7/19: Primitives, the for loop Primitive data types –why we mention them Return to counter-controlled repetition

Primitives: why we mention them recall Average2.java (p. 132) program: average = ( double ) total / gradeCounter ; cast operators are used to explicitly promote (or change) one primitive type to another. total and gradeCounter are both of type int. To return a non- int result from the equation, we need to specify a different type (ex: double ).

Primitive data types: numbers typebitsrange of values short 16-32,768 to +32,768 int 32-2,147,483,648 to +2,147,483,648 long 64-9,223,372,036,854,775,808 to +9,223,372,036,854,775,808 float E+38 to E+38 double E+308 to E+308

Primitive data types: other typebitsrange of values boolean 1true or false char 16‘\u0000’ to ‘\uFFFF’ Unicode character set byte to +127

Counter-controlled repetition: theory Counter-controlled repetition requires: 1. the name of a control variable (loop counter); 2. the initial value of the control variable; 3. the increment (or decrement) by which the control variable is modified each pass through the loop. 4. the condition that tests for the final value of the control variable.

Example: draw ten rectangles. //a while loop using counter-controlled repetition. import javax.swing.JApplet; //import JApplet class import java.awt.Graphics; //import Graphics class public class WhileCounter extends JApplet { //JApplet is superclass public void paint ( Graphics g ) //method for drawing { int count = 1; //counting repetitions int place = 25; //starting location for rectangle while ( count <= 10 ) { g.drawRect ( place, place, 40, 40 ); ++count; //increment count place += 15; //bump up place by 15 } name of control variable initial value increment condition for final value

the for repetition structure A more efficient way of creating a repetition structure: Contains all 4 elements necessary for repetition. for ( int count = 1; count <= 10; count++ ) name of control variable initial value increment condition for final value

What will be replaced. //a while loop using counter-controlled repetition. import javax.swing.JApplet; //import JApplet class import java.awt.Graphics; //import Graphics class public class WhileCounter extends JApplet { //JApplet is superclass public void paint ( Graphics g ) //method for drawing { int count = 1; //counting repetitions int place = 25; //starting location for rectangle while ( count <= 10 ) { g.drawRect ( place, place, 40, 40 ); ++count; //increment count place += 15; //bump up place by 15 }

the ‘for’ version //a ‘for’ loop alternative for counter-controlled repetition. import javax.swing.JApplet; //import JApplet class import java.awt.Graphics; //import Graphics class public class ForCounter extends JApplet { //JApplet is superclass public void paint ( Graphics g ) //method for drawing { int place = 25; //starting location for rectangle for ( int count = 1 ; count <= 10 ; ++count ) { g.drawRect ( place, place, 40, 40 ); place += 15; //bump up place by 15 }

Using for loops for animation: pt. 1 //a for loop as an alternative for counter-controlled repetition. import javax.swing.JApplet; //import JApplet class import java.awt.Graphics; //import Graphics class import java.awt.Color; //import Color class public class ForCounter3 extends JApplet { //JApplet is superclass public void paint ( Graphics g ) //method for drawing { int xPos = 25; //starting x location for rectangle int yPos = 25; //starting y location for rectangle boolean reverseX = false; //"which way to go" trigger boolean reverseY = false; //"which way to go" trigger get java file: ForCounter3

Using for loops for animation: pt. 2 for ( int count = 1 ; count <= 200 ; ++count ) { g.setColor(Color.white); g.drawRect ( xPos, yPos, 40, 40 ); if ( xPos < 300 && reverseX == false ) xPos += 15; //bump up xPos by 15 if xPos < 300 else { xPos -= 5; //reduce xPos by 12 if xPos >= 300 reverseX = true ; if ( xPos < 10 ) reverseX = false ; } get java file: ForCounter3

Using for loops for animation: pt. 3 if ( yPos < 250 && reverseY == false ) yPos += 10; //bump up yPos by 10 if yPos < 250 else { yPos -= 7; //reduce yPos by 7 if yPos >= 250 reverseY = true; if ( yPos < 10 ) reverseY = false; } g.setColor(Color.blue); g.drawRect ( xPos, yPos, 40, 40 ); //just to slow it down and look like animation for ( byte i = 1 ; i < 100 ; i++ ) repaint(); } get java file: ForCounter3

Program of the day pg. 167 Interest.java After you successfully run the program, alter it to use a “while” loop instead of a “for” loop. Tomorrow: Midterm Exam! –Everything through today’s lecture is fair game.