Inheritance in Java Mechanism of Deriving New Class

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Inheritance in Java allows the creation of new classes based on existing ones. The process involves deriving new classes from old classes, where the old class serves as the base, super, or parent class, and the new class as the derived, subclass, or child class. Types of inheritance include Single Inheritance, Multilevel Inheritance, Multiple Inheritance, and Hierarchical Inheritance. The mechanism involves constructing classes through subclass constructors using the super keyword to invoke superclass methods. However, Multiple Inheritance can lead to complexities due to dependencies on multiple base classes.

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JavaScript: Control Statements

CONTROL STRUCTURES JavaScript provides three selection structures. The if statement either performs (selects) an action if a condition is true or skips the action if the condition is false. Called a single-selection structure because it selects or ignores a single action or group of actions. The if else statement performs an action if a condition is true and performs a different action if the condition is false. Double-selection structure because it selects between two different actions or group of actions. The switch statement performs one of many different actions, depending on the value of an expression. Multiple-selection structure because it selects among many different actions or groups of actions.

CONTROL STRUCTURES CONT: JavaScript provides four repetition statements, namely, while, do while, for and for in. Keywords cannot be used as identifiers (e.g., for variable names).

JavaScript keywords break delete for new throw void Keywords that are reserved but not used by JavaScript abstract boolean const debugger extends final import int package private static super volatile case do function null true while catch else if return try with continue false in switch typeof default finally instanceof this var byte double float interface protected synchronized throws char enum goto long public class export implements native short transient

IF...ELSE SELECTION STATEMENT Conditional operator (?:) Closely related to the if else statement JavaScript s only ternary operator it takes three operands The operands together with the ?: operator form a conditional expression The first operand is a boolean expression The second is the value for the conditional expression if the boolean expression evaluates to true Third is the value for the conditional expression if the boolean expression evaluates to false

IF...ELSE SELECTION STATEMENT (CONT.) Nested if else statements Test for multiple cases by placing if else statements inside other if else structures The JavaScript interpreter always associates an else with the previous if, unless told to do otherwise by the placement of braces ({}) The if selection statement expects only one statement in its body To include several statements, enclose the statements in braces ({ and }) A set of statements contained within a pair of braces is called a block

IF...ELSE SELECTION STATEMENT (CONT.) A logic error has its effect at execution time. A fatal logic error causes a program to fail and terminate prematurely. A nonfatal logic error allows a program to continue executing, but the program produces incorrect results.

WHILE REPETITION STATEMENT while Allows the programmer to specify that an action is to be repeated while some condition remains true The body of a loop may be a single statement or a block Eventually, the condition becomes false and repetition terminates

FORMULATING ALGORITHMS: COUNTER-CONTROLLED REPETITION Counter-controlled repetition Often called definite repetition, because the number of repetitions is known before the loop begins executing A total is a variable in which a script accumulates the sum of a series of values Variables that store totals should normally be initialized to zero before they are used in a program A counter is a variable a script uses to count typically in a repetition statement

1 <?xml version = <?xml version = "1.0" 2 <!DOCTYPE html PUBLIC <!DOCTYPE html PUBLIC " "- -//W3C//DTD XHTML 1.0 Strict//EN" //W3C//DTD XHTML 1.0 Strict//EN" 3 "http://www.w3.org/TR/xhtml1/DTD/xhtml1 "http://www.w3.org/TR/xhtml1/DTD/xhtml1- -strict.dtd" 4 5 <!  > ate a class average. -- --> > Stores the sum of grades </title> Sets total to 0 Sets gradeCounter to 1 in preparation for the loop 10 ) // loop 10 times // loop 10 times Continues the cycle until gradeCounter is greater than 10 "Enter integer grade:", , "0" "0" ); );

29 // convert grade from a string to an integer // convert grade from a string to an integer 30 gradeValue = parseInt( grade ); gradeValue = parseInt( grade ); 31 32 // add gradeValue to total // add gradeValue to total 33 total = total + gradeValue; total = total + gradeValue; 34 35 // add 1 to gradeCounter // add 1 to gradeCounter 36 gradeCounter = gradeCounter + gradeCounter = gradeCounter +1 1; 37 } } // end while // end while 38 39 // Termination Phase // Termination Phase 40 average = total / average = total / 10 10; ; // calculate the average 41 42 // display average of exam grades // display average of exam grades 43 docum document.writeln( ent.writeln( 44 "<h1>Class average is " "<h1>Class average is " + average + 45 // // -- --> > 46 </script> </script> 47 </head> </head> 48 <body> <body> 49 <p> <p>Click Refresh (or Reload) to run the script again Click Refresh (or Reload) to run the script again<p> 50 </body> </body> 51 </html> </html> Increments gradeCounter by 1 after each iteration of the loop // calculate the average + average + "</h1>" "</h1>" ); ); <p>

1 <?xml version = <?xml version = "1.0" 2 <!DOCTYPE html PUBLIC <!DOCTYPE html PUBLIC " "- -//W3C//DTD XHTML 1.0 Strict//EN" //W3C//DTD XHTML 1.0 Strict//EN" 3 "http://www.w3.org/TR/xhtml1/DTD/xhtml1 "http://www.w3.org/TR/xhtml1/DTD/xhtml1- -strict.dtd" 4 5 <!  > --> > </title> controlled loop trolled loop 10 ) Outer control structure "Enter result (1=pass,2=fail)", "0" ); ); Start nested control structure End nested control structure Increment for while loop

31 // termination phase // termination phase 32 document.writeln( document.writeln( "<h1>Examination Results</h1>" "<h1>Examination Results</h1>" ); 33 document.writeln( document.writeln( 34 "Passed: " "Passed: " + passes + + passes + "<br />Failed: " 35 36 if if( passes > ( passes >8 8 ) 37 document.writeln document.writeln( "<br />Raise Tuition" 38 // // -- --> > 39 </script> </script> 40 </head> </head> 41 <body> <body> 42 <p> <p>Click Refresh (or Reload) to run the script again Click Refresh (or Reload) to run the script again</p> 43 </body> </body> 44 </html> </html> ); "<br />Failed: " + failures ); + failures ); Additional control structure "<br />Raise Tuition" ); </p>

ESSENTIALS OF COUNTER- CONTROLLED REPETITION Counter-controlled repetition requires name of a control variable initial value of the control variable the increment (or decrement) by which the control variable is modified each time through the loop the condition that tests for the final value of the control variable to determine whether looping should continue

1 <?xml version = <?xml version = "1.0" 2 <!DOCTYPE html PUBLIC <!DOCTYPE html PUBLIC " "- -//W3C//DTD XHTML 1.0 Strict//EN" //W3C//DTD XHTML 1.0 Strict//EN" 3 "http://www.w3.org/TR/xhtml1/DTD/xhtml1 "http://www.w3.org/TR/xhtml1/DTD/xhtml1- -strict.dtd" 4 5 <!  > 22 </script> </script> 23 </head><body></body> </head><body></body> 24 </html> </html> "1.0" encoding = encoding = "utf "utf- -8" 8"?> ?> strict.dtd"> > --> > --> > </title> Initializes counter Precedes the with a \ to create an escape sequence so that it can be used in the string ) // repetition condition // repetition condition "<p style = \ \"font "font- -size: " size: " + + ">XHTML font size " + counter + + counter + Condition to be fulfilled with every iteration Incrementing statement

FOR REPETITION STATEMENT for statement Specifies each of the items needed for counter-controlled repetition with a control variable Can use a block to put multiple statements into the body If the loop s condition uses a < or > instead of a <= or >=, or vice-versa, it can result in an off-by-one error for statement takes three expressions Initialization Condition Increment Expression The increment expression in the for statement acts like a stand-alone statement at the end of the body of the for statement Place only expressions involving the control variable in the initialization and increment sections of a for statement

1 <?xml version = <?xml version = "1.0" 2 <!DOCTYPE html PUBLIC <!DOCTYPE html PUBLIC " "- -//W3C//DTD XHTML 1.0 Strict//EN" //W3C//DTD XHTML 1.0 Strict//EN" 3 "http://www.w3.org/TR/xhtml1/DTD/xhtml1 "http://www.w3.org/TR/xhtml1/DTD/xhtml1- -strict.dtd" 4 5 <!  > 20 </script> </script> 21 </head><body></body> </head><body></body> 22 </html> </html> "1.0" encoding = encoding = "utf "utf- -8" 8"?> ?> strict.dtd"> > --> > he for statement. -- --> > </title> Initial value of the control variable on and Condition to test whether looping should continue ; counter <= 7 7; ++counter ) ; ++counter ) "<p style = \ \"font "font- -size: " size: " + + ">XHTML font size " + counter + + counter + Increment to occur after each iteration of the loop Statement inside the for loop

1 <?xml version = <?xml version = "1.0" 2 <!DOCTYPE html PUBLIC <!DOCTYPE html PUBLIC " "- -//W3C//DTD XHTML 1.0 Strict//EN" //W3C//DTD XHTML 1.0 Strict//EN" 3 "http://www.w3.org/TR/xhtml1/DTD/xhtml1 "http://www.w3.org/TR/xhtml1/DTD/xhtml1- -strict.dtd" 4 5 <!  > or loop. -- --> > </title> } left } } ; // principal amount // principal amount "1\ \">" ">" ); ); // begin the table // begin the table ); >" ); ); // year column heading // year column heading ); // amount column heading // amount column heading );

30 // output a table row for each year // output a table row for each year 31 for for ( ( var var year = year = 1 1; year <= 32 { { 33 amount = principal * Math.pow( amount = principal * Math.pow( 1.0 34 document.writeln( document.writeln( "<tr><td>" 35 "</td><td>" "</td><td>" + amount.toFixed( 36 "</td></tr>" "</td></tr>" ); 37 } } //end for //end for 38 39 document.writeln( document.writeln( "</tbody></table>" 40 // // -- --> > 41 </script> </script> 42 </head><body></body> </head><body></body> 43 </html> </html> ; year <= 10 10; ++year ) ; ++year ) Control variable year begins with a value of 1 1.0 + rate, year ); + rate, year ); "<tr><td>" + year + + year + + amount.toFixed(2 2) + ) + ); Continue to execute the loop while year is less than or equal to 10 "</tbody></table>" ); ); After each loop iteration, increase the value of year by 1

SWITCH MULTIPLE-SELECTION STATEMENT switch statement Consists of a series of case labels and an optional default case When control reaches a switch statement The script evaluates the controlling expression in the parentheses Compares this value with the value in each of the case labels If the comparison evaluates to true, the statements after the case label are executed in order until a break statement is reached The break statement is used as the last statement in each case to exit the switch statement immediately The default case allows you to specify a set of statements to execute if no other case is satisfied Usually the last case in the switch statement

SWITCH MULTIPLE-SELECTION STATEMENT (CONT.) Each case can have multiple actions (statements) Braces are not required around multiple actions in a case of a switch The break statement is not required for the last case because program control automatically continues with the next statement after the switch Having several case labels listed together (e.g., case 1: case 2: with no statements between the cases) executes the same set of actions for each case

1 <?xml version = <?xml version = "1.0" 2 <!DOCTYPE html PUBLIC <!DOCTYPE html PUBLIC " "- -//W3C//DTD XHTML 1.0 Strict//EN" //W3C//DTD XHTML 1.0 Strict//EN" 3 "http://www.w3.org/TR/xhtml1/DTD/xhtml1 "http://www.w3.org/TR/xhtml1/DTD/xhtml1- -strict.dtd" 4 5 <!  > selection statement. statement. -- --> > </title> ; // indicates if input is valid // indicates if input is valid Beginning of switch statement "Select a list style:\ \n" n" + + , "1" "1" ); ); Beginning of statements to be executed if choiceequals 1 Beginning of statements to be executed if choiceequals 2 Statements Break out of switch statement "list- -style style- -type: upper type: upper- -alpha alpha\ \">" ">"; ;

33 case 34 startTag = 35 endTag = 36 listType = 37 break 38 default 39 validInput = 40 } } //end switch //end switch 41 42 if if ( validInput == ( validInput == true 43 { { 44 document.writeln( listType + startTag ); document.writeln( listType + startTag ); 45 46 for for ( ( var var i = i = 1 1; i <= 47 document.writeln( document.writeln( "<li>List item " 48 49 document.writeln( endTag ); document.writeln( endTag ); 50 } } //end if //end if 51 else else 52 document.writeln( document.writeln( "Invalid choice: " 53 // // -- --> > 54 </script> </script> 55 </head> </head> 56 <body> <body> 57 <p> <p>Click Refresh (or Reload) to run the script again Click Refresh (or Reload) to run the script again</p> 58 </body> </body> 59 </html> </html> case "3" "3": : startTag = "<ol style = "<ol style = \ \"list "list- -style style- -type: upper type: upper- -roman roman\ \">" ">"; ; endTag = "</ol>" "</ol>"; ; listType = "<h1>Roman Numbered List</h1>" "<h1>Roman Numbered List</h1>"; ; break; ; default: : Beginning of statements to be executed if choice is anything other than 1 , 2 or 3 validInput = false false; ; true ) ) No break is necessary, since we ve come to the end of the switch anyway ; i <= 3 3; ++i ) ; ++i ) "<li>List item " + i + + i + "</li>" "</li>" ); ); "Invalid choice: " + cho + choice ); ice ); </p>

DOWHILE REPETITION STATEMENT do while statement tests the loop-continuation condition after the loop body executes The loop body always executes at least once

1 <?xml version = <?xml version = "1.0" 2 <!DOCTYPE html PUBLIC <!DOCTYPE html PUBLIC " "- -//W3C//DTD XHTML 1.0 Strict//EN" //W3C//DTD XHTML 1.0 Strict//EN" 3 "http://www.w3.org/TR/xhtml1/DTD/xhtml1 "http://www.w3.org/TR/xhtml1/DTD/xhtml1- -strict.dtd" 4 5 <!  > 21 </script> </script> 22 23 </head><body></body> </head><body></body> 24 </html> </html> "1.0" encoding = encoding = "utf "utf- -8" 8"?> ?> strict.dtd"> > --> > tement. -- --> > </title> Perform the following actions "<h" + counter + + counter + ">This is " ">This is " + + " level head" + + "</h" "</h" + + Then check to see if counter <= 6. If it is, iterate through the loop again. );

Inheritance in Java Mechanism of Deriving New Class

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