String Compare StringBuilder

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Intro String Compare StringBuilder

這篇介紹String Compare StringBuilder.

String優化

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在JDK5對String進行優化，String相加優化成StringBuilder的append

String a = "a";
String c = a + "b";

優化成

String c = new StringBuilder().append(a).append("b").toString();

在優化後，何時不能用String相加?

String s = "";
for (int i = 0; i <= 100000000; i++) {
	s += String.valueOf(i);
} 
會等於
for (int i = 0; i <= 100000000; i++) {
	StringBuilder s = new StringBuilder().append(String.valueOf(i));
}

實際上應使用
StringBuilder s = new StringBuilder();
for (int i = 0; i <= 100000000; i++) {
	s.append(String.valueOf(i));
}

兩者平均差距會在400多倍左右。