我怎样才能在java中做得更快呢？复制长字符串的字符

String longString = "This is a long string";
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append(longString);
String copiedString = stringBuilder.toString();

String longString = "This is a long string";
char[] charArray = longString.toCharArray();
char[] copiedArray = new char[charArray.length];
System.arraycopy(charArray, 0, copiedArray, 0, charArray.length);
String copiedString = new String(copiedArray);

String longString = "This is a long string";
String copiedString = longString.substring(0);