Chapter 5 - Control Structures - Part 2 Outline 5.1Introduction 5.2Essentials of Counter-Controlled Repetition 5.3The for Repetition Structure 5.4Examples Using the for Structure 5.5The switch Multiple-Selection Structure 5.6The do / while Repetition Structure 5.7The break and continue Statements 5.8The Labeled break and continue Statements 5.9Logical Operators 5.10Structured Programming Summary

5.2Counter-Controlled Repetition Example –Counter-controlled repetition

1. import 2. Class WhileCounter 3. paint 3.1 Initialize counter 3.2 Loop 3.3 drawLine 3.4 Increment Program Output 1// Fig. 5.1: WhileCounter.java 2// Counter-controlled repetition 3import java.awt.Graphics; 4import javax.swing.JApplet; 5 6public class WhileCounter extends JApplet { 7 public void paint( Graphics g ) 8 { 9 int counter = 1; // initialization while ( counter <= 10 ) { // repetition condition 12 g.drawLine( 10, 10, 250, counter * 10 ); 13 ++counter; // increment 14 } 15 } 16}

5.2Essentials of Counter-Controlled Repetition –Method drawLine( x1, y1, x2, y2 ) Called using reference to Graphics object Draws line from ( x1, y1 ) to ( x2, y2 ) 12 g.drawLine( 10, 10, 250, counter * 10 );

5.2Essentials of Counter-Controlled Repetition while ( ++counter <= 10 ) //repetition condition g.drawLine( 10, 10, 250, counter *10 ); Increment done inside while

5.3The for Repetition Structure Redo previous example –Use for structure

Loop using for Program Output 1// Fig. 5.2: ForCounter.java 2// Counter-controlled repetition with the for structure 3import java.awt.Graphics; 4import javax.swing.JApplet; 5 6public class ForCounter extends JApplet { 7 public void paint( Graphics g ) 8 { 9 // Initialization, repetition condition and incrementing 10 // are all included in the for structure header. 11 for ( int counter = 1; counter <= 10; counter++ ) 12 g.drawLine( 10, 10, 250, counter * 10 ); 13 } 14}

5.3The for Repetition Structure –for "does it all" : initialization, condition, increment –General format for ( initialization ; loopContinuationTest ; increment ) statement If multiple statements needed, enclose in braces 11 for ( int counter = 1; counter <= 10; counter++ ) 12 g.drawLine( 10, 10, 250, counter * 10 );

5.3The for Repetition Structure May use arithmetic expressions in for loops –Let x =2, y=10 for ( int j = x; j <= 4 * x * y; j += y / x ) is equivalent to for ( int j = 2; j <= 80; j += 5 ) for can usually be written as a while loop: –Exception in section 5.7 initialization ; while ( loopContinuationTest ) { statement increment ; }

5.3The for Repetition Structure 11 for ( int counter = 1; counter <= 10; counter++ ) 12 g.drawLine( 10, 10, 250, counter * 10 ); true false int counter = 1 counter <= 10 counter++ g.drawLine( 10, 10, 250, counter * 10 ); Establish initial value of control variable. Determine if final value of control variable has been reached. Body of loop (this may be many statements) Increment the control variable.

5.4Examples Using the for Structure Problem –Calculate the value each year of a $1000 deposit, yielding 5% annually Calculate the value for 10 years –Use a = p (1 + r ) p - principal r - interest rate n - number of years a - amount on deposit after nth year Example program –Use a for loop to calculate interest n

Use for loop to calculate interest 1// Fig. 5.6: Interest.java 2// Calculating compound interest 3import java.text.DecimalFormat; 4import javax.swing.JOptionPane; 5import javax.swing.JTextArea; 6 7public class Interest { 8 public static void main( String args[] ) 9 { 10 double amount, principal = , rate =.05; DecimalFormat precisionTwo = new DecimalFormat( "0.00" ); 13 JTextArea outputTextArea = new JTextArea( 11, 20 ); outputTextArea.append( "Year\tAmount on deposit\n" ); for ( int year = 1; year <= 10; year++ ) { 18 amount = principal * Math.pow( rate, year ); 19 outputTextArea.append( year + "\t" + 20 precisionTwo.format( amount ) + "\n" ); 21 } JOptionPane.showMessageDialog( 24 null, outputTextArea, "Compound Interest", 25 JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); // terminate the application 28 } 29}

Program Output

5.4Examples Using the for Structure –Variables used –Class DecimalFormat (package java.text ) Passed format control string " 0.00" Exactly two digits to right of decimal, at least one to left Method format returns formatted String –Class JTextArea (package javax.swing ) GUI component, can display many lines of text Initialized to display 11 rows and 20 columns of text 10 double amount, principal = , rate =.05; 12 DecimalFormat precisionTwo = new DecimalFormat( "0.00" ); 13 JTextArea outputTextArea = new JTextArea( 11, 20 );

5.4Examples Using the for Structure –Method append (of class JTextArea ) Add text to the String already in JTextArea object Initially contains empty string –for loop executes 10 times –static method pow (class Math ) Math.pow( x, y ) Raises x to the y th power Takes two double s, returns a double 15 outputTextArea.append( "Year\tAmount on deposit\n" ); 21 } 17 for ( int year = 1; year <= 10; year++ ) { 18 amount = principal * Math.pow( rate, year ); 19 outputTextArea.append( year + "\t" + 20 precisionTwo.format( amount ) + "\n" );

5.4Examples Using the for Structure –static method showMessageDialog Class JOptionPane Up till now, displayed String s showMessageDialog can display a String or GUI component, such as a JTextArea 23 JOptionPane.showMessageDialog( 24 null, outputTextArea, "Compound Interest", 25 JOptionPane.INFORMATION_MESSAGE );

1. import 2. Class Interest 2.1 Initialize variables 2.2 DecimalFormat 3. for loop 3.1 Math.pow 3.2 append 3.3 format 3.4 showMessageDialog 1// Fig. 5.6: Interest.java 2// Calculating compound interest 3 3import java.text.DecimalFormat; 4import javax.swing.JOptionPane; 5import javax.swing.JTextArea; 6 7public class Interest { 8 public static void main( String args[] ) 9 { 10 double amount, principal = , rate =.05; DecimalFormat precisionTwo = new DecimalFormat( "0.00" ); JTextArea outputTextArea = new JTextArea( 11, 20 ); outputTextArea.append( "Year\tAmount on deposit\n" ); for ( int year = 1; year <= 10; year++ ) { amount = principal * Math.pow( rate, year ); outputTextArea.append( year + "\t" precisionTwo.format( amount ) + "\n" ); 21 } JOptionPane.showMessageDialog( 24 null, outputTextArea, "Compound Interest", 25 JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); // terminate the application 28 } 29} Notice the import statements required. New JTextArea object initialized to hold 11 rows and 20 columns of text. new operator used to create new objects. Use method append to add to the String in the JTextArea object. Notice the format of method Math.pow Use method format to output the formatted number as a String. Use the JTextArea reference as an argument to showMessageDialog

Program Output

5.5The switch Multiple-Selection Structure switch statements –Useful to test a variable for different values Different action taken Format –Series of case labels and an optional default case switch ( value ){ case '1': actions case '2': actions default: actions } –break; causes exit from structure

5.5The switch Multiple-Selection Structure true false case a case a action(s)break case b case b action(s)break false case z case z action(s)break true default action(s)

Class SwitchTest 1// Fig. 5.7: SwitchTest.java 2// Counting letter grades 3import java.awt.Graphics; 4import javax.swing.*; 5 6public class SwitchTest extends JApplet { 7 int choice; 8 9 public void init() 10 { 11 String input; input = JOptionPane.showInputDialog( 14 "Enter 1 to draw lines\n" + 15 "Enter 2 to draw rectangles\n" + 16 "Enter 3 to draw ovals\n" ); choice = Integer.parseInt( input ); 19 } public void paint( Graphics g ) 22 { 23 for ( int i = 0; i < 10; i++ ) { 24 switch( choice ) { 25 case 1: 26 g.drawLine( 10, 10, 250, 10 + i * 10 ); 27 break; 28 case 2: 29 g.drawRect( 10 + i * 10, 10 + i * 10, i * 10, 50 + i * 10 ); 31 break;

Program Output i * 10, 50 + i * 10 ); 35 break; 36 default: 37 JOptionPane.showMessageDialog( 38 null, "Invalid value entered" ); 39 } // end switch 40 } // end for 41 } // end paint() 42} // end class SwitchTest 32 case 3: 33 g.drawOval( 10 + i * 10, 10 + i * 10,

Program Output

5.5The switch Multiple-Selection Structure –Method init Get input from user 9 public void init() 10 { 11 String input; input = JOptionPane.showInputDialog( 14 "Enter 1 to draw lines\n" + 15 "Enter 2 to draw rectangles\n" + 16 "Enter 3 to draw ovals\n" ); choice = Integer.parseInt( input ); 19 } 7 int choice;

5.5The switch Multiple-Selection Structure –switch structure - compare choice to case s case labels - can be constant integral values of type byte, short, int, long, and char –Use single quotes to represent characters: 'A' –Can have multiple actions per case break - exits switch structure default label - optional, actions to take if no cases met 24 switch( choice ) { 25 case 1: 26 g.drawLine( 10, 10, 250, 10 + i * 10 ); 27 break; 36 default: 37 JOptionPane.showMessageDialog( 38 null, "Invalid value entered" );

5.6The do / while Repetition Structure The do/while repetition structure –Similar to the while structure –Condition for repetition tested after the body of the loop is performed –Actions are performed at least once Format – do { statement } while ( condition ); –Good practice to put brackets in, even if not required

5.6The do / while Repetition Structure true false action(s) condition

1. Class DoWhileTest 2. paint 3. do / while loop Program Output 1// Fig. 5.9: DoWhileTest.java 2// Using the do/while repetition structure 3import java.awt.Graphics; 4import javax.swing.JApplet; 5 6public class DoWhileTest extends JApplet { 7 public void paint( Graphics g ) 8 { 9 int counter = 1; do { g.drawOval( counter * 10, counter * 10, 13 counter * 20, counter * 20 ); 14 ++counter; 15 } while ( counter <= 10 ); 16 } 17}

5.7The break and continue Statements break –Immediate exit from while, for, do/while or switch –Program continues with the first statement after the structure –Common uses of the break statement Escape early from a loop Skip the remainder of a switch structure

5.7The break and continue Statements continue –Skips the remaining statements in body of while, for or do/while Proceeds with the next iteration of the loop –while and do/while Loop-continuation test is evaluated immediately after continue –for structure Increment expression is executed, then the loop-continuation test is evaluated

1. Class BreakTest 2. main 2.1 for loop 2.2 break Program Output 1// Fig. 5.11: BreakTest.java 2// Using the break statement in a for structure 3import javax.swing.JOptionPane; 4 5public class BreakTest { 6 public static void main( String args[] ) 7 { 8 String output = ""; 9 int count; for ( count = 1; count <= 10; count++ ) { 12 if ( count == 5 ) break; // break loop only if count == output += count + " "; 16 } output += "\nBroke out of loop at count = " + count; 19 JOptionPane.showMessageDialog( null, output ); 20 System.exit( 0 ); 21 } 22} break causes an immediate exit from the loop.

1. Class ContinueTest 2. main 2.1 for loop 2.2 continue Program Output 1// Fig. 5.12: ContinueTest.java 2// Using the continue statement in a for structure 3import javax.swing.JOptionPane; 4 5public class ContinueTest { 6 public static void main( String args[] ) 7 { 8 String output = ""; 9 10 for ( int count = 1; count <= 10; count++ ) { 11 if ( count == 5 ) continue; // skip remaining code in loop 13 // only if count == output += count + " "; 16 } output += "\nUsed continue to skip printing 5"; 19 JOptionPane.showMessageDialog( null, output ); 20 System.exit( 0 ); 21 } continue skips the rest of the body and goes to the next iteration.

5.8The Labeled break and continue Statements Nested set of structures –break statement Can only break out of immediately enclosing structure –Use labeled break statement Label - identifier followed by colon, i.e. myLabel: Breaks out of enclosing statement and any number of repetition structures Program resumes after enclosing labeled compound statement –Labeled continue statement Skips statements in enclosing structure Continues with next iteration of enclosing labeled repetition structure –Repetition structure preceded by a label

1. Class BreakLabelTest 2. stop: 2.1 for loop 2.2 Nested for loop 2.3 break stop 1// Fig. 5.13: BreakLabelTest.java 2// Using the break statement with a label 3import javax.swing.JOptionPane; 4 5public class BreakLabelTest { 6 public static void main( String args[] ) 7 { 8 String output = ""; stop: { // labeled compound statement 11 for ( int row = 1; row <= 10; row++ ) { 12 for ( int column = 1; column <= 5 ; column++ ) { if ( row == 5 ) break stop; // jump to end of stop block output += "* "; 18 } output += "\n"; 21 } // the following line is skipped 24 output += "\nLoops terminated normally"; 25 } 26 Begins labeled compound statement stop: Labeled break statement to exit stop block.

Program Output 27 JOptionPane.showMessageDialog( 28 null, output,"Testing break with a label", 29 JOptionPane.INFORMATION_MESSAGE ); 30 System.exit( 0 ); 31 } 32}

1. Class ContinueLabelTest 2. nextRow: 2.1 for loop 2.2 Nested for loop 2.3 continue nextRow 1// Fig. 5.14: ContinueLabelTest.java 2// Using the continue statement with a label 3import javax.swing.JOptionPane; 4 5public class ContinueLabelTest { 6 public static void main( String args[] ) 7 { 8 String output = ""; nextRow: // target label of continue statement 11 for ( int row = 1; row <= 5; row++ ) { 12 output += "\n"; for ( int column = 1; column <= 10; column++ ) { if ( column > row ) 17 continue nextRow; // next iteration of 18 // labeled loop output += "* "; 21 } 22 } JOptionPane.showMessageDialog( 25 null, output,"Testing continue with a label", 26 JOptionPane.INFORMATION_MESSAGE ); 27 System.exit( 0 ); 28 } 29} This label applies to the following for loop (labeled repetition structure). Labeled continue statement skips remaining statements, goes to next iteration of labeled repetition structure.

Program Output

5.9Logical Operators Logical Operators –Till now, used, ==, etc to test conditions –Logical operators allow more complex conditions –&& (logical AND) Returns true if both conditions are true –|| (logical OR) Returns true if either of its conditions are true –! (logical NOT, logical negation) Reverses the truth/falsity of its condition –Short circuit evaluation Evaluate left operand, decide whether to evaluate right operand If left operand of && is false, will not evaluate right operand

5.9Logical Operators Boolean Logical Operators –^ (Boolean logical exclusive OR) true if exactly one condition true –Boolean logical AND ( & ) and boolean logical inclusive OR ( | ) Work identical to regular logical AND and logical OR Always evaluates both expressions (no short-circuit evaluation) Useful if right operand has a needed side effect birthday == true | ++age >= 65

5.9Logical Operators Examples ExpressionResult true && false false true || false true !false true true ^ truefalse

1. Class LogicalOperators 1.1 JTextArea 1.2 JScrollPane 2. Logical operators 1// Fig. 5.19: LogicalOperators.java 2// Demonstrating the logical operators 3import javax.swing.*; 4 5public class LogicalOperators { 6 public static void main( String args[] ) 7 { 8 8 JTextArea outputArea = new JTextArea( 17, 20 ); 9 9 JScrollPane scroller = new JScrollPane( outputArea ); 10 String output = ""; output += "Logical AND (&&)" "\nfalse && false: " + ( false && false ) + 14 "\nfalse && true: " + ( false && true ) + 15 "\ntrue && false: " + ( true && false ) + 16 "\ntrue && true: " + ( true && true ); output += "\n\nLogical OR (||)" + 19 "\nfalse || false: " + ( false || false ) + 20 "\nfalse || true: " + ( false || true ) + 21 "\ntrue || false: " + ( true || false ) + 22 "\ntrue || true: " + ( true || true ); output += "\n\nBoolean logical AND (&)" + 25 "\nfalse & false: " + ( false & false ) + 26 "\nfalse & true: " + ( false & true ) + 27 "\ntrue & false: " + ( true & false ) + 28 "\ntrue & true: " + ( true & true ); 29 JTextArea can display many lines of text. This one can display 17 rows and 20 columns. This creates a JScrollPane object and initializes it with outputArea. This adds scrolling to outputArea. Use the logical operators. Boolean values converted to String s.

3. setText 34 "\ntrue | true: " + ( true | true ); output += "\n\nBoolean logical exclusive OR (^)" + 37 "\nfalse ^ false: " + ( false ^ false ) + 38 "\nfalse ^ true: " + ( false ^ true ) + 39 "\ntrue ^ false: " + ( true ^ false ) + 40 "\ntrue ^ true: " + ( true ^ true ); output += "\n\nLogical NOT (!)" + 43 "\n!false: " + ( !false ) + 44 "\n!true: " + ( !true ); outputArea.setText( output ); 47 JOptionPane.showMessageDialog( null, scroller, 48 "Truth Tables", JOptionPane.INFORMATION_MESSAGE ); 49 System.exit( 0 ); 50 } 51} 30 output += "\n\nBoolean logical inclusive OR (|)" + 31 "\nfalse | false: " + ( false | false ) + 32 "\nfalse | true: " + ( false | true ) + 33 "\ntrue | false: " + ( true | false ) + Method setText replaces the String in the JTextArea.

5.10Structured Programming Summary Rule 3 Rule 3 - Replace any rectangle with a control structure