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System.out.println("Enter the phone age in years:");

outputs "Enter the phone age in years" for user to respond to

We prompt the user to enter the phone age in years.

int phoneAge = scan.nextInt();

defines a new int as the input from the user

We read the phone age by calling the nextInt() method because this input is an integer.

int phoneAge = scan.nextInt();

defines a new int as the input from the user

We need to read the phone age that the user enters and store it in a variable.

System.out.println("Enter whether the phone is broken (true or false):");

Asks user a true or false question

We prompt the user to enter whether the phone is broken.

boolean isBroken = scan.nextBoolean();

creates a boolean variable defined by the user input

We need to read whether the phone is broken and store it in a variable.

boolean isBroken = scan.nextBoolean();

creates a boolean variable defined by the user input

The variable isBroken is true when the phone is broken, and false otherwise.

boolean isBroken = scan.nextBoolean();

creates a boolean variable defined by the user input

We read whether the phone is broken by calling the nextBoolean() method because this input is a boolean.

scan.close();

ends input capability

We close the scanner as we do not want to process any input from the user in the rest of the program.

Scanner scan = new Scanner(System.in);

Data entry

To read the input values from the user, we need to define a Scanner object.

Scanner scan = new Scanner(System.in);

Data entry

We need to read and process the values that the user enters.

System.out.println("Enter the phone age in years:");

On-screen display "Enter the phone age in years:"

We prompt the user to enter the phone age in years.

int phoneAge = scan.nextInt();

Telphone age entry

We read the phone age by calling the nextInt() method because this input is an integer.

int phoneAge = scan.nextInt();

Telphone age entry

We need to read the phone age that the user enters and store it in a variable.

System.out.println("Enter whether the phone is broken (true or false):");

Shows the phrase: "Enter whether the phone is broken (true or false):"

We prompt the user to enter whether the phone is broken.

boolean isBroken = scan.nextBoolean();

Whether it is broken or not

We need to read whether the phone is broken and store it in a variable.

boolean isBroken = scan.nextBoolean();

Whether it is broken or not

The variable isBroken is true when the phone is broken, and false otherwise.

boolean isBroken = scan.nextBoolean();

Whether it is broken or not

We read whether the phone is broken by calling the nextBoolean() method because this input is a boolean.

scan.close();

Closes entries

We close the scanner as we do not want to process any input from the user in the rest of the program.

boolean needPhone = isBroken || phoneAge >= 3;

determines a boolean (T/F) based on what the user inputted or if the phoneAge value is greater than or equal to 3

We use the || operator (called or) to combine the two conditions.

boolean needPhone = isBroken || phoneAge >= 3;

determines a boolean (T/F) based on what the user inputted or if the phoneAge value is greater than or equal to 3

The first condition is to test if the phone is broken and the second condition is to test if the phone age is at least 3 years old.

boolean needPhone = isBroken || phoneAge >= 3;

determines a boolean (T/F) based on what the user inputted or if the phoneAge value is greater than or equal to 3

We need two conditions to determine if it is the time for a new phone.

boolean needPhone = isBroken || phoneAge >= 3;

Conditions if a new phone is needed

We use the || operator (called or) to combine the two conditions.

boolean needPhone = isBroken || phoneAge >= 3;

Conditions if a new phone is needed

The first condition is to test if the phone is broken and the second condition is to test if the phone age is at least 3 years old.

boolean needPhone = isBroken || phoneAge >= 3;

Conditions if a new phone is needed

We need two conditions to determine if it is the time for a new phone.

System.out.println(needPhone);

Shows whether it is necessary or not

This statement prints true/false depending on whether it is time to buy a new phone.

System.out.println(needPhone);

Shows whether it is necessary or not

The printed value is followed by an end-of-line character in the end.

System.out.println(needPhone);

outputs the boolean result of "needPhone"

This statement prints true/false depending on whether it is time to buy a new phone.

System.out.println(needPhone);

outputs the boolean result of "needPhone"

The printed value is followed by an end-of-line character in the end.

String fullName = "John Smith"

Stores the name

We define a string variable to hold the name.

String firstInitial = fullName.substring(0, 1);

Retrieves the initial of the first name

We need to extract the first letter from the first name.

String firstInitial = fullName.substring(0, 1);

Retrieves the initial of the first name

We do this by calling the substring(0,1) method.

String lastInitial = fullName.substring(5, 6);

Retrieves the initial of the least name

We need to extract the first letter from the last name.

String lastInitial = fullName.substring(5, 6);

Retrieves the initial of the least name

We do this by calling the substring(5,6) method.

String initials = firstInitial + lastInitial;

Join the two initials

This statements concatenates the extracted initials and store the result in the string initials.

System.out.println(initials);

Shows initials

This statement prints the initials to the default standard output stream.

System.out.println(initials);

Shows initials

The printed value is followed by the end-of-line character at the end.

int[] values = {5, 8, 4, 78, 95, 12, 1, 0, 6, 35, 46};

Values to be analyzed

We define array values to hold the specified numbers.

int[] values = {5, 8, 4, 78, 95, 12, 1, 0, 6, 35, 46};

Values to be analyzed

We initialize the array by separating elements with a comma and enclosing the collection in braces { }.

int maxValue = values[0];

Variable that will store the maximum value

We need variable maxValue to store the maximum value of the array.

int maxValue = values[0];

Variable that will store the maximum value

We initialize this variable by the first value in the array because we initially assume that the first value is the maximum.

for (int i = 1; i < values.length; i++) {

Loop start

We use a for loop to iterate over the remaining array indexes and search for the maximum value.

for (int i = 1; i < values.length; i++) {

Loop start

We need the array indexes to start at 1 with every integer number up to but not including the array length.

if (values[i] > maxValue) {

First condition

We need to compare the value at the index i of the array with the maximum value stored in variable maxValue.

if (values[i] > maxValue) {

First condition

If the value at that index is larger than the maximum value, then we need to set the maximum value to the value of the element at index i.

System.out.println("Maximum value: " + maxValue);

Prints the result

This statement prints the maximum value of the array to the default standard output stream.

maxValue = values[i];

Recovers the maximum value

This statement sets the maximum value to value of the element at index i of the array.

for (int num = 2; num <= 10; num += 2) {

Loop structure

To do this, we need to use a loop structure.

for (int num = 2; num <= 10; num += 2) {

Loop structure

We need to repeat the same process for each of the even positive integers that are less than or equal to 10.

for (int num = 2; num <= 10; num += 2) {

Loop structure

To do this, we initialize variable num to 2, loop until reaching 10 (inclusive), and increment num by 2 after each iteration of the loop.

for (int num = 2; num <= 10; num += 2) {

Loop structure

We use for loops instead of a while loop because we need to repeat the loop a certain number of times, and for loops are best-suited in cases like this when we know ahead of time the number of times that we need to repeat the loop.

for (int num = 2; num <= 10; num += 2) {

Loop structure

Here, we want the for loop to start counting from 2 (2 is the first positive even number) with every even integer number up to (including) 10.

System.out.println(num + " squared = " + (num * num));

Prints the result

The multiplication may also be performed directly in the println statement.

System.out.println(num + " squared = " + (num * num));

Prints the result

Note that we do not necessarily have to store the squared number in a variable.

System.out.println(num + " squared = " + (num * num));

Prints the result

To square each number in the sequence, we multiply it by itself using the multiplication (*) operator.

System.out.println(num + " squared = " + (num * num));

Prints the result

In each iteration of the loop, this statement prints the square number to the default standard output stream.

Point1 point = new Point1();

Stores the point

This statement creates a Point1 object using the new keyword and empty parentheses.

Point1 point = new Point1();

Stores the point

The variable point holds a reference to a Point1 object.

point.setX(7);

Set the X axis

This statement invokes the method setX of the point to set its x-coordinate to 7.

point.translate(11, 6);

Joins the x and y axis values

This statement invokes the method translate of the point.

point.translate(11, 6);

Joins the x and y axis values

The second parameter specifies how much we want to shift the y-coordinate of the point.

point.translate(11, 6);

Joins the x and y axis values

The translate method receives two parameters.

point.translate(11, 6);

Joins the x and y axis values

The first parameter specifies how much we want to shift the x-coordinate of the point.

System.out.println("The point's coordinates: (" + point.getX() + ", " + point.getY() + ")") ;

Prints the axes

Note that we do not necessarily have to store the returned value from each of these methods in a variable.

System.out.println("The point's coordinates: (" + point.getX() + ", " + point.getY() + ")") ;

Prints the axes

We could use the returned value of them directly in the println statement.

System.out.println("The point's coordinates: (" + point.getX() + ", " + point.getY() + ")") ;

Prints the axes

This statement prints the coordinates of the point to the default standard output stream.

System.out.println("The point's coordinates: (" + point.getX() + ", " + point.getY() + ")") ;

Prints the axes

The printed text is followed by the end-of-line character at the end.

System.out.println("The point's coordinates: (" + point.getX() + ", " + point.getY() + ")") ;

Prints the axes

To get the point's coordinates, we invoke the method getX and getY of the point.

class Point1 {

Creates the Point1 class

We define the class Point1 to represent a point in the Euclidean plane.

private int y;

Variable Y

Therefore, we need to declare an instance variable for the class to store the y-coordinate of the point.

private int y;

Variable Y

We declare it as integer because we want to have integer coordinates for the point.

private int y;

Variable Y

Note that an instance variable is a variable defined in a class, for which each instantiated object of the class has a separate copy, or instance.

private int y;

Variable Y

Every object of the Point1 class will have its own y-coordinate.

public void translate(int dx, int dy) {

Axles

This method shifts the coordinates by a specific delta-x and delta-y, which are passed as parameters.

public void translate(int dx, int dy) {

Axles

We define this method as public to provide access to this method from outside of the class.

public void translate(int dx, int dy) {

Axles

Also, we define its return type as void, as it does not return any value.

public void translate(int dx, int dy) {

Axles

Note that both of the parameters are declared as integers because the point has integer coordinates.

x += dx;

Changes the X axis

To shift the x-coordinate of the point, we need to add dx to the value of the x-coordinate of the point.

public void setX(int newX) {

New X axis

Also, we define its return type as void, as it does not return any value.

public void setX(int newX) {

New X axis

We define this method as public to provide access to this method from outside of the class.

public void setX(int newX) {

New X axis

This method sets the current value of the x-coordinate of the point to the given value (newX) that is specified as the method's parameter.

public void setX(int newX) {

New X axis

Note that the instance variable x is private; thus, it cannot be directly changed from outside the class.

public void setX(int newX) {

New X axis

The parameter of the method is declared as integer because the x-coordinate of the point is an integer.

public void setX(int newX) {

New X axis

It can be changed from outside the class only through this method.

public int getX() {

Recovers the X axis

We define this method as public to provide access to this method from outside of the class.

public int getX() {

Recovers the X axis

This method returns the x-coordinate of the point.

public int getX() {

Recovers the X axis

Note that the instance variable x is private; thus, it cannot be directly accessed from outside the class.

public int getX() {

Recovers the X axis

Also, we define its return type as int, as it returns the x-coordinate of the point which is an integer.

public int getX() {

Recovers the X axis

It can be accessed from outside the class only through this getter method.

Scanner scan = new Scanner(System.in);

Set input

To read the input value from the user, we need to define a Scanner object.

Scanner scan = new Scanner(System.in);

Set input

We need to read and process the value that the user enters.

System.out.println("Enter an integer for seconds: ");

Display the message "Enter an integer for seconds:"

We prompt the user to enter the seconds.

int seconds = scan.nextInt();

Creates the variable seconds

We need to read the seconds that the user enters and store it in a variable.

int seconds = scan.nextInt();

Creates the variable seconds

We read the seconds by calling the nextInt() method because this input is an integer.

for (int num = 2; num <= 10; num += 2) {

This for loop will first assign the num variable to 2, execute what is in the body and then increment num by 2 (which guarantees that num is positive) each round until num reaches the value 10.

To do this, we need to use a loop structure.

for (int num = 2; num <= 10; num += 2) {

This for loop will first assign the num variable to 2, execute what is in the body and then increment num by 2 (which guarantees that num is positive) each round until num reaches the value 10.

We need to repeat the same process for each of the even positive integers that are less than or equal to 10.

for (int num = 2; num <= 10; num += 2) {

This for loop will first assign the num variable to 2, execute what is in the body and then increment num by 2 (which guarantees that num is positive) each round until num reaches the value 10.

To do this, we initialize variable num to 2, loop until reaching 10 (inclusive), and increment num by 2 after each iteration of the loop.

for (int num = 2; num <= 10; num += 2) {

This for loop will first assign the num variable to 2, execute what is in the body and then increment num by 2 (which guarantees that num is positive) each round until num reaches the value 10.

We use for loops instead of a while loop because we need to repeat the loop a certain number of times, and for loops are best-suited in cases like this when we know ahead of time the number of times that we need to repeat the loop.

for (int num = 2; num <= 10; num += 2) {

This for loop will first assign the num variable to 2, execute what is in the body and then increment num by 2 (which guarantees that num is positive) each round until num reaches the value 10.

Here, we want the for loop to start counting from 2 (2 is the first positive even number) with every even integer number up to (including) 10.

for (int num = 2; num <= 10; num += 2) {

Since num must be <= 10 to execute what code is in the body of the function, the code in the body will execute for num = 10 as well.

To do this, we need to use a loop structure.

for (int num = 2; num <= 10; num += 2) {

Since num must be <= 10 to execute what code is in the body of the function, the code in the body will execute for num = 10 as well.

We need to repeat the same process for each of the even positive integers that are less than or equal to 10.