jsetfield

c = jcompile("Test", ["public class Test {";
                      "public int field;";
                      "public Test(int n) {";
                      "field = n;";
                      "}";
                      "}";]);
t = c.new(128);
t.field
jsetfield(t, "field", 256);
t.field

// But it is easier to use...
t.field = 512;
t.field
jremove c t;

jimport java.util.Date;

d = Date.new();
d.minutes = 3; // will call d.setMinutes(3);
jsetfield(d, "minutes", 3); // will call d.setMinutes(3);

jremove Date d;