A UML class diagram

import javax.swing.*; import java.awt.event.ActionEvent; import java.io.IOException; import java.util.EmptyStackException;

public class P2GUI extends JFrame {

// Variables private String expression;

// Creates Instance of ExpressionEval private ExpressionEval expressionEval = new ExpressionEval();

/** * Creates the GUI for the program, as well as handles Action Listeners */ private P2GUI() { // Set Title super("Three Address Generator");

// Create Panels JPanel main = new JPanel(); JPanel inputPanel = new JPanel(); JPanel constructPanel = new JPanel(); JPanel resultPanel = new JPanel();

// Set Layout main.setLayout(new BoxLayout(main, BoxLayout.Y_AXIS));

// Create Components JLabel inputLabel = new JLabel("Enter Postfix Expression"); JTextField inputTxt = new JTextField(null,20); JButton constructBtn = new JButton("Construct Tree"); JLabel resultLabel = new JLabel("Infix Expression"); JTextField resultTxt = new JTextField(null,20);

// Add Input Components inputPanel.add(inputLabel); inputPanel.add(inputTxt);

// Add Construct Components constructPanel.add(constructBtn);

// Add Result Components resultPanel.add(resultLabel); resultPanel.add(resultTxt); resultTxt.setEditable(false);

// Add Panels to main main.add(inputPanel); main.add(constructPanel); main.add(resultPanel);

// Add main to JFrame add(main);

// JFrame Settings setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE); setSize(400,145); setLocationRelativeTo(null); setResizable(false); setVisible(true);

// "Construct Tree" Button Handler constructBtn.addActionListener((ActionEvent e) -> { expression = inputTxt.getText();

try { if (expression.isEmpty()) { throw new NullPointerException(); } else { resultTxt.setText(expressionEval.evaluate(expression)); } } catch (InvalidTokenException e1) { JOptionPane.showMessageDialog(null, "Invalid Token: " + e1.getMessage(),"Error",JOptionPane.ERROR_MESSAGE); } catch (NullPointerException e2) { JOptionPane.showMessageDialog(null, "A Postfix Expression is required.","Error",JOptionPane.ERROR_MESSAGE); } catch (EmptyStackException empty) { JOptionPane.showMessageDialog(null, "Invalid Postfix Expression. Check Operators and Operands.","Error",JOptionPane.ERROR_MESSAGE); } catch (IOException e1) { JOptionPane.showMessageDialog(null, "Error Writing to File.","Error",JOptionPane.ERROR_MESSAGE); } }); }

public static void main(String[] args) { new P2GUI(); } } ----------------------------------------------------------------------------------------------------- import java.io.IOException; import java.util.EmptyStackException; import java.util.Stack;

class ExpressionEval {

// Variables private Stack expressionStack = new Stack<>(); private Node operator;

String evaluate(String expression) throws InvalidTokenException, EmptyStackException, IOException { String[] tokens = expression.split(" ");

for (String token : tokens) { // Determines patterns used to determine tokens String operandPat = "[\\d.?]+"; String operatorPat = "[*/+\\-]";

// Ensures no illegal characters are used if (!token.matches(operandPat) && !token.matches(operatorPat)) { throw new InvalidTokenException(token); }

// Pushes Operands onto Stack. Assigns children to Operators, then pushes Operators onto Stack if (token.matches(operandPat)) { expressionStack.push(new OperandNode(token)); } else if (token.matches(operatorPat)) { operator = new OperatorNode(token, expressionStack.pop(), expressionStack.pop()); expressionStack.push(operator); } }

// Creates the Assembly Code written to File operator.post();

return expressionStack.pop().inOrderWalk(); } } ------------------------------------------------------------------------------------------------------ public class InvalidTokenException extends Exception { public InvalidTokenException(String token) { super(token); } } ------------------------------------------------------------------------------- import java.io.IOException;

public interface Node { String inOrderWalk(); String postOrderWalk() throws IOException; void post() throws IOException; } ----------------------------------------------------------------------------- public class OperandNode implements Node {

private String value;

/** * Assigns values to proper variables */ OperandNode(String value) { this.value = value; }

/** * Used for creating the Infix Expression */ public String inOrderWalk() { return String.valueOf(value); }

/** * Used for creating the Postfix Expression, as well as 3-Address.txt */ public String postOrderWalk() { return String.valueOf(value); }

/** * Helper method for postOrderWalk */ public void post() {} } --------------------------------------------------------------------------------------------- import java.io.BufferedWriter; import java.io.File; import java.io.FileWriter; import java.io.IOException;

public class OperatorNode implements Node {

// Variables private String operator; private Node right, left; private static int i; // register count for 3-address code private File file = new File("3-Address.txt"); // creates 3-Address text file on users Desktop

OperatorNode(String operator, Node right, Node left) { this.operator = operator; this.right = right; this.left = left;

operatorEval(operator); }

/** * Create the Infix Expression */ public String inOrderWalk() { return "(" + left.inOrderWalk() + " " + operator + " " + right.inOrderWalk() + ")"; }

/** * Helper method for postOrderWalk */ public void post() throws IOException { i = 0; // sets count postOrderWalk(); // starts the walk }

/** * Walks tree in PostOrder, then writes each step in expression to file */ public String postOrderWalk() throws IOException { String leftValue = left.postOrderWalk(); String rightValue = right.postOrderWalk(); String opValue = operatorEval(this.operator);

String result = "R" + i++;

// Creates string with a step in the expression then writes to file String step = opValue + " " + result + " " + leftValue + " " + rightValue; writeToFile(step);

return result; }

/** * Assigns a word to each type of operator, helper method for postOrderWalk */ private String operatorEval(String operator) { String op = "";

switch (operator) { case "+": op = "Add"; break; case "-": op = "Sub"; break; case "*": op = "Mul"; break; case "/": op = "Div"; break; }

return op; }

/** * Writes a line to the 3-Address.txt file, helper method for postOrderWalk */ private void writeToFile(String step) throws IOException { BufferedWriter bw = new BufferedWriter(new FileWriter(file,true)); bw.write(step); bw.newLine(); bw.close(); } }