java™ how to program, 10/e late objects version © 1992-2015 by pearson education, inc. all rights...

Java™ How to Program, 10/eLate Objects Version

© 1992-2015 by Pearson Education, Inc. All Rights Reserved.

Repetition statement—repeats an action while a condition remains true.

PseudocodeWhile there are more items on my shopping list

Purchase next item and cross it off my list The repetition statement’s body may be a single

statement or a block. Eventually, the condition will become false. At this

point, the repetition terminates, and the first statement after the repetition statement executes.


Example of Java’s while repetition statement: find the first power of 3 larger than 100. Suppose that the int variable product is initialized to 3.

while (product <= 100) product = 3 * product;

Each iteration multiplies product by 3, so product takes on the values 9, 27, 81 and 243 successively.

When product becomes 243—product <= 100—becomes false.

Repetition terminates. The final value of product is 243. Program execution continues with the next statement after

the while statement.


while statement activity diagram . The UML represents both the merge symbol and the decision

symbol as diamonds. The merge symbol joins two flows of activity into one. The decision and merge symbols can be distinguished by the

number of “incoming” and “outgoing” transition arrows. A decision symbol has one transition arrow pointing to the diamond and

two or more pointing out from it to indicate possible transitions from that point. Each transition arrow pointing out of a decision symbol has a guard condition next to it.

A merge symbol has two or more transition arrows pointing to the diamond and only one pointing from the diamond, to indicate multiple activity flows merging to continue the activity. None of the transition arrows associated with a merge symbol has a guard condition.


Java syntax while (condition) while (condition) { statement; statement; the statement can be a statement;. single statement or a block ... statement; } As long as the condition is true perform the

statements in the while block at the end of the block go back to the begining test

the condition and so on...

Comparing while with if while (condition) if (condition) { { statement; statement; statement;. statement; ... statement; statement; } } In if – block is evaluated onece and control is passed

to the next line In while – block is evaluated as long as at the end

condition is true

Example 4.1 Task: Write the inegers from 1 to 10 to the

screen

Example 4.1

1 Start2 Declare Integer i =13 WHILE i <= 10 Display i Set i = 1++1 // increment i by one End While4 End

Explanation of the pseudocode WHILE i <=10 the condition is:

i <=10 to evalutate this condition initially value of i must be known so i is initialized to 1 before WHILE

The actions repeatatly performed are print i increment i by one

after performing the second step the condition is rechecked if true: i is still less then or equal to 10 the value of i displaied and incremented when i becomes 11 the condition is false hence value of i is

not prited to the screen

Counter variable A variable is needed taking values from 1 to

10 At each interattion

current value of the variable is printed its value is incremented by one

Otherwise the action is: print 1 print 2 ... print 9 print 10

Java code – main block

{ // begining method main int i = 1; // declare and initialize an integer

while( i <= 10) { // as long as i <=10 do

System.ou.printf(“%d\n”,i); i = i+1; // increment i } // end while block} // end method main

Important Sequence of actions

print and increment

initial value of i: i=1 statemet of the condition: i <= 10 condition chaning statement: i = 1 + 1; usually at the last statement in the while

block ARE IMPORTANT

Compering alternative sequensing Sequence of actions

print increment increment print

initial value of i i = 1 or i = 0

statemet of the conditin i <= 10 i < 10

Another sequence of actions1 Start2 Declare Integer i = 03 WHILE i <10 Set i = i+1//increment i by one – condition chaning Display i End While4 End if the order of actions are changed i shold be inilized to 0 condition becomes i < 10 or i <=9

Note the condition may change in any of these

statements in the while block even though the condition may not be true

as it change execution of the statements continue till the last statement in the block

Therefore it is a good proactice to put the condition changing statement twards the end of the statement block

Note wrong condition 2 i = 0 3 WHILE i <=10 increment i by one – condition chaning print i 11 is also printed to the screen i becomes 11 condition is false but printed trueth is checked at the end of the block

Java code of the second algorithm{ // begining method main int i = 0; // declare and initialize an integer

while( i <10) { // as long as i <=10 do

i = i+1; System.out.printf(“%d\n”,i);

} // end while block} // end method main

Example 4.2 Task: ask the user to enter two integers, the

first one being smaller then the second one, and write the ingegers from the first to the second to the screen

Pseudocode1 Start2 Declare Integer i =0, first, second3a Display “Enter first integer (smaller): “ 3b Input first4a Display “Enter first integer (smaller): “ 4b Input second5 Set i = first6 WHILE i <=second Display i Set i = 1+1 // increment i by one – condition

changing End While7 End

Java code – main block{ Scanner input = new Scanner(System.in); int first, second; // first and second numbers int i; // declare not initilize System.out.printf(“Enter first integer (smaller):”); first = input.nextInt(); System.out.printf(“Enter second integer (larger):”); second= input.nextInt(); i = first; // initialization of the control variable while( i <=second )

{ // as long as i <=second do System.out.printf(“%d\n”,i); i = i+1; // increment – condiiton changing } // end while block} // end method main

Note Note that how many times the action –

printing to screen – is performed is known before the while loop

it is determieed by the two numbers entered by the user

the control variable counter variable i counts this taking values from first number to the second incrementing by one at the end of the

printing

A class of ten students took a quiz. The grades (integers in the range 0 to 100) for this quiz are available to you. Determine the class average on the quiz.

The class average is equal to the sum of the grades divided by the number of students.

The algorithm for solving this problem on a computer must input each grade, keep track of the total of all grades input, perform the averaging calculation and print the result.

Use counter-controlled repetition to input the grades one at a time. A variable called a counter (or control variable) controls the number of

times a set of statements will execute. Counter-controlled repetition is often called definite repetition, because

the number of repetitions is known before the loop begins executing.


A total is a variable used to accumulate the sum of several values.

A counter is a variable used to count. Variables used to store totals are normally initialized to

zero before being used in a program.


Pseudocode

1 Start2 Declare Integer grade, counter, total,

average3a Set counter = 13b Set total = 04 While counter <= 10 Display “Enter grade:” Input grade Set total = total + grade Set counter = counter + 1 End While

Pseudocode (cont.)

5 Set average = total / 106 Display “The average:”, average7 End

Variables What variables

counter – counting studnets from 1 to 10 grade – geting grade of a student total – sum of grades average – total/counter

The action of geting a grade adding this to the total

is the center of the problem how many times it is done is known – 10

controled by a counter variable

A local variable’s declaration must appear before the variable is used in that method.

A local variable cannot be accessed outside the method in which it’s declared.


The program’s output indicates that the sum of the grade values in the sample execution is 846, which, when divided by 10, should yield the floating-point number 84.6.

The result of the calculation total / 10 is the integer 84, because total and 10 are both integers.

Dividing two integers results in integer division—any fractional part of the calculation is truncated (i.e., lost).


In Fig. 3.6, line 21 total = total + grade; // add grade to total

added each grade entered by the user to the total. This simple statement has a potential problem—adding

the integers could result in a value that’s too large to store in an int variable. This is known as arithmetic overflow and causes undefined

behavior, which can lead to unintended results.


The maximum and minimum values that can be stored in an int variable are represented by the constants MIN_VALUE and MAX_VALUE, respectively, which are defined in class Integer.

There are similar constants for the other integral types and for floating-point types.

Each primitive type has a corresponding class type in package java.lang.


Any time a program receives input from the user, various problems might occur. For example,

// input next grade int grade = input.nextInt();

we assume that the user will enter an integer grade in the range 0 to 100. However, the person entering a grade could enter an integer less

than 0, an integer greater than 100, an integer outside the range of values that can be stored in an int variable, a number containing a decimal point or a value containing letters or special symbols that’s not even an integer.


To ensure that inputs are valid, industrial-strength programs must test for all possible erroneous cases.

A program that inputs grades should validate the grades by using range checking to ensure that hey are values from 0 to 100.

You can then ask the user to reenter any value that’s out of range.

If a program requires inputs from a specific set of values (e.g., nonsequential product codes), you can ensure that each input matches a value in the set.


infinite loop int i =0; while (i >=0)

{ printf(“%d\n”,i); i= i+1; // or i +=1; or i++ or ++i }

the case of an infinite loop the condition i<0 is always true – never false

infinite loop – another example int i =0; while (i >=0)

{ printf(“%d\n”,i); // no condition chanig statement }

the case of an infinite loop the condition i<0 is always true

the condition chaning statment is forgotten

Exercise Task: read a positive integer and calculate

sum of ingegers from 1 to that integer and print the result

Algorithm

1 Start2 Get an positive integer: n3 i = 1, sum =0 initialize sum to zere counter

to 14 WHILE i <=n add i to the sumation increment i by one – condition changing 5 Display sum 6 end

Java code – main method{ Scanner input = new Scanner(System.in); int i = 1,sum=0; /* declare and initialize an integer */

Syste.out.printf(“Enter an integer:”); n = input.nextInt(); while(i <= n){ sum = sum + i; i = i + 1; } // end of the while block System.out.printf(“%d\n,sum”);} // end method main

Develop a class-averaging program that processes grades for an arbitrary number of students each time it’s run.

Sentinel-controlled repetition is often called indefinite repetition because the number of repetitions is not known before the loop begins executing.

A special value called a sentinel value (also called a signal value, a dummy value or a flag value) can be used to indicate “end of data entry.”

A sentinel value must be chosen that cannot be confused with an acceptable input value.


Top-down, stepwise refinement Begin with a pseudocode representation of the top—a single

statement that conveys the overall function of the program: Determine the class average for the quiz

The top is a complete representation of a program. Rarely conveys sufficient detail from which to write a Java program.

Divide the top into a series of smaller tasks and list these in the order in which they’ll be performed.

First refinement: Initialize variables

Input, sum and count the quiz gradesCalculate and print the class average

This refinement uses only the sequence structure—the steps listed should execute in order, one after the other.


3.9 Formulating Algorithms with Top-Down, Stepwise Refinement Problem becomes:

Develop a class-averaging program that will process an arbitrary number of grades each time the program is run.

Unknown number of students How will the program know to end?

Use sentinel value Also called signal value, dummy value, or flag value Indicates “end of data entry.” Loop ends when user inputs the sentinel value Sentinel value chosen so it cannot be confused with

a regular input (such as -1 in this case)

3.9 Formulating Algorithms with Top-Down, Stepwise Refinement Top-down, stepwise refinement

Begin with a pseudocode representation of the top:Determine the class average for the quiz

Divide top into smaller tasks and list them in order: Initialize variablesInput, sum and count the quiz gradesCalculate and print the class average

Many programs have three phases: Initialization: initializes the program variables Processing: inputs data values and adjusts program

variables accordingly Termination: calculates and prints the final results

Determine variables

3.9 Formulating Algorithms with Top-Down, Stepwise Refinement Refine the initialization phase from Initialize

variables to:Initialize total to zeroInitialize counter to zero

Refine Input, sum and count the quiz grades to

Input the first grade (possibly the sentinel)While the user has not as yet entered the sentinel Add this grade into the running total Add one to the grade counter Input the next grade (possibly the sentinel)

3.9 Formulating Algorithms with Top-Down, Stepwise Refinement Refine Calculate and print the class average to

If the counter is not equal to zero Set the average to the total divided by the counter Print the averageelse Print “No grades were entered”

What variables are needed average = total / counter – float total - int – acumulate total grades counter – int – count grades grade – int – holds each grade

Every time a new value is entered previous is lost One variable is enough

3.9 Formulating Algorithms with Top-Down, Stepwise Refinement

Initialize total to zeroInitialize counter to zero

Input the first gradeWhile the user has not as yet entered the sentinel

Add this grade into the running totalAdd one to the grade counterInput the next grade (possibly the sentinel)

If the counter is not equal to zeroSet the average to the total divided by the counterPrint the average

elsePrint “No grades were entered”

Second refinement: commit to specific variables. The pseudocode statement

Initialize variables

can be refined as follows:Initialize total to zero

Initialize counter to zero


The pseudocode statementInput, sum and count the quiz grades

requires a repetition to successively input each grade. We do not know in advance how many grades will be

entered, so we’ll use sentinel-controlled repetition. The second refinement of the preceding pseudocode

statement is thenPrompt the user to enter the first gradeInput the first grade (possibly the sentinel)While the user has not yet entered the sentinel

Add this grade into the running totalAdd one to the grade counterPrompt the user to enter the next gradeInput the next grade (possibly the sentinel)


The pseudocode statementCalculate and print the class average

can be refined as follows:If the counter is not equal to zero

Set the average to the total divided by the counterPrint the average

elsePrint “No grades were entered”

Test for the possibility of division by zero—a logic error that, if undetected, would cause the program to fail or produce invalid output.


Program logic for sentinel-controlled repetition Reads the first value before reaching the while. This value determines whether the program’s flow of control

should enter the body of the while. If the condition of the while is false, the user entered the sentinel value, so the body of the while does not execute (i.e., no grades were entered).

If the condition is true, the body begins execution and processes the input.

Then the loop body inputs the next value from the user before the end of the loop.


Most averages are not whole numbers (e.g., 0, –22 and 1024). For this reason, we calculate the class average in this example as a floating-

point number. To perform a floating-point calculation with integers,

temporarily treat these values as floating-point numbers for use in the calculation.

The unary cast operator (double) creates a temporary floating-point copy of its operand.

Cast operator performs explicit conversion (or type casting). The value stored in the operand is unchanged. Java can evaluate only arithmetic expressions in which the

operands’ types are identical. Promotion (or implicit conversion) performed on operands. In an expression containing values of the types int and double, the int values are promoted to double values for use in the expression.


A cast operator is formed by placing parentheses around any type’s name.

The operator is a unary operator (i.e., an operator that takes only one operand).

Java also supports unary versions of the plus (+) and minus (–) operators.

Cast operators associate from right to left; same precedence as other unary operators, such as unary + and unary -.

This precedence is one level higher than that of the multiplicative operators *, / and %.

Appendix A: Operator precedence chart


Floating-Point Number Precision Floating-point numbers are not always 100% precise, but they have numerous applications. For example, when we speak of a “normal” body temperature of 98.6, we do not need to be precise to a large number of digits. When we read the temperature on a thermometer as 98.6, it may actually be 98.5999473210643. Calling this number simply 98.6 is fine for most applications involving body temperatures.


Floating-point numbers often arise as a result of division. In conventional arithmetic, when we divide 10 by 3, the result is

3.3333333…, with the sequence of 3s repeating infinitely. The computer allocates only a fixed amount of space to hold

such a value, so clearly the stored floating-point value can be only an approximation.

Owing to the imprecise nature of floating-point numbers, type double is preferred over type float, because double variables can represent floating-point numbers more accurately.

We primarily use type double throughout the book. In some applications, the precision of float and double

variables will be inadequate. For precise floating-point numbers (such as those required by

monetary calculations), Java provides class BigDecimal (package java.math), which we’ll discuss in Chapter 8.


part of Java code{

Scanner input = new Scanner(System.in);int grade;int count = 0;int total = 0;double average;String more;char cont;

System.out.print("More Grades (y or Y) ?");more = input.next();cont = more.charAt(0);

while(cont == 'y' || cont == 'Y') { System.out.print("Enter grade:");

grade = input.nextInt();//input.nextLine();count++;

total += grade;

System.out.print("More Grades (y or Y) ?");more = input.next();cont = more.charAt(0);

} // end while

if (count == 0)System.out.println("No grades enterd");

else{

average = (double)total / count;System.out.printf("Class average:%10.2f\

n",average);}

} // end method main

More Grades (y or Y) ?yEnter grade:10More Grades (y or Y) ?yEnter grade:20More Grades (y or Y) ?nClass average: 15.00

More Grades (y or Y) ?nNo grades enterd

character type 2 byte storage Unicode characters ‘A’, ‘B’, ‘a’, ‘0’... letters digits more String is a set of characters when the user seesmore grades (y or Y)? expects to enter y or Y and press Enter more = input.next(); reads the charcters until a cpace or end of line and

steore in a Sring variable more

we need the first charcter of the String variable more as a char type

cont = more.charAt(0); cont is a character type aand assigned the first character of Strring more if ( cont == ‘y’ || cont == ‘Y’ ) is checked as the while loops condition Only when the first character of what the

user enters is either ‘Y’ or ‘y’ the program ask to enter a grade

The actions to be repeated are: get a grade add to total increment counter by one then ask wheter more grade or not this is the condition chaning statment in case of entering other then ‘Y’ or ‘y’

iteratgions terminate

Note that in this version no validation chack on grade it can be positive, greater then 100 or

negative any valid integer number is accepted as a

grade

Version 3 with Sentenial Variableint grade = 1;int total = 0;int counter = 0;while ( grade !=-1 ) { // while block print(“Enter grade:”); grade = input.nextInt(); if (grade != -1) { // if block total = total + grade; count = count + 1; } // end of if block} // end of while

if (count == 0 ) println(“average can not be calculated”);else { average = (double)total / count; printf(“average. %10.2f”,average);} // end else} // end method main

Example 4. Task: read numbers from keybord and print

to screen as long as they are greater then zero

Algorithm

1 READ a new number2 WHILE number>= 0 PRINT number READ a new number – conditin chaning3 END the condition has to change in the loop but

twords the end of the loop as much as possible

following algorithm not atchive the talk correctly

1 number is initiliezed to one 2 WHILE number >= 0 READ a new number – condition changing PRINT number 3 END at step 1:

a pseude value for number is given to evalueat the conditon in while

Note at step 1:

a pseude value for number is given to evalueat the conditon in while

the conditon chaning statement is READ a number when the user enters a new numer the number

varible may be positive or negative the conditon is satisfied or not but the chacking is done at he end of the loop if a user enters a negative number it is printed

as well this is an undisirable action

This case study examines nesting one control statement within another.

A college offers a course that prepares students for the state licensing exam for real-estate brokers. Last year, ten of the students who completed this course took the exam. The college wants to know how well its students did on the exam. You’ve been asked to write a program to summarize the results. You’ve been given a list of these 10 students. Next to each name is written a 1 if the student passed the exam or a 2 if the student failed.


This case study examines nesting one control statement within another.

Your program should analyze the results of the exam as follows: Input each test result (i.e., a 1 or a 2). Display the

message “Enter result” on the screen each time the program requests another test result.

Count the number of test results of each type. Display a summary of the test results, indicating

the number of students who passed and the number who failed.

If more than eight students passed the exam, print “Bonus to instructor!”


3.10 Nested control structures Problem

A college has a list of test results (1 = pass, 2 = fail) for 10 students

Write a program that analyzes the results If more than 8 students pass, print "Raise Tuition"

Notice that The program must process 10 test results

Counter-controlled loop will be used Two counters can be used

One for number of passes, one for number of fails Each test result is a number—either a 1 or a 2

If the number is not a 1, we assume that it is a 2

3.10 Nested control structures Top level outline

Analyze exam results and decide if tuition should be raised

First RefinementInitialize variablesInput the ten quiz grades and count passes and failuresPrint a summary of the exam results and decide if

tuition should be raised Refine Initialize variables to

Initialize passes to zeroInitialize failures to zeroInitialize student counter to one

3.10 Nested control structures Refine Input the ten quiz grades and count

passes and failures to While student counter is less than or equal to ten

Input the next exam resultIf the student passed Add one to passeselse Add one to failuresAdd one to student counter

Refine Print a summary of the exam results and decide if tuition should be raised to

Print the number of passesPrint the number of failuresIf more than eight students passed

Print “Raise tuition”

3.10 Nested control structures

Initialize passes to zeroInitialize failures to zeroInitialize student to one

While student counter is less than or equal to tenInput the next exam result

If the student passedAdd one to passes

else

Add one to failures

Add one to student counter

Print the number of passes

Print the number of failures

If more than eight students passed

Print “Raise tuition”

Example: Area of a Circle calculate the area of a circule 1 Start 2 enter a radius 3 WHILE the radius is less then zero enter a radius 4 calculate area area = 3.14*radius*radius 5 print area 6 end

Java code

Scammer input = new Scanner(System.in); double radius, area; System.out.printf(“enter a radius: radius>=0”); radius= input.nextDouble(); while (radius < 0) { System.out.printf(“enter a radius: radius >=0”); radius= input.nextDouble(); // reenter radius until it

is greater then zero } // end of while block area = 3.14*radius*radius; System.out.printf(“area: %10.2f\n”,area );

Notes before calculating the area, radius must be

a positive number ask repeatedly until a valid radius is entered before evaluating the condition a value for

radius must be known As long as the radius is less then zero

asked to the user repeatetly

Another version of the codedouble radius = -1.0, area;// initial value of radius is less then zere the

program enters // while ot least onece and ask a new radiuswhile (radius<0) { printf(“enter a radius: radius>=0”);Radius=input.nextDouble(); // reenter radius // until it is greater then

zero } // end of while block area = 3.14*radius*radius; printf(“area: %f\n”,area );

Example: Calculating the area of a circle modify the previous program enabling the

user to enter new radius values for calculating the area of new circles until a stoping criteria is entered

Example: Calculating the area of a circle Top down design of the algorithm While the user wants to enter another radius

ask a valid radius to the user and calculate the print area of a circle

ask the user whether continue or not the outer loop performs a area calculation at

and ask the user to calcuate another area by a contro variable initial value is always true so at least a calculation

is done condtion may change at the end of the iteration

Part of JavaCode double radius, area; int cont =1; // control variable while (cont ==1) { radius = -1.0; while (radius<0) { printf(“enter a radius: radius>=0”); radius = input.nextDouble(); } // end of while block chaking negative radius values area = 3.14*radius*radius printf(“area: %f\n”, ); printf(“do you want to enter another radius 1: yes,2

no”); cont = nextınt(); } // end of outer while checking another area calculation

Notes the inner while checks whether the radius is

positive then calculate and print the area the outer while checks whether the user

wants to enter another radius or not using a control variable – cont: 1 continue, other

values not ask a question as the last statement

Example: Forex conversion Forex conversion program revisited the user has some TL wants to convert to dollar Euro or pound ask repeatetly until a the user wnts to stop

enters 0 to end the program otherwise the program enables to aak another

value

Algorithm Start Define exchange rates for

dollar, Euro and Pound Ask the user to enter her choice by

presenting a menu While the user wants to continue

ask TL convert TL to forex print the resutls ask user for another conversion

end

Algorithm Convert TL to forex can be detailed as:

if the user chooses dollar convert to dollar and print the result

if the user chooses Euro convert to Euro and print the result

if the user chooses Pounds convert to Pounds and print the result

Part of the Java code double tl,value; double fxDol=1.35,fxEu =1.75,fxPo=2.5; int cont; printf(“1: dollar\n2: Euro\ 3: Pound\0:exit\

n); Cont= input.nextInt();

while (cont !=0) { printf(“enter tl:”); tlinput.nextDouble();

if (cont == 1) { value = tl/fxDol; printf(“dollar :%f\n”,value); }

else if (cont == 2) { value = tl/fxEu; printf(“euro:%f\n”,value); }

else if (cont == 3) { value = tl/fxPo printf(“pound:%f\n”,value); } else { printf(“”You entered a wrong number\n”); }

printf(“1: dollar\n2: Euro\ 3: Pound\0:exit\n);

cont= input.nextInt(); } // end of while block

} // end of main block

Notes Before entering while ask a choice if it is 0 not

enter while in the whlle block

ask a tl amount to purchase forex make the calculations print the amount of forex that can be purchased At the end of the while block ask agaşb a choice to the

user if it is zero condition is checked and not enter while if not repeat action

The same variable is used for both as a control whether continue or not 0 choosing the forex type 1,2,3 any other characeter indicating no more calculations

Compound assignment operators abbreviate assignment expressions.

Statements likevariable = variable operator expression;

where operator is one of the binary operators +, -, *, / or % can be written in the form

variable operator= expression; Example:

c = c + 3;can be written with the addition compound assignment operator, +=, as

c += 3; The += operator adds the value of the expression on its right to

the value of the variable on its left and stores the result in the variable on the left of the operator.


Unary increment operator, ++, adds one to its operand Unary decrement operator, --, subtracts one from its

operand An increment or decrement operator that’s prefixed to

(placed before) a variable is referred to as the prefix increment or prefix decrement operator, respectively.

An increment or decrement operator that’s postfixed to (placed after) a variable is referred to as the postfix increment or postfix decrement operator, respectively.


Using the prefix increment (or decrement) operator to add 1 to (or subtract from) a variable is known as preincrementing (or predecrementing).

This causes the variable to be incremented (decremented) by 1; then the new value is used in the expression in which it appears.

Using the postfix increment (or decrement) operator to add 1 to (or subtract 1 from) a variable is known as postincrementing (or postdecrementing).

This causes the current value of the variable to be used in the expression in which it appears; then the variable’s value is incremented (decremented) by 1.


Appendix D lists the eight primitive types in Java. Java requires all variables to have a type. Java is a strongly typed language. Primitive types in Java are portable across all

platforms. Instance variables of types char, byte, short, int, long, float and double are all given the value 0 by default. Instance variables of type boolean are given the value false by default.

Reference-type instance variables are initialized by default to the value null.


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