HI ALL!
As part of my Java self-study, I am trying to fulfill one of the Java beginner assignments here (very old stuff - 2001)
The problem is that I do not know how to approach this problem :( I will be grateful for any suggestions, since the solution is no longer available, only a link to zipped archives works fine.
Regards, Mary
PS. Appointment:
** "** Task 3: Assignment for topic 3, subclasses
(This is a revision of a project created by Prof. Cindy Norris of CS, Appalachian State University)
The goal of this assignment is to give you practice with subclasses in customization, where they are especially useful. You will write an interpreter for a minimal machine language - MML. General form of machine language instruction
list of instructions for shortcuts
label is the label for the string. Other instructions may “jump” to this label.
the instruction is the actual instruction. In MML, there are instructions for adding, multiplying, etc. For storing and extracting integers and for conditional branching to other labels (for example, the if statement).
register-list - a list of registers that the instruction manipulates. Registers are simple, intact, storage areas in computer memory, like variables. There are 32 registers in MML, numbered 0, 1, ..., 31.
MML has the following instructions:
L1 add r s1 s2 - add the contents of registers s1 and s2 and save the result in register r.
L1 sub r s1 s2 - subtract the contents of register s2 from the contents of s1 and save the result in register r.
L1 mul r s1 s2 . Multiply the contents of registers s1 and s2 and save the result in register r.
L1 div r s1 s2 - Separate (integer integer) the contents of register s1 with the contents of register s2 and save the result in register r.
L1 out s1 . Print the contents of register s1 in the Java console (using println).
L1 lin rx - store integer x in register r.
L1 bnz s1 L2 If the contents of register s1 is not zero, then make the statement marked as L2, the next one to execute.
We have kept a small number of different instructions so that you have less work. For example, there may be other branch instructions, a negation instruction, an introductory instruction, etc. But once you implement this little language, it will be easy for you to add additional instructions.
L1 - any identifier - in fact, any sequence of characters without spaces. Each program statement must be marked with a different identifier. Each of s1, s2 and r is an integer in the range 0..31 and refers to one of 32 registers on a machine that runs the MML language. The following is an example of an MML program for calculating factorial 6. Note that adjacent instruction fields (label, opcode, and operands) are separated by spaces.
f0 lin 20 6 f1 lin 21 1 f2 lin 22 1 f3 mul 21 21 20 f4 sub 20 20 22 f5 bnz 20 f3 f6 out 21
The program instructions are executed in order (starting from the first) if the order is not changed by executing the bnz command. Execution ends when its last instruction is executed (and does not change the order of execution).
Your translator will
- Get the name of the file containing the program from the user,
- Read the program from the file and translate it into the internal form,
- Print the program,
- Run the program and
- Print the final register value. "
Machine.java
import java.util.*; // The machine language interpreter public class Machine { // The labels in the MML program, in the order in which // they appear (are defined) in the program private Labels labels= new Labels(); // The MML program, consisting of prog.size() instructions, each // of class Instruction (or one of its subclasses) private Vector prog= new Vector(); // The registers of the MML machine private Registers registers; // The program counter; it contains the index (in prog) of // the next instruction to be executed. private int PC= 0; public static void main (String[] pars) { Machine m= new Machine(); Translator.readAndTranslate(m.labels, m.prog); System.out.println("Here is the program; it has " + m.prog.size() + " instructions."); m.print(); System.out.println(); System.out.println("Beginning program execution."); m.execute(); System.out.println("Ending program execution."); System.out.println("Values of registers at program termination:"); System.out.println(m.registers + "."); System.exit(0); } // Print the program public void print() { for (int i= 0; i != prog.size(); i++) { System.out.println((Instruction) prog.elementAt(i)); } } // Execute the program in prog, beginning at instruction 0. // Precondition: the program and its labels have been store properly. public void execute() { PC= 0; registers= new Registers(); while (PC < prog.size()) { Instruction ins= (Instruction)prog.elementAt(PC); PC= PC+1; ins.execute(this); } } // = the registers of this machine public Registers getRegisters() { return registers; } // = the labels of this machine public Labels getLabels() { return labels; } // Set the program counter to pc public void setPC(int pc) { PC= pc; } }
Translator.java
import java.io.*; import java.util.*; import javax.swing.*; // The translator of a small program. All the fields and methods are static. public class Translator { private static BufferedReader br; // Reader attached to the file chosen by the user // word + line is the part of the current line that not yet processed // word has no whitespace // If word and line are not empty, line begins with whitespace private static String line=""; private static String word=""; private static Labels labels; // The labels of the program being translated private static Vector program; // The program to be created // Obtain a file name from the user and translate the // small program in that file into lab (the labels) and // prog (the program) // return "no errors were detected" public static boolean readAndTranslate(Labels lab, Vector prog) { try { getReader(); } catch(IOException ioE) { System.out.println("Sai: IO error to start " ); return false; } labels= lab; labels.reset(); program= prog; program.removeAllElements(); try { line = br.readLine(); } catch (IOException ioE) { return false; } // Each iteration processes line and reads the next line into line while (line != null) { // Store the label in label String label= scan(); if (label.length() > 0) { Instruction ins= getInstruction(label); if ( ins != null ) { labels.addLabel(label); program.addElement(ins); } } try { line = br.readLine(); } catch (IOException ioE) { return false; } } return true; } // line should consist of an MML instruction, with its label already // removed. Translate line into an instruction with label label // and return the instruction public static Instruction getInstruction(String label) { int s1; // Possible operands of the instruction int s2; int r; int x; String L2; String ins= scan(); if (line.equals("")) return null; if (ins.equals("add")) { r= scanInt(); s1= scanInt(); s2= scanInt(); return new AddInstruction(label, r, s1, s2); } // You will have to write code here for the other instructions. return null; } // Display a JFileChooser and set br to a reader for the file chosen private static void getReader() throws IOException { JFileChooser chooser = new JFileChooser("C:\\Windows\\Desktop\\compiler\\test0.txt"); chooser.setDialogTitle("Choose the File that contains the MML program to be executed"); chooser.showOpenDialog(null); br = new BufferedReader(new FileReader(chooser.getSelectedFile())); } // Return the first word of line and remove it from line. // If there is no word, return "" public static String scan() { line= line.trim(); if (line.length() == 0) { return ""; } int i= 0; while (i < line.length() && line.charAt(i) != ' ' && line.charAt(i) != '\t') { i= i+1; } word= line.substring(0,i); line= line.substring(i); return word; } // Return the first word of line as an integer. If there is // any error, return the maximum int public static int scanInt() { String word= scan(); if (word.length() == 0) { return Integer.MAX_VALUE; } try { return Integer.parseInt(word); } catch (NumberFormatException e) { return Integer.MAX_VALUE; } } }
Labels.java
import java.util.*; // An instance contains a list of Strings, called "labels", // in the order in which they were added to the list. public class Labels { private Vector labels= new Vector(); // Constructor: an empty list of labels public Labels() { } // Add label lab to this list and return its number in the list // (the first one added is number 0) // Precondition: the list has at most 49 entries public int addLabel(String lab) { labels.addElement(lab); return labels.size()-1; } // = the number of label lab in the list // (= -1 if lab is not in the list) public int indexOf(String lab) { // invariant: lab is not in labels[0..i-1] for (int i= 0; i != labels.size(); i++) { if (lab.equals((String)(labels.elementAt(i)))) { return i; } } return -1; } // representation of this instance, "(label 0, label 1, ..., label (n-1))" public String toString() { String r= "("; // invariant: r contains the representation for labels[0..i-1] // (with the opening "(" but no closing ")") for (int i= 0; i != labels.size(); i++) { if (i == 0) { r= r + (String)(labels.elementAt(i)); } else { r= r + ", " + (String)(labels.elementAt(i)); } } r= r + ")"; return r; } // Set the number of elements in the list to 0 public void reset() { labels.removeAllElements(); } }
Registers.java
// An instance contains 31 registers and methods to access // and change them public class Registers { private int registers[]= new int[31]; // Constructor: an instance whose registers are set to 0 public Registers() { for (int i= 0; i != registers.length; i++) { registers[i]= 0; } } // = the value in register i. // Precondition: 0 <= i < 32 public int getRegister(int i) { return registers[i]; } // Set register i to v. // Precondition: 0 <= i < 32 public void setRegister(int i, int v) { registers[i]= v; } // = a representation of the registers, // "(reg 0, reg 1, ..., reg 31)" public String toString() { String r= "(" + registers[0]; // invariant: r contains the representation for registers[0..i-1] // (with the opening "(" but no closing ")") for (int i= 1; i != registers.length; i++) { r= r + ", " + registers[i]; } r= r + ")"; return r; } }
Instruction.java