Chapter 4 Control Structures: Part 2

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1 Chapter 4 Control Structures: Part 2 1

2 2 Essentia ls of Counter-Controlled Repetition Counter-controlled repetition requires: Control variable (loop counter) Initial value of the control variable Increment/decrement of control variable through each loop Condition that tests for the final value of the control variable 2003 Prentice Hall, Inc. All rights reserved.

3 1 // Fig. 5.1: WhileCounter.java 2 // Counter-controlled repetition. 3 import java.awt.graphics; 4 5 import javax.swing.japplet; 6 7 public class WhileCounter extends JApplet { Control-variable Condition name is counter tests for counter s final value Control-variable initial value is // draw lines on applet s background 10 public void paint( Graphics g ) 11 { 12 super.paint( g ); // call paint method inherited from JApplet int counter = 1; // initialization while ( counter <= 10 ) { // repetition condition 17 g.drawline( 10, 10, 250, counter * 10 ); 18 ++counter; // increment } // end while } // end method paint } // end class WhileCounter Outline WhileCounter.ja va Line 14 Line 16 Increment Line for counter Prentice Hall, Inc. All rights reserved.

4 for Repetition Statement 4 import java.awt.graphics; import javax.swing.japplet; public class ForCounter extends JApplet { // draw lines on applet s background public void paint( Graphics g ) { super.paint( g ); // call paint method inherited from Japplet for ( int counter = 1; counter <= 10; counter++ ) g.drawline( 10, 10, 250, counter * 10 ); } }

5 5 for keyword Control variable Required semicolon separator Final value of control variable for which the condition is true Required semicolon separator for ( int counter = 1; counter <= 10; counter++ ) Initial value of control variable Loop-continuation condition Increment of control variable for statement header components Prentice Hall, Inc. All rights reserved.

6 for Repetition Structure (cont.) 6 for ( initialization; loopcontinuationcondition; increment ) statement; can usually be rewritten as: initialization; while ( loopcontinuationcondition ) { statement; increment; } 2003 Prentice Hall, Inc. All rights reserved.

7 7 Establish initial value of control variable int counter = 1 [counter > 10] [counter <= 10] Draw a line on the applet Increment the control variable Determine whether the final value of control variable has been reached g.drawline( 10, 10, 250, counter * 10 ); counter++ for statement activity diagram Prentice Hall, Inc. All rights reserved.

8 8 4.4 Exa mples Using the for Sta tement Varying control variable in for statement Vary control variable from 1 to 100 in increments of 1 for ( int i = 1; i <= 100; i++ ) Vary control variable from 100 to 1 in increments of 1 for ( int i = 100; i >= 1; i-- ) Vary control variable from 7 to 77 in increments of 7 for ( int i = 7; i <= 77; i += 7 ) 2003 Prentice Hall, Inc. All rights reserved.

9 1 // Fig. 5.5: Sum.java 2 // Summing integers with the for statement. 3 import javax.swing.joptionpane; 4 5 public class Sum { 6 7 public static void main( String args[] ) 8 { 9 int total = 0; // initialize sum // total even integers from 2 through for ( int number = 2; number <= 100; number += 2 ) 13 total += number; // display results 16 JOptionPane.showMessageDialog( null, "The sum is " + total, 17 "Total Even Integers from 2 to 100", 18 JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); // terminate application } // end main } // end class Sum increment number by 2 each iteration Outline Sum.java Line Prentice Hall, Inc. All rights reserved.

10 10 do while Repetition Sta tement do while structure Similar to while structure Tests loop-continuation after performing body of loop i.e., loop body always executes at least once 2003 Prentice Hall, Inc. All rights reserved.

11 1 // Fig. 5.7: DoWhileTest.java 2 // Using the do...while statement. 3 import java.awt.graphics; 4 5 import javax.swing.japplet; 6 Oval is drawn before testing 7 public class DoWhileTest extends JApplet { 8 counter s final value 9 // draw lines on applet 10 public void paint( Graphics g ) 11 { 12 super.paint( g ); // call paint method inherited from JApplet int counter = 1; // initialize counter do { 17 g.drawoval( counter * 10, counter * 10, 18 counter * 20, counter * 20 ); 19 ++counter; 20 } while ( counter <= 10 ); // end do...while } // end method paint } // end class DoWhileTest Outline 11 DoWhileTest.jav a Lines Prentice Hall, Inc. All rights reserved.

14 1 // Fig. 5.9: SwitchTest.java 2 // Drawing lines, rectangles or ovals based on user input. 3 import java.awt.graphics; 4 5 import javax.swing.*; 6 7 public class SwitchTest extends JApplet { 8 int choice; // user's choice of which shape to draw 9 10 // initialize applet by obtaining user's choice 11 public void init() 12 { 13 String input; // user's input Get user s input in JApplet // obtain user's choice 16 input = JOptionPane.showInputDialog( 17 "Enter 1 to draw lines\n" + 18 "Enter 2 to draw rectangles\n" + 19 "Enter 3 to draw ovals\n" ); choice = Integer.parseInt( input ); // convert input to int } // end method init // draw shapes on applet's background 26 public void paint( Graphics g ) 27 { 28 super.paint( g ); // call paint method inherited from JApplet for ( int i = 0; i < 10; i++ ) { // loop 10 times (0-9) 31 Outline 2003 Prentice Hall, Inc. All rights reserved. 14 SwitchTest.java Lines 16-21: Getting user s input

15 32 switch ( choice ) { // determine shape to draw case 1: // draw a line 35 g.drawline( 10, 10, 250, 10 + i * 10 ); 36 break; // done processing case case 2: // draw a rectangle 39 g.drawrect( 10 + i * 10, 10 + i * 10, i * 10, 50 + i * 10 ); 41 break; // done processing case case 3: // draw an oval 44 g.drawoval( 10 + i * 10, 10 + i * 10, i * 10, 50 + i * 10 ); 46 break; // done processing case default: // draw string indicating invalid value entered 49 g.drawstring( "Invalid value entered", 50 10, 20 + i * 15 ); } // end switch } // end for } // end method paint } // end class SwitchTest Outline user input (choice) is switch controlling statement expression determines which case label to execute, SwitchTest.java depending on controlling expression Line 32: controlling expression Line 32: switch statement Line 48 default case for invalid entries Prentice Hall, Inc. All rights reserved.

18 18 case a [fa lse] [true] case a ac tion(s) break case b [fa lse] [true] case b ac tion(s) break. [true] case z [fa lse] case z ac tion(s) break default ac tion(s) Fig switch multiple-selection sta tement a ctivity dia gra m with break sta tements Prentice Hall, Inc. All rights reserved.

19 19 break a nd continue Sta tements break/continue Alter flow of control break statement Causes immediate exit from control structure Used in while, for, do while or switch statements continue statement Skips remaining statements in loop body Proceeds to next iteration Used in while, for or do while statements 2003 Prentice Hall, Inc. All rights reserved.

20 1 // Fig. 5.11: BreakTest.java 2 // Terminating a loop with break. 3 import javax.swing.joptionpane; 4 5 public class BreakTest { 6 7 public static void main( String args[] ) 8 { 9 String output = ""; 10 int count; for ( count = 1; count <= 10; count++ ) { // loop 10 times if ( count == 5 ) // if count is 5, 15 break; // terminate loop output += count + " "; } // end for output += "\nbroke out of loop at count = " + count; 22 JOptionPane.showMessageDialog( null, output ); System.exit( 0 ); // terminate application } // end main } // end class BreakTest Outline BreakTest.java exit for structure (break) Line 12 when count equals 5 Loop 10 times Lines Prentice Hall, Inc. All rights reserved.

21 1 // Fig. 5.12: ContinueTest.java 2 // Continuing with the next iteration of a loop. 3 import javax.swing.joptionpane; 4 5 public class ContinueTest { 6 7 public static void main( String args[] ) 8 { 9 String output = ""; for ( int count = 1; count <= 10; count++ ) { // loop 10 times if ( count == 5 ) // if count is 5, 14 continue; // skip remaining code in loop output += count + " "; } // end for output += "\nused continue to skip printing 5"; 21 JOptionPane.showMessageDialog( null, output ); System.exit( 0 ); // terminate application } // end main } // end class ContinueTest Outline ContinueTest.ja Skip line 16 and proceed va to line 11 when count equals 5 Loop 10 times Line 11 Lines Prentice Hall, Inc. All rights reserved.

22 22 Labeled break and continue Statements Labeled block Set of statements enclosed by {} Preceded by a label Labeled break statement Exit from nested control structures Proceeds to end of specified labeled block Labeled continue statement Skips remaining statements in nested-loop body Proceeds to beginning of specified labeled block 2003 Prentice Hall, Inc. All rights reserved.

23 1 // Fig. 5.13: BreakLabelTest.java 2 // Labeled break statement. 3 import javax.swing.joptionpane; 4 5 public class BreakLabelTest { 6 stop is the labeled block 7 public static void main( String args[] ) 8 { 9 String output = ""; stop: { // labeled block // count 10 rows 14 for ( int row = 1; row <= 10; row++ ) { // count 5 columns 17 for ( int column = 1; column <= 5 ; column++ ) { if ( row == 5 ) // if row is 5, 20 break stop; // jump to end of stop block output += "* "; } // end inner for output += "\n"; } // end outer for 29 Loop 10 times Nested loop 5 times Exit to line 35 (next slide) Outline 23 BreakLabelTest. java Line 11 Line 14 Line 17 Lines Prentice Hall, Inc. All rights reserved.

$30 // following line is skipped 31 output += "\nloops terminated normally"; 32 33 } // end labeled block 34 35 JOptionPane.$

24 30 // following line is skipped 31 output += "\nloops terminated normally"; } // end labeled block JOptionPane.showMessageDialog( null, output, 36 "Testing break with a label", 37 JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); // terminate application } // end main } // end class BreakLabelTest Outline 24 BreakLabelTest. java 2003 Prentice Hall, Inc. All rights reserved.

25 1 // Fig. 5.14: ContinueLabelTest.java 2 // Labeled continue statement. 3 import javax.swing.joptionpane; 4 5 public class ContinueLabelTest { 6 nextrow is the labeled block 7 public static void main( String args[] ) 8 { 9 String output = ""; Loop 5 times nextrow: // target label of continue statement // count 5 rows 14 for ( int row = 1; row <= 5; row++ ) { 15 output += "\n"; // count 10 columns per row 18 for ( int column = 1; column <= 10; column++ ) { // if column greater than row, start next row 21 if ( column > row ) 22 continue nextrow; // next iteration of labeled loop output += "* "; } // end inner for } // end outer for Nested loop 10 times Outline 25 ContinueLabelTe st.java Line 11 Line 14 Line 17 Lines continue to line 11 (nextrow) 2003 Prentice Hall, Inc. All rights reserved.

29 30 JOptionPane.showMessageDialog( null, output, 31 "Testing continue with a label", 32 JOptionPane.INFORMATION_MESSAGE ); 33 34 System.

26 29 30 JOptionPane.showMessageDialog( null, output, 31 "Testing continue with a label", 32 JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); // terminate application } // end main } // end class ContinueLabelTest Outline 26 ContinueLabelTe st.java 2003 Prentice Hall, Inc. All rights reserved.

27 27 Logica l Opera tors Logical operators Allows for forming more complex conditions Combines simple conditions Java logical operators && (conditional AND) & (boolean logical AND) (conditional OR) (boolean logical inclusive OR) ^ (boolean logical exclusive OR)! (logical NOT) 2003 Prentice Hall, Inc. All rights reserved.

28 28 expression1 expression2 expression1 && expression2 false false false false true false true false false true true true Fig && (conditional AND) operator truth table. expression1 expression2 expression1 expression2 false false false false true true true false true true true true Fig (conditional OR) operator truth table Prentice Hall, Inc. All rights reserved.

29 29 expression1 expression2 expression1 ^ expression2 false false false false true true true false true true true false Fig ^ (boolean logical exclusive OR) operator truth table. expression!expression false true true false Fig. 5.18! (logical negation, or logical NOT) operator truth table Prentice Hall, Inc. All rights reserved.

30 1 // Fig. 5.19: LogicalOperators.java 2 // Logical operators. 3 import javax.swing.*; 4 5 public class LogicalOperators 6 7 public static void main( String args[] ) 8 { 9 // create JTextArea to display results 10 JTextArea outputarea = new JTextArea( 17, 20 ); // attach JTextArea to a JScrollPane so user can scroll results 13 JScrollPane scroller = new JScrollPane( outputarea ); // create truth table for && (conditional AND) operator 16 String output = "Logical AND (&&)" + 17 "\nfalse && false: " + ( false && false ) + 18 "\nfalse && true: " + ( false && true ) + 19 "\ntrue && false: " + ( true && false ) + 20 "\ntrue && true: " + ( true && true ); // create truth table for (conditional OR) operator 23 output += "\n\nlogical OR ( )" + 24 "\nfalse false: " + ( false false ) + 25 "\nfalse true: " + ( false true ) + 26 "\ntrue false: " + ( true false ) + 27 "\ntrue true: " + ( true true ); 28 Conditional AND truth table Outline 30 LogicalOperator s.java Lines Lines Conditional OR truth table 2003 Prentice Hall, Inc. All rights reserved.

31 29 // create truth table for & (boolean logical AND) operator 30 output += "\n\nboolean logical AND (&)" + 31 "\nfalse & false: " + ( false & false ) + 32 "\nfalse & true: " + ( false & true ) + 33 "\ntrue & false: " + ( true & false ) + 34 "\ntrue & true: " + ( true & true ); 35 Boolean logical AND truth table 36 // create truth table for (boolean logical inclusive OR) operator 37 output += "\n\nboolean logical inclusive OR ( )" + 38 "\nfalse false: " + ( false false ) + 39 "\nfalse true: " + ( false true ) + 40 "\ntrue false: " + ( true false ) + 41 "\ntrue true: " + ( true true ); // create truth table for ^ (boolean logical exclusive OR) operator 44 output += "\n\nboolean logical exclusive OR (^)" + 45 "\nfalse ^ false: " + ( false ^ false ) + 46 "\nfalse ^ true: " + ( false ^ true ) + 47 "\ntrue ^ false: " + ( true ^ false ) + 48 "\ntrue ^ true: " + ( true ^ true ); // create truth table for! (logical negation) operator 51 output += "\n\nlogical NOT (!)" + 52 "\n!false: " + (!false ) + 53 "\n!true: " + (!true ); outputarea.settext( output ); // place results in JTextArea 56 Outline 31 LogicalOperator s.java Lines Lines Boolean logical inclusive Lines OR truth table Lines Boolean logical exclusive OR truth table Logical NOT truth table 2003 Prentice Hall, Inc. All rights reserved.

57 JOptionPane.showMessageDialog( null, scroller, 58 "Truth Tables", JOptionPane.INFORMATION_MESSAGE ); 59 60 System.

32 57 JOptionPane.showMessageDialog( null, scroller, 58 "Truth Tables", JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); // terminate application } // end main } // end class LogicalOperators Outline 32 LogicalOperator s.java 2003 Prentice Hall, Inc. All rights reserved.

33 33 Operators Associativity Type right to left unary postfix ! (type) right to left unary * / % left to right multiplicative + - left to right additive < <= > >= left to right relational ==!= left to right equality & left to right boolean logical AND ^ left to right boolean logical exclusive OR left to right boolean logical inclusive OR && left to right conditional AND left to right conditional OR?: right to left conditional = += - = *= /= %= right t o left assignment Fig Precedence/associativity of the operators discussed so far Prentice Hall, Inc. All rights reserved.

Chapter 5 Control Structures: Part 2

Chapter 5 Control Structures: Part 2 Essentials of Counter-Controlled Repetition Counter-controlled repetition requires: Name of control variable (loop counter) Initial value of control variable Increment/decrement