You may use the const keyword to declare a constant. A constant is a variable that must be assigned once only when it is created. After that it is illegal to assign to a constant.
Example 5.3. Constant Example
// Declare some constants const int ANSWER = 42; const double PI = 3.142; const string[] ELEMENTS = ["Earth", "Air", "Fire", "Water"]; // These are all illegal because they attempt to write to constants ANSWER = 17; ELEMENTS.resize(5, "Duct Tape"); ELEMENTS[0] = "Muck"; // This is legal for(int i = 0; i < ELEMENTS.length(); i++) print("Element " + (i + 1) + " = " + ELEMENTS[i]); // Object references can be constant, but there is little point. You can still // call methods on the object even if they may alter its state. const Connection conn = new Connection("Data Source Name"); conn.execute("UPDATE table SET column = " + ANSWER); // You can't do this since it's a const reference conn = null;