Extra Credit Lab. Your job is to catch any syntax errors a user might make. Two examples follow. In the panel on the left the user has used

Transcription

1 Extra Credit Lab The object of this lab is to write an applet that will take a string and check to see that it is a well defined polynomial in x. A polynomial in x, recall, is an expression of the form x + 30x 45.2x When this is entered in the computer the carat has to be used for exponentiation and multiplication denoted by an asterisk. The polynomial above would be entered as * x^ * x^ * x^ 7 The applet to be written will appear like the panel on the left when first opened. Then, assuming the expression has been entered correctly the output will look like the panel on the right. Technically, the string entered has blank spaces added before and after each operator (+, -, *) and before and after any parenthesis, division sign (/). The resulting string is then tokenized to produce the tokens in the top panel on the right. Your job is to catch any syntax errors a user might make. Two examples follow. In the panel on the left the user has used

2 parenthesis. For the sake of simplicity, we shall not allow any parenthesis in our expressions. In the second panel the user pressed the enter key before entering any symbols. This gives a null input error. The general idea behind what "correct syntax" means is that x 3.2* x 4^ x + 5.4^5 between consecutive plus or minus signs there will be or or or one number one variable x one number, a * sign, followed by an x one number, a * sign, followed by an x, followed by a ^, followed by a positive integer The specific syntax rules are that the expression: is to contain no parenthesis is to have exactly one variable, called x

3 may not contain products of two or more numbers, such as 3*4 may not contain products of two or more variables, such as x*x may not contain two consecutive operators (the operators are: +, -, and * ) is to have positive integral exponents is to inform the user of null input is not to have any division signs, / may not end in a +, -, or * sign may only have the variable x come before a carat, ^ In addition you must check that each token must be a number or a positive integer or a 0, or the variable x, or an operator This lab is due Friday, March 16, at 5:30 pm /////////////////////////////////////////////////////////////////////// ////////////////////////////////////////////////////////////////////// The following is an outline of the program I wrote to do the parsing. I have left some of the code: The material dealing with getting started and some of the trickier stuff. Of course, you do not have to use it. import javax.swing.*; import java.awt.*; import java.awt.event.*; import java.util.*; public class Parse extends JApplet implements ActionListener private JLabel poly; private JTextField textfield; private JTextArea textarea; private GridLayout grid; int M; public void init() Container c = getcontentpane(); grid = new GridLayout(3,1); c.setlayout(grid); textarea = new JTextArea(10,1); textarea.setforeground(color.red); textarea.setfont( new Font("Helevetica", Font.BOLD, 12)); textarea.settext("enter input in the field below"); textarea.seteditable(false); c.add(textarea); poly = new JLabel("Enter polynomial below:"); c.add(poly); textfield = new JTextField(10);

4 textfield.setfont( new Font("Courier", Font.BOLD, 14)); textfield.setforeground(color.black); textfield.addactionlistener(this); c.add(textfield); setsize(340, 500); // end init() public void actionperformed(actionevent e) String input = textfield.gettext(); String input2 = add_blanks(input); M = Tokenize(input2).length; String itk[] = new String[M]; itk = Tokenize(input2); textarea.settext(""); String tokenlist = "number of tokens = " + M + "\n"; for (int i = 0; i < M; i++) tokenlist += itk[i]+ " "; if (i%10 == 9) tokenlist += "\n"; textarea.settext(tokenlist); try check_nullstring(m); check_parenthesis(itk); check_division(itk); check_operators(itk); check_exponent(itk); if (M >= 1) check_tail(itk[m-1]); check_multiplication(itk); check_overall(itk); check_consecutivex(itk); check_consecutivenumbers(itk); catch(nullstringexception nse) String G; G = "Input Error: Null string input"; tokenlist += "\n\n" +G; textarea.settext(tokenlist); catch(parenthesisexception pe) String J; J = "Input Error: your expression \n " + " " +input +

5 "\n contains a parenthesis"; tokenlist += "\n\n" +J; textarea.settext(tokenlist); catch(divisionexception de) catch(operatorexception oe) catch(positiveintegerexception pie) catch(tailexception te) catch(multiplicationexception me) catch(overallexception ove) catch(consecutivexexception cxe) catch(consecutivenumbersexception cne) // end actionperformed(actionevent e) ////////////////// add_blanks and Tokenize////////////////////// public String add_blanks(string st) String t = ""; for (int i = 0; i< st.length(); i++) if ( isoperator(st.charat(i)) ( st.charat(i) == '(' ) ( st.charat(i) == ')' )

6 (st.charat(i) == '/') ) t += " " + st.charat(i) + " "; else t += st.charat(i); return t; // end add_blanks(string st) public String[] Tokenize(String s) StringTokenizer tokens = new StringTokenizer(s); int N = tokens.counttokens(); String tk[] = new String[N]; for (int i = 0; i < N; i++) tk[i] = tokens.nexttoken(); return tk; ///////////////// boolean operators/////////////////////////// public boolean isoperator(char ch) boolean isoperator = false; if ( (ch == '^' ) ( ch == '+') ( ch == '-') ( ch == '*') ) isoperator = true; return isoperator; // end isoperator(char ch) public boolean isoperator(string ch) boolean isoperator = false; return isoperator; //end isoperator(string ch) public boolean isvariable(string s) // end isvariable() public boolean ispositiveinteger(string st) boolean test = true;

7 int m = st.length(); if (!( Character.isDigit(st.charAt(0)) && ( st.charat(0)!= '0' ) ) ) test = false; for (int i = 1; i <st.length(); i++) if (!Character.isDigit(st.charAt(i))) test = false; return test; // end ispositiveinteger() public boolean iszero(string st) boolean test = false; if (st.equals("0")) test = true; return test; public boolean isnumber(string st) boolean test = true; int decimalcount = 0; for(int i = 0 ; i < st.length(); i++) if (st.charat(i) == '.') decimalcount +=1; if (decimalcount > 1 decimalcount <1) test = false; if (decimalcount == 1) for (int i = 0; i < st.length(); i++) if (! (Character.isDigit(st.charAt(i)) (st.charat(i)=='.')) ) test = false; return test; // In general, a "number" can be a positive integer,a double or //the integer 0 //////////////////various check_whatever /////// public void check_parenthesis(string[] st) throws ParenthesisException boolean test = false;

8 String que = ""; for (int m = 0; m < st.length; m++) que += st[m]; for (int i = 0; i <st.length; i++) if( (st[i].equals(")") st[i].equals("(")) ) test = true; if (test) throw new ParenthesisException(); // end check_parenthesis() public void check_division(string[] st) throws DivisionException boolean test = false; if (test) throw new DivisionException(); // end check_division() public void check_operators(string[] st) throws OperatorException // end check_operators() public boolean check_exponent(string[] st) throws PositiveIntegerException if(!test ) throw new PositiveIntegerException(); return test; // end check_exponent() public void check_tail(string st) throws TailException if (test) throw new TailException(); // end check_tail() public void check_multiplication(string[] st) throws MultiplicationException

9 if (test) throw new MultiplicationException(); // end check_multiplication() public String check_overall(string[] st) throws OverallException boolean test = true; String out = ""; +i +"\n"; for (int i = 0; i < st.length; i++) String a = st[i]; if (!( isoperator(a) ispositiveinteger(a) isvariable(a) isnumber(a) iszero(a)) ) //out += "test is being set false for i = " test = false; if (!test) throw new OverallException(); return out; // end check_overall() public void check_nullstring(int n) throws NullStringException boolean test = false; if ( n == 0) test = true; if (test) throw new NullStringException (); // end check_nullstring() public void check_consecutivex(string[] st) throws ConsecutiveXException if (test) throw new ConsecutiveXException(); // end check_consecutivex(string[], st) public void check_consecutivenumbers(string[] st) throws ConsecutiveNumbersException boolean test = false;

10 if (test) throw new ConsecutiveNumbersException () ; // end check_consecutivenumbers() // class Parse class ParenthesisException extends Exception class DivisionException extends Exception class OperatorException extends Exception class PositiveIntegerException extends Exception class TailException extends Exception class MultiplicationException extends Exception class OverallException extends Exception class NullStringException extends Exception class ConsecutiveXException extends Exception class ConsecutiveNumbersException extends Exception