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9/7: Variable Types, Arithmetic Operators, Comparison Operators • • • • Addition.java in depth Variable types & data types Input from user: how to get it Arithmetic operators Addition.java import statement class import javax.swing.JOptionPane; header method header public class Addition { public static void main ( String args[] ) declaring { variables: String firstNumber, secondNumber; Strings int number1, number2, sum; & ints 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 ); } } 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 import javax.swing.JOptionPane; public class Addition { public static void main ( String args[] ) { String firstNumber, secondNumber; initializing int number1, number2, sum; firstNumber & secondNumber 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 ); } } 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 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" ); initializing number1 & number2 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 ); } } 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 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 ); initializing sum sum = number1 + number2; JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } } Arithmetic Operators Java operator Arithmetic operator Addition + Algebraic expression Java expression f+7 f+7 Subtraction - p–c p–c Multiplication * pv p*v Division / x/y x/y Modulus % r mod s r%s 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 1st Program of the Day: pg. 58 • Pg. 58: Comparison.java – Pay attention to the comparison operators (<, >=, etc.) • Second Half: – Comparison.java in depth: – the if structure – comparison operators – assigning new values to an old variable. Part 2: Comparison Operators • Comparison.java • Using the if structure • Equality operators • Relational operators import statement Comparison.java import javax.swing.JOptionPane; class header method header public class Comparison { public static void main( String args[] ) declaring { variables: String firstNumber, secondNumber, result; Strings int number1, number2; & ints initializing firstNumber & secondNumber firstNumber = JOptionPane.showInputDialog( "Enter first int.:" ); secondNumber = JOptionPane.showInputDialog( "Enter 2nd int:" ); initializing number1 & number2 number1 = Integer.parseInt( firstNumber ); number2 = Integer.parseInt( secondNumber ); initializing result result = ""; Comparison.java (pt. 2) if ( number1 == number2 ) result = number1 + " == " + number2; if ( number1 != number2 ) result = number1 + " != " + number2; “If number1 is equal to number2, then set result to be number1 plus a double equal sign plus number2.” if ( number1 < number2 ) result = result + "\n" + number1 + " < " + number2; if ( number1 > number2 ) result = result + "\n" + number1 + " > " + number2; if ( number1 <= number2 ) result = result + "\n" + number1 + " <= " + number2; if ( number1 >= number2 ) result = result + "\n" + number1 + " >= " + number2; The if structure Use the if structure to have statements execute ONLY under certain conditions. if ( condition ) rest of statement ; Note that the if ( condition ) is not a statement by itself ( just like English ). The spacing and line structure is good practice. Comparison.java (pt. 2) if ( number1 == number2 ) result = number1 + " == " + number2; if ( number1 != number2 ) result = number1 + " != " + number2; “If number1 is less than number2, set result to be itself plus a new line escape sequence plus number1 plus a ‘less than’ sign plus number2.” if ( number1 < number2 ) result = result + "\n" + number1 + " < " + number2; if ( number1 > number2 ) result = result + "\n" + number1 + " > " + number2; if ( number1 <= number2 ) result = result + "\n" + number1 + " <= " + number2; if ( number1 >= number2 ) result = result + "\n" + number1 + " >= " + number2; Equality & Relational Operators • To compare values. • Equality operators: Equal to, not equal to • Relational operators: Greater than, less than Equality Operators English phrase Algebraic Equality Operator Java equality operator Example of Java condition x is equal to y = == x == y x is not equal to y = != x != y Relational Operators English phrase Algebraic Relational Operator Java Example of relational Java condition operator x is greater than y > > x > y x is less than y < < x < y x is greater or equal to y x is less than or equal to y > >= x >= y < <= x <= y Comparison.java (pt. 3) JOptionPane.showMessageDialog( null, result, "Comparison Results", JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); } } result, whatever it is after executing the if statements, is put in the main body of the MessageDialog box. Program of the Day • Problem 2.17 (pg. 73): write a program • Work in pairs • Use Comparison.java as a help/template in creating the program