java，怎样在String中每一个字符的前面插入一个字符，效率最高？

Question

例如 String str = "abcdefg";变成 str = "1a1b1c1d1e1f1g";

Answer 1

Answer 2

split分割,然后用Stringbuilder或者Stringbuffer

Answer 3

String str = "abcdefg";

str = 1 + str;

编译器会在编译的时候优化成StringBuffer