Chapter 9, Problem 7PP

Calculator program

Program Plan:

Filename: “Calculator.java”

• Import the required packages.
• Declare the class “Calculator”.
  • Declare the required variables.
  • Define the “init” method.
    • Declare the required variables for “JFrame”.
    • Create an object for “Container” class.
    • Create the objects for “JPanel”.
    • Create a label.
    • Create a text field.
    • Add the labels on the window.
    • Create a label.
    • Create a text field.
    • Add the labels on the window.
    • Create the buttons.
    • Add the action to these buttons.
    • Add the action to the buttons.
    • Add the buttons on the window.
    • Add the labels.
    • Set the layout.
    • Add the labels on the window.
    • Add the buttons on the window screen.
    • Add the label on the window screen.
  • Declare the “actionPerformed” method.
    • Declare the string variable.
    • In the “try” block,
      • Check the action command is equal to “Update”, call the “doCalculation” method otherwise set the text “Reset” and call the “reset” method.
      • Set the string value into “resultString” variable.
      • If the “resultString” length is greater than 15, divide the string and assign the value to the variable.
      • Set the text.
        • In the “catch” block, “UnknownOpException” exception is thrown.
        • Another “catch” block thrown “DivideByZeroException” exception.
  • Define the “reset” method.
    • Set the value as “0.0”.
  • Define the “doCalculation” method.
    • Declare the required variables.
    • Get the character position and assign it into the variable.
    • Get the substring and assign it into the variable.
    • Convert the value into double and assign it into the variable.
    • Call the method “evaluate”.
  • Define the “evaluate” method.
    • Declare the variable.
    • The “switch-case” is used to do the arithmetic operation.
    • Return the result.