Expression Class

2015-01-13

azim58 - Expression Class

import java.util.*;

public class Expression



/*





* Strings used for storing expression.


*/


String s, x;








/*





* Term evaluator for number literals.


*/


double term(){


double ans = 0;


StringBuffer temp = new StringBuffer();


while( s.length() > 0 && Character.isDigit( s.charAt( 0 ) ) ){


temp.append(Integer.parseInt( "" + s.charAt( 0 ) ));


s = s.substring( 1 );

if( s.length() > 0 && s.charAt( 0 ) == '.' )



temp.append( '.' );


s = s.substring( 1 );


while( s.length() > 0 && Character.isDigit( s.charAt( 0 ) ) ){


temp.append(Integer.parseInt( "" + s.charAt( 0 ) ));


s = s.substring( 1 );

}
if( s.length() > 0 && (s.charAt(0) == 'e' || s.charAt(0) == 'E') )



temp.append( 'e' );


s = s.substring( 1 );


temp.append( s.charAt( 0 ) );


s = s.substring( 1 );


while( s.length() > 0 && Character.isDigit( s.charAt( 0 ) ) ){


temp.append(Integer.parseInt( "" + s.charAt( 0 ) ));


s = s.substring( 1 );

}
ans = Double.valueOf( temp.toString() ).doubleValue();
return ans;
}

/*

Parentheses solver.
/

double paren()



double ans;


if( s.charAt( 0 ) == '(' ){


s = s.substring( 1 );


ans = add();


s = s.substring( 1 );

else



ans = term();

return ans;
}

/*

Exponentiation solver.
/

double exp()



boolean neg = false;


if( s.charAt( 0 ) == '-' ){


neg = true;


s = s.substring( 1 );

double ans = paren();
while( s.length() > 0 )



if( s.charAt( 0 ) == '^' ){


s = s.substring( 1 );


boolean expNeg = false;


if( s.charAt( 0 ) == '-' ){


expNeg = true;


s = s.substring( 1 );

double e = paren();
if( ans < 0 )

 if it's negative


double x = 1;


if( Math.ceil(e) == e ){ only raise to an integer


if( expNeg )


e *= -1;


if( e == 0 )


ans = 1;


else if( e > 0 )


for( int i = 0; i < e; i++ )


x *= ans;


else


for( int i = 0; i < -e; i++ )


x /= ans;


ans = x;

else



ans = Math.log(-1); // otherwise make it NaN

}
else if( expNeg )
ans = Math.exp( -e*Math.log( ans ) );
else
ans = Math.exp( e*Math.log( ans ) );
} else
break;
}
if( neg )
ans *= -1;
return ans;
}

/*

Trigonometric function solver.
/

double trig()



double ans = 0;


boolean found = false;


if( s.indexOf( "sin" ) == 0 ){


s = s.substring( 3 );


ans = Math.sin( trig() );


found = true;

else if( s.indexOf( "cos" ) == 0 )



s = s.substring( 3 );


ans = Math.cos( trig() );


found = true;

else if( s.indexOf( "tan" ) == 0 )



s = s.substring( 3 );


ans = Math.tan( trig() );


found = true;

if( !found )



ans = exp();

return ans;
}

/*

Multiplication, division expression solver.
/

double mul()



double ans = trig();


if( s.length() > 0 ){


while( s.length() > 0 ){


if( s.charAt( 0 ) == '*' ){


s = s.substring( 1 );


ans *= trig();

else if( s.charAt( 0 ) == '/' )



s = s.substring( 1 );


ans /= trig();

else break;
}
}
return ans;
}

/*

Addition, subtraction expression solver.
/

double add()



double ans = mul();


while( s.length() > 0 ){


if( s.charAt( 0 ) == '+' ){


s = s.substring( 1 );


ans += mul();

else if( s.charAt( 0 ) == '-' )



s = s.substring( 1 );


ans -= mul();

else



break;

}
return ans;
}

/*

Public access method to evaluate this expression.
/

public double evaluate()



s = x.intern();


double last = add();


return last;

Creates new Expression.
/

public Expression( String s )



// remove white space, assume only spaces or tabs


StringBuffer b = new StringBuffer();


StringTokenizer t = new StringTokenizer( s, " " );


while( t.hasMoreElements() )


b.append( t.nextToken() );


t = new StringTokenizer( b.toString(), "\t" );


b = new StringBuffer();


while( t.hasMoreElements() )


b.append( t.nextToken() );








x = b.toString();

The String value of this Expression.
/

public String toString()



return x.intern();

Test our Expression class by evaluating the command-line
argument and then returning.
/

public static void main( String[] args )



Expression e = new Expression( args[0] );


System.out.println( e + " = " + e.evaluate() );

}