import java.util.Map;
import java.io.IOException;
public class Controller{
 public Map<String, Instruction> cnt;

public Controller() {

cnt = new HashMap<String, Instruction>();

class ADD implements Instruction {
 public void execute(String [] args, CPUReg regFile)
  throws IOException {
    regFile.writeReg(args[1],regFile.readReg(args[2]) + regFile.readReg(args[3]));
}
}
cnt.put("ADD", new ADD());
// do that for all instructions

public void executeInstruction(String [] args, CPUReg regFile)
throws IOException {

Instruction inst = cnt.get(args[0]);
if(inst == null) throw new IOException("Cannot find instruction");

inst.execute(args, regFile);
}
}
}

^

^