public class MultiplyExpression extends BinaryExpression {    int op;     // ID    Expression left;   // LHS expression    Expression right;   // RHS expression    Type type;     // Type of this expression    Annotation ann;   // Embedded Annotation (default: null)    void code() {     // Convert AST to backend-IR or bytecodes      if (ann) ann.execute();   // call-back for metacomputation      left.code();   // generate code for LHS      right.code();   // generate code for RHS      add(op);   // generate code for “operator”    } … }