package algs12;
import stdlib.*;
import java.lang.reflect.Field;
/* ***********************************************************************
 *  Compilation:  javac MutableString.java
 *  Execution:    java MutableString
 *
 *  Shows that Strings are mutable if you allow reflection.
 *
 *************************************************************************/

public class XMutableString {

  public static void main(String[] argv) {
    String s = "Immutable";
    String t = "Notreally";

    mutate(s, t);
    StdOut.println(t);

    // strings are interned so this doesn't print "Immutable"
    StdOut.println("Immutable");
  }

  // change the first min(|s|, |t|) characters of s to t
  public static void mutate(String s, String t) {
    try {
      Field val = String.class.getDeclaredField("value");
      Field off = String.class.getDeclaredField("offset");
      val.setAccessible(true);
      off.setAccessible(true);
      int offset   = off.getInt(s);
      char[] value = (char[]) val.get(s);
      for (int i = 0; i < Math.min(s.length(), t.length()); i++)
        value[offset + i] = t.charAt(i);
    }
    catch (Exception e) { e.printStackTrace(); }
  }

}