
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”.
- Define the constructor “Constant()”.
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.
- If the “letter” is not equal to “x”,
- 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.
- Return “null”.
- If the “start” is greater than “input.length()”.
- 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”.
- Increment the “end” by 1.
- Return the value of “r”.
- 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”.
- If the “next” is “x”,
- Return “value”.
- Else,
-
-
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”.
- Define the method “main()”.

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