Chapter 13, Problem 11PP

Program Plan Intro

Evaluation of Expression

Program plan:

Filename: “Constant.java”

This program file is used to define a class “Constant”. In the code,

• Define a class “Constant”.
  • Declare an integer “number”.
  • Define the constructor “Constant()”.
    • Set the value of “number”.
  • Define the method “value()”.
    • Return the value of “number”.
  • Define the method “toString()”.
    • Return the value of “number” as a string.

Filename: “Variable.java”

This program file is used to define a class “Variable”. In the code,

• Define a class “Variable”.
  • Define a variable “letter”.
  • Define the constructor “Variable ()”.
    • If the “letter” is not equal to “x”,
      • Throw an exception.
    • Set the letter.
  • Define the method “value()”.
    • Return the value of “x”.
  • Define the method “toString()”.
    • Return the value of “letter”.

Filename: “Expression.java”

This program file is used to define an interface “Expression”. In the code,

• Define an interface “Expression”.
  • Declare the method “value()” with argument “x”.
  • Declare a method “toString()”.

Filename: “Difference.java”

This program file is used to define a class “Difference”. In the code,

• Define a class “Difference”.
  • Define the class members “leftOp” and “rightOp”.
  • Define the constructor “Difference ()”.
    • Set the value of class members.
  • Define the method “value()” to calculate the difference of two expression.
    • Return the difference.
  • Define the method “toString()”.
    • Return the expression in string format.

Filename: “Product.java”

This program file is used to define a class “Product”. In the code,

• Define a class “Product”.
  • Define the class members “leftOp” and “rightOp”.
  • Define the constructor “Product()”.
    • Set the value of class members.
  • Define the method “value()” to calculate the product of two expression.
    • Return the product.
  • Define the method “toString()”.
    • Return the expression in string format.

Filename: “Quotient.java”

This program file is used to define a class “Quotient”. In the code,

• Define a class “Quotient”.
  • Define the class members “leftOp” and “rightOp”.
  • Define the constructor “Quotient()”.
    • Set the value of class members.
  • Define the method “value()” to calculate the quotient of two expression.
    • Return the quotient.
  • Define the method “toString()”.
    • Return the expression in string format.

Filename: “Sum.java”

This program file is used to define a class “Sum”. In the code,

• Define a class “Sum”.
  • Define the class members “leftOp” and “rightOp”.
  • Define the constructor “Sum()”.
    • Set the value of class members.
  • Define the method “value()” to calculate the sum of two expression.
    • Return the sum.
  • Define the method “toString()”.
    • Return the expression in string format.

Filename: “ExpressionTokenizer.java”

This program file is used to define a class “ExpressionTokenizer”. In the code,

• Define a class “ExpressionTokenizer”.
  • Define the class members “input”, “start” and “end”.
  • Define the constructor “ExpressionTokenizer()”.
    • Set the values of “input”, “start”, “end” and find the first token using “nextToken()”.
  • Define the method “peekToken()”.
    • If the “start” is greater than “input.length()”.
      • Return “null”.
        • Else,
        • • Return the substring.
  • Define the method “nextToken()”.
    • Call the method “peekToken()” to get the token.
    • Assign the value of “end” to “start”.
    • If the value of “start” is greater than or equal to length of the input,
      • Return the value of “r”.
        • If the character at “start” is a digit,
        • • Set “end” equal to “start+1”,
          • Iterate a “while” loop,
            • Increment the “end” by 1.
              • Set the value of “end”.
        • Return the value of “r”.

Filename: “Evaluator.java”

This program file is used to define a class “Evaluator”. In the code,

• Define a class “Evaluator”.
  • Define the class members “tokenizer” which is an object of class “ExpressionTokenizer”.
  • Define the constructor “Evaluator()”.
    • Define “tokenizer”.
  • Define the method “getExpressionValue()”.
    • Get terms using “getTermValue()” to “value”.
    • Define a Boolean value “done” and assign “false” to it.
    • While “true”,
      • Call “peekToken()” to get the token and assign to “next”.
      • If the value of “next” is “+” or “-”.
        • Get the next token using “nextToken()”.
        • Get next term to “value2”.
        • If the “next” is “+”,
        • • Calculate the sum of “value” and “value2” and assign to “value”.
        • Else,
        • • Calculate the difference of “value” and “value2” and assign to “value”.
      • Else,
        • Set “done” equal to “true”.
        • • • Return “value”.
  • Define the method “getTermValue()”.
    • Get factors using “getFactorValue()” to “value”.
    • Define a Boolean value “done” and assign “false” to it.
    • While “true”,
      • Call “peekToken()” to get the token and assign to “next”.
      • If the value of “next” is “*” or “/”.
        • Get the next token using “nextToken()”.
        • Get next factor to “value2”.
        • If the “next” is “*”,
        • • Calculate the Product of “value” and “value2” and assign to “value”.
        • Else,
        • • Calculate the Quotient of “value” and “value2” and assign to “value”.
      • Else,
        • Set “done” equal to “true”.
        • • • Return “value”.
  • Define the method “getFactorValue()”.
    • Declare “value”.
    • Call “peekToken()” to get the token and assign to “next”.
    • If the value of “next” is “(”.
      • Get the next token using “nextToken()”.
      • Discard “(” using “nextToken()”.
      • Get next expression to “value”.
      • Discard “)” using “nextToken()”.
        • • • Else,
              • If the “next” is “x”,
                • Get the variable “x” to “value”.
              • Else,
                • Get the next token to “value”.
            • Return “value”.

Filename: “ExpressionCalculator.java”

This program file is used to define a class “ExpressionCalculator”. In the code,

• Define a class “ExpressionCalculator”.
  • Define the method “main()”.
    • Define the object “in” of “Scanner”.
    • Prompt the user to enter the expression.
    • Read the lines using “nextLine()”.
    • Evaluate the expression “input”.
    • Call the method “getExprssionValue()” and save to “expr”.
    • Print “expr”.
    • Prompt the user to enter the value for “x”.
    • Scan for the value of “x”.
    • Call the method “value()” on “x” and save the result to “value”.
    • Print “value”.