Creating Calculator using Java

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How to create a calculator on your own, tailored for Java. It contains only the basic idea so actually it can also be implemented in other languages as well.

How to create a calculator on your own, tailored for Java. It contains only the basic idea so actually it can also be implemented in other languages as well.

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  • 1. OBJECT ORIENTED PROGRAMMING
    FINAL PROJECT
    Creating Simple Calculator
    Fiona Angelina
    © 2011
  • 2. Step 1: Creating the Design
  • 3. Step 2: Make Sure All Buttons is Working
    Concatting Numbers
  • 4. Simplest Way of Concatting Number
    Treat the number as a String. Cast to Double when calculating.
    Pseudocode:
    //Get text from textfield, put it into String s
    //Concat s with other number (0, 1, 2, …, 9)
    //Set textfield with s
  • 5. Simplest Way of Concatting Number
    Code might look like this:
    String s = text.getText();
    s = s.concat(“1”);
    text.setText(s);
  • 6. Step 2: Make Sure All Buttons is Working
    Clear button
  • 7. Clearing TextField
    To clear textfield, simply set it with a new value. In this case, it is “0”.
    Code might look like this:
    text.setText(“0”);
  • 8. Step 2: Make Sure All Buttons is Working
    Backspace button
  • 9. Allowing Backspace
    Use method subSequence with start index = 0 and end index = length of string – 1.
    Don’t forget to convert the resulting CharSequence to String.
    Code might look like this:
    String s = text.getText();
    CharSequence res = s.subsequence(0, s.length() – 1);
    text.setText(res.toString());
  • 10. Step 3: Operations
  • 11. Strategy To Make Operation Works
    Strategy:
    Create two variables:
    operator: to store the last operator
    operand: to store the last operand
  • 12. How Does It Work?
    1: After finished concatting number, user clicks “+”.
    This button is clicked
  • 13. How Does It Work?
    2: Identify if it is the first number that user enters or not. Assume it is the first number, simply put the operand and operator inside the variables.
    operator = “+”
    operand = 98
  • 14. How Does It Work?
    3: User concats another number, and press “*”.
    This button is clicked
  • 15. How Does It Work?
    4: Identify if it is a first operand or not. Now it is not the first operand. Therefore you have to calculate a result.
  • 16. How Does It Work
    operator = “+”
    operand = 98
    newNum = 6
    operand = 104
    CURRENT STATUS
    operator = “*”
    operand = 104
  • 17. How Does It Work?
    5: Suppose user concats another number, and this time press “=“.
    This button is clicked
  • 18. How Does It Work?
    6: When user enters “=“ instead of other kind of operators, you have to calculate the result, and reset all the variables.
  • 19. How Does It Work?
    operator = “*”
    operand = 104
    newNum = 3
    Output the result to textfield
    operand = 312
    CURRENT STATUS
    operand = null
    operator = null
  • 20. Step 4: Playing with Memory
    Strategy:
    Create 1 null variable to represent the memory.
    M+ & M- : identify if it is the first memory. If it is, store the current value. If not, increment/decrement with the previous value.
    MC : set the memory to null.
    MR : set textfield with value inside memory.