));
test(run, i);
}
System.out.println("\n____________________________");
i = i*3;
}
}
public static void test(int run, int iterations){
long start = System.nanoTime();
for( int i=0;i<iterations; i++){
String s = "echo " + i + " > "+ sysFile;
}
long t = System.nanoTime() - start;
String r = String.format(" %-13s =%10d %s", "Concatenation",t,"nanosecond");
System.out.println(r) ;
start = System.nanoTime();
for( int i=0;i<iterations; i++){
String s = String.format(cmdString, i);
}
t = System.nanoTime() - start;
r = String.format(" %-13s =%10d %s", "Format",t,"nanosecond");
System.out.println(r);
start = System.nanoTime();
for( int i=0;i<iterations; i++){
StringBuilder b = new StringBuilder("echo ");
b.append(i).append(" > ").append(sysFile);
String s = b.toString();
}
t = System.nanoTime() - start;
r = String.format(" %-13s =%10d %s", "StringBuilder",t,"nanosecond");
System.out.println(r);
}
}
TEST: 1, RUN: 1, Iterations: 1
Concatenation = 14911 nanosecond
Format = 45026 nanosecond
StringBuilder = 3509 nanosecond
TEST: 1, RUN: 2, Iterations: 1
Concatenation = 3509 nanosecond
Format = 38594 nanosecond
StringBuilder = 3509 nanosecond
____________________________
TEST: 2, RUN: 1, Iterations: 3
Concatenation = 8479 nanosecond
Format = 94438 nanosecond
StringBuilder = 5263 nanosecond
TEST: 2, RUN: 2, Iterations: 3
Concatenation = 4970 nanosecond
Format = 92976 nanosecond
StringBuilder = 5848 nanosecond
____________________________
TEST: 3, RUN: 1, Iterations: 9
Concatenation = 11403 nanosecond
Format = 287115 nanosecond
StringBuilder = 14326 nanosecond
TEST: 3, RUN: 2, Iterations: 9
Concatenation = 12280 nanosecond
Format = 209051 nanosecond
StringBuilder = 11818 nanosecond
____________________________
TEST: 5, RUN: 1, Iterations: 81
Concatenation = 54383 nanosecond
Format = 1503113 nanosecond
StringBuilder = 40056 nanosecond
TEST: 5, RUN: 2, Iterations: 81
Concatenation = 44149 nanosecond
Format = 1264241 nanosecond
StringBuilder = 34208 nanosecond
____________________________
TEST: 6, RUN: 1, Iterations: 243
Concatenation = 76018 nanosecond
Format = 3210891 nanosecond
StringBuilder = 76603 nanosecond
TEST: 6, RUN: 2, Iterations: 243
Concatenation = 91222 nanosecond
Format = 2716773 nanosecond
StringBuilder = 73972 nanosecond
____________________________
TEST: 8, RUN: 1, Iterations: 2187
Concatenation = 527450 nanosecond
Format = 10291108 nanosecond
StringBuilder = 885027 nanosecond
TEST: 8, RUN: 2, Iterations: 2187
Concatenation = 526865 nanosecond
Format = 6294307 nanosecond
StringBuilder = 591773 nanosecond
____________________________
TEST: 10, RUN: 1, Iterations: 19683
Concatenation = 4592961 nanosecond
Format = 60114307 nanosecond
StringBuilder = 2129387 nanosecond
TEST: 10, RUN: 2, Iterations: 19683
Concatenation = 1850166 nanosecond
Format = 35940524 nanosecond
StringBuilder = 1885544 nanosecond
____________________________
TEST: 12, RUN: 1, Iterations: 177147
Concatenation = 26847286 nanosecond
Format = 126332877 nanosecond
StringBuilder = 17578914 nanosecond
TEST: 12, RUN: 2, Iterations: 177147
Concatenation = 24405056 nanosecond
Format = 129707207 nanosecond
StringBuilder = 12253840 nanosecond
String.format()不仅仅是连接字符串。例如,可以使用String.format()显示特定地区的数字。
然而,如果你不关心本地化,就没有功能上的区别。 也许这个连接比另一个快,但在大多数情况下,它可以忽略不计。