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Exploring Java Variable Types and User Input with Arithmetic Operations

DESCRIPTION

This guide delves into Java programming, specifically focusing on variable types like Strings and integers, and how to read user input using `JOptionPane`. It provides a breakdown of an example program that takes two numbers from the user, converts them from String to int, performs an addition operation, and then displays the result in a dialog box. Additionally, it covers the order of arithmetic operations in Java, offering insights for both beginners and intermediate programmers aiming to enhance their coding skills.

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Exploring Java Variable Types and User Input with Arithmetic Operations

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Presentation Transcript

  1. 7/6: Inputs, Variable Types, etc. • Addition.java in depth • Variable Types & data types • Input from user: how to get it • Arithmetic operators

  2. import statement classheader method header declaring variables: Strings& ints Addition.java import javax.swing.JOptionPane; public class Addition { public static void main ( String args[] ) { String firstNumber, secondNumber; int number1, number2, sum; firstNumber = JOptionPane.showInputDialog ( "Enter a number" ); secondNumber = JOptionPane.showInputDialog ( "And another" ); number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); sum = number1 + number2; JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } }

  3. Variables & Data Types • String – a series of characters. • EX: Ann , 1450 , var30 , g , YES • to declare a String variable, put the variable type String before the name of the variable. String firstNumber ; • to declare more than one String variable at the same time, separate the variable names with commas.String firstNumber , secondNumber ; • A declaration is a statement – must end with a semicolon.

  4. Variables & Data Types • int – an integer-type number. • EX: 45 , -1001 , 3 , 58692 • to declare an int variable, put the variable type int before the name of the variable. int number1 ; • to declare more than one int variable at the same time, separate the variable names with commas. int number1 , number2 ; • other number formats: float , double , long , short

  5. initializing firstNumber &secondNumber Addition.java import javax.swing.JOptionPane; public class Addition { public static void main ( String args[] ) { String firstNumber, secondNumber; int number1, number2, sum; firstNumber = JOptionPane.showInputDialog ( "Enter a number" ); secondNumber = JOptionPane.showInputDialog ( "And another" ); number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); sum = number1 + number2; JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } }

  6. Inputs: How we did it. • We initialized (gave an initial value to) firstNumber & secondNumber by the lines firstNumber = JOptionPane.showInputDialog ( "Enter a number" ); secondNumber = JOptionPane.showInputDialog ( "And another" ); • JOptionPane.showInputDialog panes accept String type inputs. Even if it looks like a number, Java sees it as a String.

  7. initializing number1 &number2 Addition.java import javax.swing.JOptionPane; public class Addition { public static void main ( String args[] ) { String firstNumber, secondNumber; int number1, number2, sum; firstNumber = JOptionPane.showInputDialog ( "Enter a number" ); secondNumber = JOptionPane.showInputDialog ( "And another" ); number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); sum = number1 + number2; JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } }

  8. Inputs: How we did it. • We then initialized (gave an initial value to) number1 & number2 by the lines number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); • These lines convert the String values of firstNumber and secondNumber into int values and store them as number1 and number2.

  9. initializing sum Addition.java import javax.swing.JOptionPane; public class Addition { public static void main ( String args[] ) { String firstNumber, secondNumber; int number1, number2, sum; firstNumber = JOptionPane.showInputDialog ( "Enter a number" ); secondNumber = JOptionPane.showInputDialog ( "And another" ); number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); sum = number1 + number2; JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } }

  10. Arithmetic Operators

  11. Order of Operation • Just like algebra • inside parentheses first • multiplication, division, & modulus next • addition & subtraction last • left to right • EX: 2 * 4 + 3 % 2 - (4 / 2 + 5 ) = ?

  12. Order of Operation Example • 2 * 4 + 3 % 2 - (4 / 2 + 5 ) = ? • 2 * 4 + 3 % 2 - ( 2 + 5 ) = ? • 2 * 4 + 3 % 2 - ( 2+ 5 ) = ? • 2 * 4 + 3 % 2 - ( 7 ) = ? • 2 * 4 + 3 % 2 - ( 7 ) = ? • 8 + 3 % 2 - ( 7 ) = ? • 8 + 3 % 2 - ( 7 ) = ? • 8 + 1 - ( 7 ) = ? • 8 + 1 - 7 = 2

  13. Program of the Day: pg. 58 • Pg. 58: Comparison.java • Pay attention to the comparison operators (<, >=, etc.) • Next time: • Comparison.java in depth: • the if structure • comparison operators • assigning new values to an old variable.

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