java字符串反转

public static String reverseString(String x) {
if (x == null || x.length() < 2)
return x;
else
return reverseString(x.substring(1)) + x.charAt(0);
}

public static String reverse(String str){
return new StringBuilder(str).reverse().toString();
}

public static String reverse(String str){
String c ="";
for (int i = str.length() - 1; i >= 0; i--) {

c+= str.charAt(i);

}
return c;
}