The char or int datatypes do not have their values stored as objects. When you change the value of a char inside a char[] array, that value is directly changed in ram.

This will leave the "hello" in ram (subject to GC):

  String x = "hello"
  x = null;

This will clear the "hello" from ram:

  char[] x = new char[]{'h','e','l','l','o'};
  x[0] = '0'; x[1] = '0'; ...

This will leave the "hello" in ram (subject to GC):

  char[] x = new char[]{'h','e','l','l','o'};
  x = null;