1/28: Inputs, Variable Types, etc.

• Addition.java in depth

• Variable types & data types

• Input from user: how to get it

• Arithmetic operators

Addition.java//Fig. 2.9: Addition.java//An addition program

//Java extension packagesimport javax.swing.JOptionPane; //import class JOptionPane

public class Addition {

//main method begins execution of Java application public static void main ( String args[] ) { String firstNumber; // first String entered by user String secondNumber; // second String entered by user int number1; // first number to add

int number 2; // second number to add int sum; // sum of number1 & number2

//read in first number from user as a String firstNumber = JOptionPane.showInputDialog

( "Enter first integer" );

import statement

classheader

methodheader

declaring variables: Strings& ints

Addition.java //read in second number from user as a String secondNumber = JOptionPane.showInputDialog

( “Enter second integer" );

//convert numbers from type String to type int number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber );

//add the numbers, assign the value to sum sum = number1 + number2;

//display the results JOptionPane.showMessageDialog ( null, “The sum is " + sum,

"Results", JOptionPane.PLAIN_MESSAGE );

System.exit ( 0 ); //terminate the application if no errors

} //end method main} //end class Addition

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.

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

Addition.java//Fig. 2.9: Addition.java//An addition program

//Java extension packagesimport javax.swing.JOptionPane; //import class JOptionPane

public class Addition {

//main method begins execution of Java application public static void main ( String args[] ) { String firstNumber; // first String entered by user String secondNumber; // second String entered by user int number1; // first number to add

int number 2; // second number to add int sum; // sum of number1 & number2

//read in first number from user as a String firstNumber = JOptionPane.showInputDialog

( "Enter first integer" );

initializing firstNumber

Addition.java //read in second number from user as a String secondNumber = JOptionPane.showInputDialog

( “Enter second integer" );

//convert numbers from type String to type int number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber );

//add the numbers, assign the value to sum sum = number1 + number2;

//display the results JOptionPane.showMessageDialog ( null, “The sum is " + sum,

"Results", JOptionPane.PLAIN_MESSAGE );

System.exit ( 0 ); //terminate the application if no errors

} //end method main} //end class Addition

initializing secondNumber

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.

Addition.java //read in second number from user as a String secondNumber = JOptionPane.showInputDialog

( “Enter second integer" );

//convert numbers from type String to type int number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber );

//add the numbers, assign the value to sum sum = number1 + number2;

//display the results JOptionPane.showMessageDialog ( null, “The sum is " + sum,

"Results", JOptionPane.PLAIN_MESSAGE );

System.exit ( 0 ); //terminate the application if no errors

} //end method main} //end class Addition

initializing number1 &number2

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.

Addition.java //read in second number from user as a String secondNumber = JOptionPane.showInputDialog

( “Enter second integer" );

//convert numbers from type String to type int number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber );

//add the numbers, assign the value to sum sum = number1 + number2;

//display the results JOptionPane.showMessageDialog ( null, “The sum is " + sum,

"Results", JOptionPane.PLAIN_MESSAGE );

System.exit ( 0 ); //terminate the application if no errors

} //end method main} //end class Addition

initializing sum

Arithmetic Operators

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 ) = ?

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

Program of the Day: pg. 81

• Pg. 81: 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.