AP Computer Science A Void

What is an instance method?

• An instance method is a piece of code called on a specific instance (an object) of the class.

• An instance method is a piece of code that does not depend on any specific instances (objects), just on the general class.

• An instance method adds functionality to a class by creating private fields.

• An instance method adds functionality to the class by printing out a result.

Which of the following is a correctly written method for the class below?

public class Timer

{

private int startMin;

private int length;

public Timer(int minute, int duration)

{

startMin = minute;

length = duration;

}

public Timer(int duration)

{

startMin = 0;

length = duration;

}

}

• public void addFiveMinutes()

  {

  length = length + 5;

  }

• public addFiveMinutes()

  {

  length = length + 5;

  }

• addFiveMinutes()

  {

  length = length + 5;

  }

• public void addFiveMinutes

  {

  length = length + 5;

  }

Which of the following correctly calls the method addFiveMinutes on an object of the Timer class called kitchenTimer?

• kitchenTimer(addFiveMinutes)

• Timer.addFiveMinutes()

• kitchenTimer.addFiveMinutes()

• kitchenTimer.addFiveMinutes

  Answered

Suppose the class Timer has a method called startTime that prints out the starting time of the Timer.

Which of the following correctly uses this method to print out the start time of a Timer object called laundry?

• System.out.println(laundry.startTime());

• System.out.println(laundry.startTime);

• int start = laundry.startTime();

• laundry.startTime();

A Timer class is a class that represents a minute timer. A partial definition of the class is given below.

public class Timer

{

private int length;

public Timer(int duration)

{

length = duration;

}

public void endTime()

{

System.out.print("The timer will end in " );

System.out.print(length);

System.out.println(" minutes");

}

public void addFiveMinutes()

{

length = length + 5;

}

}

What is the output of the following main method?

public static void main(String[] args){

Timer muffins = new Timer(30);

muffins.endTime();

muffins.addFiveMinutes();

muffins.endTime();

}

• The timer will end in 30 minutes

• The timer will end in 30 minutes

  The timer will end in 35 minutes

• The timer will end in 30 minutes

  The timer will end in 30 minutes

• This method won’t print anything because it doesn’t have any print statements.