java_advanced_io_demos_index 08/14/18 07:14:41 walton 1 of 1

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1 java_advanced_io_demos_index 08/14/18 07:14:41 walton 1 of 1 JAVA ADVANCED IO DEMOS Tue Aug 14 07:14:41 EDT 2018 Advanced Input/Output Demonstrations vcalc 2D Geometry Algorithms vcalc.txt vcalc.java Problem statement. JAVA solution.

2 vcalc.txt 12/29/14 05:23:47 walton 1 of 4 Simple Vector Calculator You have been asked to implement a very simple vector calculator. The tokens of its input are <separator> ::= ( ), : <end-of-line> <symbol> ::= <symbol-character> <symbol-character>* <symbol-character> ::= character other than a <separator>, single space, horizontal tab, and form feed Given this the following are particular tokens: <variable> ::= <symbol> beginning with a letter <operator> ::= one of the following symbols: + - * / ^! && ==!= < <= > >= Whitespace is ignored except for its role in separating tokens and for the <end-of-line> token. Note that operators must be delimited by whitespace or separators. <simple-statement> ::= print <symbol>* <end-of-line> println <symbol>* <end-of-line> <variable> = <expression> <end-of-line> clear <variable>* <end-of-line> <expression> ::= <boolean-expression> <scalar-expression> <vector-expression> <boolean-expression> ::= <boolean-atom>! <boolean-atom> <boolean-atom> && <boolean-atom> <boolean-atom> <boolean-atom> <scalar-atom> == <scalar-atom> <scalar-atom>!= <scalar-atom> <scalar-atom> < <scalar-atom> <scalar-atom> <= <scalar-atom> <scalar-atom> > <scalar-atom> <scalar-atom> >= <scalar-atom> Blank lines are ignored. Any line whose first nonwhitespace characters are is a comment line and is ignored. Given these tokens, the syntax accepted by the calculator is: <program> ::= <statement>* <statement> ::= <simple-statement> if <boolean-atom>: <simple-statement> <boolean-atom> ::= <variable> with boolean value true false <scalar-expression> ::= <scalar-atom> - <scalar-atom> <scalar-atom> <scalar-atom> + <scalar-atom> <scalar-atom> - <scalar-atom> <scalar-atom> * <scalar-atom> <scalar-atom> / <scalar-atom> <scalar-atom> ::= <variable> with scalar value <number>

3 vcalc.txt 12/29/14 05:23:47 walton 2 of 4 <vector-expression> ::= <vector-atom> - <vector-atom> <vector-atom> angle <vector-atom> <vector-atom> + <vector-atom> <vector-atom> - <vector-atom> <scalar-atom> * <vector-atom> <vector-atom> ^ <scalar-atom> <vector-atom> ::= <variable> with vector value ( <scalar-atom>, <scalar-atom> ) This syntax is very limited so it is easy to implement. It has the following limits/peculiarities: 1. At most one operation such as + or - can appear in a statement. 2. Only very simple conditional statements are allowed, such as if x: y = 5 + z if m: y = true if p: print Y IS y 3. Operators such as +, *,, and must be delimited by whitespace, parentheses, commas, or colons. The semantics are what you would expect given the following: 1. Variables can have boolean, scalar, or vector values, or no values. Variables with no values are only legal in print statements: see below. 2. The expression s denotes the absolute value of the scalar s. 3. The expression v denotes the length value of the vector. 4. Angles are measured in degrees. Special care is taken with angles that are multiples of 90 degrees to be sure that rotations and the angle function give exact results. 5. The expression v ^ s denotes rotation of the vector v by the scalar angle s. 6. The print and println statements print symbols separated by single spaces. But if a symbol is a variable name and the variable has a value, the value is printed instead of the symbol. The print statement ends by printing just a single space so the line may be continued, while the println statement ends by printing a line end. 7. The clear statement clears the variables listed, meaning that these variables are given no value (and therefore print as their names). If no variables are given, all variables are cleared. 8. Attempts to assign a value to a variable named any of the following is an error: Input true false if clear print println Other language special symbols can be used as variable names. Input is a program. Lines and variable names may be arbitrarily long. Input ends with an end of file.

4 vcalc.txt 12/29/14 05:23:47 walton 3 of 4 Output Output is the lines printed by print statements. Numbers should be printed using decimal notation with 14 decimal places, but with trailing 0 s stripped, and integers printed with no decimal point. Scientific notation should NOT be used. Syntax and other errors, including divide by zero and taking the angle of a zero vector, should be detected and abort execution with an error message. There is no required format for error messages, and the program will not be judged with erroneous input. Sample Input Sample vcalc Input x = 5 y = -10 z = x + y println x + y = z p1 = ( 3, 4 ) p2 = ( -7, 3 ) p = ( 1, 4 ) p12 = p2 - p1 rp12 = p12 ^ 90 y = p * rp12 y1 = p1 * rp12 y2 = p2 * rp12 println p y = y ### p1 y = y1 ### p2 y = y2 print p is x = y > y1 if x: print to the left of x = y == y1 if x: print on x = y < y1 if x: print to the right of println p1 ---> p2 Sample Output = -5 p y = -39 ### p1 y = -37 ### p2 y = -37 (1, 4) is to the right of (3, 4) ---> (-7, 3)

5 vcalc.txt 12/29/14 05:23:47 walton 4 of 4 File: vcalc.txt Author: Bob Walton <walton@seas.harvard.edu> Date: Wed Jan 23 11:22:53 EST 2013 The authors have placed this file in the public domain; they make no warranty and accept no liability for this file. RCS Info (may not be true date or author): $Author: walton $ $Date: 2013/01/23 16:23:07 $ $RCSfile: vcalc.txt,v $ $Revision: 1.11 $

6 vcalc.java 12/29/14 05:23:47 walton 1 of 10 Solution to the Simple Vector Calculator Problem File: vcalc.java Authors: Bob Walton (walton@seas.harvard.edu) Date: Mon Feb 18 06:17:03 EST 2013 The authors have placed this program in the public domain; they make no warranty and accept no liability for this program. import java.util.scanner; import java.util.regex.pattern; import java.util.hashtable; import java.text.decimalformat; public class vcalc static boolean debug = false; static void print ( String s ) System.out.print ( s ); static void println ( String s ) System.out.println ( s ); static void println ( ) System.out.println(); static void dprint ( String s ) if ( debug ) System.out.print ( s ); static void dprintln ( String s ) if ( debug ) System.out.println ( s ); Used to get the equivalent of %.14f but with trailing fraction zeros suppressed. Use decimal.format ( x ) to convert double to string. static DecimalFormat decimal = new DecimalFormat ( "0.##############" ); final static Scanner scan = new Scanner ( System.in ).usedelimiter ( "[(),: \t\f\n]+" ); Returns next token or EOL if end of line or EOF if end of file. We make EOL and EOF be printable strings as tokens are printed in many error messages. Implements one-token backup. Implements line_number. All tokens are printable Strings and none are of zero length. final static String EOL = new String ( "(END-OF-LINE)" ); final static String EOF = new String ( "(END-OF-FILE)" ); static boolean backup = false; Set backup = true to backup. static int line_number = 0; Current line number; 1, 2, 3,... static String last_token = EOL; static Pattern comment = Pattern.compile ( "\\G[ \t\f]*(.* )(?m)$" ); Skips to end of line for both comment and blank line. static Pattern end_of_line = Pattern.compile ( "\\G\n" ); Use in findwithinhorizon ( end_of_line, 1 ). static Pattern end_space = Pattern.compile ( "\\G[ \t\f]*(?m)$" ); Skips horizontal whitespace before end of line. static Pattern separator = Pattern.compile ( "\\G[ \t\f]*([(),:])" );

7 vcalc.java 12/29/14 05:23:47 walton 2 of 10 Use in findinline ( separator ). static String get_token ( ) if ( backup ) backup = false; return last_token; if ( last_token.equals ( EOL ) ) while ( true ) ++ line_number; String s = scan.findinline ( comment ); if ( scan.findwithinhorizon ( end_of_line, 1 ) == null ) break; last_token = scan.findinline ( separator ); if ( last_token!= null ) last_token = scan.match().group ( 1 ); scan.findinline ( end_space ); Get rid of any horizontal whitespace before a line feed. if ( scan.findwithinhorizon ( end_of_line, 1 )!= null ) last_token = EOL; if ( scan.hasnext() ) last_token = scan.next(); last_token = EOF; dprint ( "" + last_token + "" ); return last_token; Print error message and exit. static void error ( String message ) println ( "ERROR in line " + line_number + ":" ); println ( " " + message ); System.exit ( 1 ); Convert token to number. If this is not possible, just return null. static Double token_to_number ( String token ) try return Double.valueOf ( token ); catch ( NumberFormatException e ) return null; static boolean is_scalar ( String token ) return token_to_number ( token )!= null; static double token_to_scalar ( String token ) Double d = token_to_number ( token ); if ( d == null ) error ( "expected scalar and got " + token + " " ); return d.doublevalue(); static void check_not_eof ( String token ) if ( token == EOF )

8 vcalc.java 12/29/14 05:23:47 walton 3 of 10 error ( "unexpected end of file" ); static void skip ( String desired ) String token = get_token(); if (! token.equals ( desired ) ) error ( "expected " + desired + " but found " + token + " " ); static boolean is_variable ( String token ) return ( Character.isLetter ( token.charat ( 0 ) ) ); static void check_variable ( String token ) if (! is_variable ( token ) ) error ( " " + token + " is not a variable" ); static class Vector double x, y; Vector ( double xval, double yval ) x = xval; y = yval; public String tostring ( ) return "(" + decimal.format ( x ) + ", " + decimal.format ( y ) + ")"; static Vector negate ( Vector v ) return new Vector ( - v.x, - v.y ); static Vector add ( Vector v1, Vector v2 ) return new Vector ( v1.x + v2.x, v1.y + v2.y ); static Vector subtract ( Vector v1, Vector v2 ) return new Vector ( v1.x - v2.x, v1.y - v2.y ); static double multiply ( Vector v1, Vector v2 ) return v1.x * v2.x + v1.y * v2.y; static Vector multiply ( double s, Vector v ) return new Vector ( s * v.x, s * v.y ); static double length ( Vector v ) return Math.sqrt ( v.x * v.x + v.y * v.y ); static double angle ( Vector v ) double result; We take extra care with angles that are multiples of 90 degrees. This is only necessary if one is using exact equality with integer coordinates instead of approximate equality. if ( v.x == 0 && v.y == 0 ) error ( "angle of zero vector" ); result = Double.NaN; Needed so compiler will not think that result does not get a value. if ( v.x == 0 ) result = ( v.y > 0? +90 : -90 ); if ( v.y == 0 ) result = ( v.x > 0? 0 : +180 );

9 vcalc.java 12/29/14 05:23:47 walton 4 of 10 result = Math.atan2 ( v.y, v.x ); result *= / Math.PI; return result; static Vector rotate ( Vector v, double angle ) double sin, cos; We take extra care with angles that are multiples of 90 degrees. This is only necessary if one is using exact equality with integer coordinates instead of approximate equality. int k = (int) ( angle / 90 ); if ( angle == k * 90 ) switch ( k % 4 ) case 0: sin = 0; cos = 1; break; case +1: case -3: sin = 1; cos = 0; break; case +2: case -2: sin = 0; cos = -1; break; case +3: case -1: sin = -1; cos = 0; break; default: sin = Double.NaN; cos = Double.NaN; Needed so compiler will not think that sin and cos do not get values. angle *= Math.PI / 180; sin = Math.sin ( angle ); cos = Math.cos ( angle ); return new Vector ( cos * v.x - sin * v.y, sin * v.x + cos * v.y ); final static int BOOLEAN = 1; final static int SCALAR = 2; final static int VECTOR = 3; static class Value int type; BOOLEAN, SCALAR, or VECTOR. boolean b; Value if BOOLEAN. double s; Value if SCALAR. Vector v; Value if VECTOR. public String tostring ( ) if ( type == BOOLEAN ) return String.valueOf ( b ); if ( type == SCALAR ) return decimal.format ( s ); if ( type == VECTOR ) return v.tostring(); return new String ( "BAD OBJECT TYPE " + type ); static Hashtable<String,Value> variable_table = new Hashtable<String,Value>(); Maps variable name Strings to Values. static void require_boolean ( Value v1 ) if ( v1.type!= BOOLEAN ) error ( "operand should be boolean" ); static void require_boolean ( Value v1, Value v2 ) if ( v1.type!= BOOLEAN ) error ( "first operand should be boolean" ); if ( v2.type!= BOOLEAN ) error

10 vcalc.java 12/29/14 05:23:47 walton 5 of 10 ( "second operand should be boolean" ); error ( "second operand should be scalar" ); static void require_scalar ( Value v1 ) if ( v1.type!= SCALAR ) error ( "operand should be scalar" ); static void require_scalar ( Value v1, Value v2 ) if ( v1.type!= SCALAR ) error ( "first operand should be scalar" ); if ( v2.type!= SCALAR ) error ( "second operand should be scalar" ); static void require_vector ( Value v1 ) if ( v1.type!= VECTOR ) error ( "operand should be vector" ); static void require_vector ( Value v1, Value v2 ) if ( v1.type!= VECTOR ) error ( "first operand should be vector" ); if ( v2.type!= VECTOR ) error ( "second operand should be vector" ); static void require_scalar_vector ( Value v1, Value v2 ) if ( v1.type!= SCALAR ) error ( "first operand should be scalar" ); if ( v2.type!= VECTOR ) error ( "second operand should be vector" ); static void require_vector_scalar ( Value v1, Value v2 ) if ( v1.type!= VECTOR ) error ( "first operand should be vector" ); if ( v2.type!= SCALAR ) Require v1 to be SCALAR or VECTOR and return true if SCALAR, false if VECTOR. static boolean is_scalar ( Value v1 ) if ( v1.type == SCALAR ) return true; if ( v1.type == VECTOR ) return false; error ( "operand should be scalar or vector" ); return false; never executed Require v1 and v2 to be BOTH SCALAR or BOTH VECTOR and return true if SCALAR, false if VECTOR. static boolean is_scalar ( Value v1, Value v2 ) if ( v1.type!= v2.type ) error ( "operands should both be scalar" + " or both be vector" ); if ( v1.type == SCALAR ) return true; if ( v2.type == VECTOR ) return false; error ( "operands should be scalar or vector" ); return false; never executed Reads a constant value and returns its Value, or a variable with a value and returns a COPY of its Value. Always returns a NEW Value.

11 vcalc.java 12/29/14 05:23:47 walton 6 of 10 static Value get_value ( ) Value v = new Value(); String token = get_token(); if ( token.equals ( "(" ) ) v.type = VECTOR; token = get_token(); double x = token_to_scalar ( token ); skip ( "," ); token = get_token(); double y = token_to_scalar ( token ); skip ( ")" ); v.v = new Vector ( x, y ); if ( token.equals ( "true" ) ) v.type = BOOLEAN; v.b = true; if ( token.equals ( "false" ) ) v.type = BOOLEAN; v.b = false; if ( is_variable ( token ) ) Value v2 = variable_table.get ( token ); if ( v2 == null ) error ( " " + token + " unassigned" ); v.type = v2.type; v.b = v2.b; v.s = v2.s; v.v = v2.v; if ( is_scalar ( token ) ) v.type = SCALAR; v.s = token_to_scalar ( token ); error ( "expected true, false, " + " scalar constant, " + " vector constant, " + " or variable but got " + token + " " ); dprint ( "[" + v.tostring() + "]" ); return v; Execute clear... statement after clear token has been read and skipped. static void execute_clear ( ) boolean found = false; while ( true ) String token = get_token(); if ( token.equals ( EOL ) ) break; check_variable ( token ); variable_table.remove ( token ); found = true; if (! found ) variable_table.clear(); Execute println... statement after println token has been read and skipped, BUT do not output final space or line end. static void execute_print ( ) boolean first = true; while ( true ) String token = get_token(); if ( token.equals ( EOL ) ) break; if ( first ) first = false;

12 vcalc.java 12/29/14 05:23:47 walton 7 of 10 print ( " " ); Value v = variable_table.get ( token ); if ( v == null ) print ( token ); print ( v.tostring() ); Execute variable =... statement after variable = tokens have been read and skipped. Check variable token to be sure its a variable name. static void execute_assign ( String variable ) check_variable ( variable ); if ( variable.equals ( "true" ) variable.equals ( "false" ) ) error ( "attempt to assign a value to " + variable + " " ); String op = get_token(); Value v1 = null; This is both the first value read and the final resulting value. Read and process statement up to but not including EOL. if ( op.equals ( "-" ) ) v1 = get_value(); if ( is_scalar ( v1 ) ) v1.s = - v1.s; v1.v = negate ( v1.v ); if ( op.equals ( " " ) ) v1 = get_value(); require_scalar ( v1 ); skip ( " " ); v1.s = Math.abs ( v1.s ); if ( op.equals ( " " ) ) v1 = get_value(); require_vector ( v1 ); skip ( " " ); v1.s = length ( v1.v ); v1.type = SCALAR; if ( op.equals ( "angle" ) ) v1 = get_value(); require_vector ( v1 ); v1.s = angle ( v1.v ); v1.type = SCALAR; if ( op.equals ( "!" ) ) v1 = get_value(); require_boolean ( v1 ); v1.b =! v1.b; Case where there is either a binary operator or no operator. backup = true; v1 = get_value(); op = get_token(); if ( op.equals ( "+" ) ) if ( is_scalar ( v1, v2 ) )

13 vcalc.java 12/29/14 05:23:47 walton 8 of 10 v1.s += v2.s; v1.v = add ( v1.v, v2.v ); if ( op.equals ( "-" ) ) if ( is_scalar ( v1, v2 ) ) v1.s -= v2.s; v1.v = subtract ( v1.v, v2.v ); if ( op.equals ( "*" ) ) if ( is_scalar ( v1 ) ) if ( is_scalar ( v2 ) ) v1.s *= v2.s; v1.v = multiply ( v1.s, v2.v ); v1.type = VECTOR; require_vector ( v1, v2 ); v1.s = multiply ( v1.v, v2.v ); v1.type = SCALAR; if ( op.equals ( "/" ) ) require_scalar ( v1, v2 ); if ( v2.s == 0 ) error ( "zero divisor" ); v1.s /= v2.s; if ( op.equals ( "^" ) ) require_vector_scalar ( v1, v2 ); v1.v = rotate ( v1.v, v2.s ); if ( op.equals ( "&&" ) ) require_boolean ( v1, v2 ); v1.b = v1.b && v2.b; if ( op.equals ( " " ) ) require_boolean ( v1, v2 ); v1.b = v1.b v2.b; if ( op.equals ( "==" ) ) require_scalar ( v1, v2 ); v1.b = ( v1.s == v2.s ); v1.type = BOOLEAN; if ( op.equals ( "!=" ) ) require_scalar ( v1, v2 ); v1.b = ( v1.s!= v2.s ); v1.type = BOOLEAN; if ( op.equals ( "<" ) ) require_scalar ( v1, v2 ); v1.b = ( v1.s < v2.s ); v1.type = BOOLEAN; if ( op.equals ( "<=" ) ) require_scalar ( v1, v2 ); v1.b = ( v1.s <= v2.s );

14 vcalc.java 12/29/14 05:23:47 walton 9 of 10 v1.type = BOOLEAN; if ( op.equals ( ">" ) ) require_scalar ( v1, v2 ); v1.b = ( v1.s > v2.s ); v1.type = BOOLEAN; if ( op.equals ( ">=" ) ) require_scalar ( v1, v2 ); v1.b = ( v1.s >= v2.s ); v1.type = BOOLEAN; if (! op.equals ( EOL ) ) error ( " " + op + " unrecognized" ); backup = true; Skip statement ending EOL. skip ( EOL ); if ( token.equals ( "if" ) ) Process if statement. If condition is true, just skip past :. Other- wise skip past EOL and go to next statement. Value v = get_value(); require_boolean ( v ); skip ( ":" ); if (! v.b ) while ( true ) token = get_token(); check_not_eof ( token ); if ( token.equals ( EOL ) ) break; continue; token = get_token(); variable_table.put ( variable, v1 ); dprintln ( "ASSIGN " + v1.tostring() + " TO " + variable ); public static void main ( String[] args ) debug = ( args.length > 0 ); Loop to read and execute a statement. while ( true ) String token = get_token(); if ( token == EOF ) break; if ( token.equals ( "clear" ) ) execute_clear(); if ( token.equals ( "print" ) ) execute_print(); print ( " " ); if ( token.equals ( "println" ) ) execute_print(); println(); skip ( "=" ); execute_assign ( token );

15 vcalc.java 12/29/14 05:23:47 walton 10 of 10