private void execute() {
    if (sourceFile == null) {
      printError("-i : No source file specified");
    }

    if (assembler == null || computer == null) {
      printError("-f : No format specified");
    }

    if (assembler.hasErrors()) {
      printError("Unable to execute file due to errors");
    }

    print("...preparing to execute program");

    if (trace) {
      print("...opening computer trace files");
      addTraceListeners();
    }

    computer.setExecutionSpeed(ExecutionSpeed.FULL);
    computer.setInstructions(assembler.getInstructions());

    computer.addComputerListener(
        new ComputerAdapter() {
          public void computerStarted(Computer computer) {
            print("...Execution started");
          }

          public void computerStopped(Computer computer) {
            print("...Execution complete");
          }
        });

    computer.execute();
  }