Big Java Late Objects
Big Java Late Objects
2nd Edition
ISBN: 9781119330455
Author: Horstmann
Publisher: WILEY
Question
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Chapter 13, Problem 10PP
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”.
    • Define the constructor “Constant()”.
      • Set the value of “number”.
    • Define the method “value()”.
      • Return the value of “number”.

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”.

Filename: “Expression.java”

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

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

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.

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.

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.

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.

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”.
      • Prompt the user to enter the value for “x”.
      • Get the value of expression “input” to “value”.
      • New line
      • Print “value”.

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