Learn how to build a Java program that reads expressions like 3*5, 5/5*2+8/2+5 from a text file and solves them using correct operator precedence. This project involves file I/O, string parsing, handling * and / before + and -, and ensuring left-to-right evaluation for multiplication/division. Full working code for both the ExpressionSolver and the ExpressionSolverRunner is included.
The programmer will write the ExpressionSolverRunner that will use the
ExpressionSolver class to solve an integer expression provided by the
ExpressionSolver textfile. An expression will a String and it will be
comprised of number and the mathematical operators +, *, /, and -. The %
operation will not be a part of this program. In order to read an
expression, the user must read the expression from left to right performing
the multiplication and division operators before attempting the
subtraction arguments. The programmer should be careful to follow the
order of operations, or they will not get the correct answer. The
calculation is integer mathematics, so there will be no rounding but just
truncation. The programmer should take particular care when a
multiplication and a division or next to each other and make sure to do
the operations from left to right. There will be no parenthesis in the
expression.
Answer
import
java.util.*;
import
java.io.*;
public
class ExpressionSolverRunner {
public
static void main( String args[] ){
String
s1 = "Java isn't just for breakfast.";
String
s2 = "JAVA isn't just for breakfast.";
if
(s1.equals(s2))
System.out.println("The
two lines are equal.");
else
System.out.println("The
two lines are not equal.");
if
(s1.equalsIgnoreCase(s2))
System.out.println("But
the lines are equal, ignoring case.");
else
System.out.println("Lines
are not equal, even ignoring case.");
Scanner
input =new Scanner(System.in);
System.out.print
("Please enter a file name to read :");
String
filename = input.nextLine();
// //
instance object
ExpressionSolver
problem = new ExpressionSolver();
// read
file as 3*5 3-5 5/5*2+8/2+5
try {
File myObj = new File(filename);
Scanner myReader = new Scanner(myObj);
while (myReader.hasNextLine()) {
String data =
myReader.nextLine();
String words[] =
data.split(" ");
for(int i = 0; i <
words.length ; i++){
System.out.print
(problem.CalculationExpression(words[i]));
}
} // end while
myReader.close();
} catch
(FileNotFoundException e) {
System.out.println("An error
occurred.");
}
}// end
main
}// end
class
import
java.util.*;
public class ExpressionSolver
{
public
static String CalculationExpression
(String ExpressionToCalculate) {
String
expression = ExpressionToCalculate,
StringCalculation = "" , provisional;
int
PositionA = 0 , indexJ , indexK,postive,negative;
Integer
SignA , SignB , val;
for
(;ExpressionToCalculate.contains("*") ||
ExpressionToCalculate.contains("/");) {
indexK
= ExpressionToCalculate.indexOf("*");
indexJ
= ExpressionToCalculate.indexOf("/");
if
(indexK == -1) {
StringCalculation =
"/";
}
else if
(indexJ > indexK) {
StringCalculation =
"*";
}
else if
(indexJ == -1) {
StringCalculation =
"*";
}
else if
(indexK > indexJ) {
StringCalculation =
"/";
}
PositionA =
ExpressionToCalculate.indexOf(StringCalculation);
SignA = SignB = 0;
int i = PositionA;
for
( ;
i > 0 ; ) {
try {
i--;
SignA =
Integer.parseInt(ExpressionToCalculate.substring(i, PositionA));
} catch (NumberFormatException
exception ) {
break;
}
}
i = PositionA + 1;
while
(i < ExpressionToCalculate.length()) {
try {
i++;
SignB =
Integer.parseInt(ExpressionToCalculate.substring(PositionA + 1, i));
} catch (NumberFormatException
exception) {
break;
}
}
if
(StringCalculation.equals("*")) {
val = SignA * SignB;
provisional = SignA.toString() +
StringCalculation + SignB.toString();
ExpressionToCalculate =
ExpressionToCalculate.replace(provisional, val.toString());
}
else if
(StringCalculation.equals("/")) {
val = SignA / SignB;
provisional = SignA.toString() +
StringCalculation + SignB.toString();
ExpressionToCalculate =
ExpressionToCalculate.replace(provisional, val.toString());
}
}
for
( ;
ExpressionToCalculate.contains("+") ||
ExpressionToCalculate.contains("-")
; ) {
postive =
ExpressionToCalculate.indexOf("+");
negative =
ExpressionToCalculate.indexOf("-");
if
(negative == 0) {
break;
}
else if
(postive == -1) {
StringCalculation =
"-";
}
else if
(negative == -1) {
StringCalculation =
"+";
}
else if
(postive < negative) {
StringCalculation =
"+";
}
else if
(negative < postive) {
StringCalculation =
"-";
}
PositionA =
ExpressionToCalculate.indexOf(StringCalculation);
SignA = 0;
SignB = 0;
int i = PositionA;
while
(i > 0) {
try {
i--;
SignA = Integer.parseInt(ExpressionToCalculate.substring(i,
PositionA));
} catch (NumberFormatException
exception) {
break;
}
}
i = PositionA + 1;
for ( ;
i < ExpressionToCalculate.length() ; ) {
try {
i++;
SignB =
Integer.parseInt(ExpressionToCalculate.substring(PositionA + 1, i));
} catch (NumberFormatException
exception) {
break;
}
}
if
(StringCalculation.equals("+")) {
val = SignA + SignB;
provisional = SignA.toString() +
StringCalculation + SignB.toString();
ExpressionToCalculate =
ExpressionToCalculate.replace(provisional, val.toString());
}
else if
(StringCalculation.equals("-")) {
val = SignA - SignB;
provisional = SignA.toString() +
StringCalculation + SignB.toString();
ExpressionToCalculate =
ExpressionToCalculate.replace(provisional, val.toString());
}
}
return expression + " = " +
ExpressionToCalculate +" " ;
}
}
Input.txt
3*5 3-5
5/5*2+8/2+5