StringBuilder vs String concatenation in toString() in Java
Given the 2 toString() implementations below, which one is preferred:
public String toString(){
return "{a:"+ a + ", b:" + b + ", c: " + c +"}";
}
or
public String toString(){
StringBuilder sb = new StringBuilder(100);
return sb.append("{a:").append(a)
.append(", b:").append(b)
.append(", c:").append(c)
.append("}")
.toString();
}
?
More importantly, given we have only 3 properties it might not make a difference, but at what point would you switch from + concat to StringBuilder ?
Version 1 is preferable because it is shorter and the compiler will in fact turn it into version 2 - no performance difference whatsoever.
More importantly given we have only 3 properties it might not make a difference, but at what point do you switch from concat to builder?
At the point where you're concatenating in a loop - that's usually when the compiler can't substitute StringBuilder by itself.
The key is whether you are writing a single concatenation all in one place or accumulating it over time.
For the example you gave, there's no point in explicitly using StringBuilder. (Look at the compiled code for your first case.)
But if you are building a string eg inside a loop, use StringBuilder.
To clarify, assuming that hugeArray contains thousands of strings, code like this:
...
String result = "";
for (String s : hugeArray) {
result = result + s;
}
is very time- and memory-wasteful compared with:
...
StringBuilder sb = new StringBuilder();
for (String s : hugeArray) {
sb.append(s);
}
String result = sb.toString();
I prefer:
String.format( "{a: %s, b: %s, c: %s}", a, b, c );
...because it's short and readable.
I would not optimize this for speed unless you use it inside a loop with a very high repeat count and have measured the performance difference.
I agree, that if you have to output a lot of parameters, this form can get confusing (like one of the comments say). In this case I'd switch to a more readable form (perhaps using ToStringBuilder of apache-commons - taken from the answer of matt b) and ignore performance again.
链接地址: http://www.djcxy.com/p/24856.html上一篇: 连接字符串/字符的向量