指定某个元素和某个元素互换

package com.test;

public class TestString {

public static void main(String[] args) {
String s = "Hello";
s = reverse(s, 2, 4);
System.out.println(s);
}

public static String reverse(String s, int f, int t) {
char[] c = new char[s.length()];
for (int i = 0; i < s.length(); i++) {
if (f - 1 == i || i == t - 1) {
c[i] = s.charAt(t - (2 - f) - i);
} else {
c[i] = s.charAt(i);
}
}
return String.valueOf(c);
}
}