Java Programming - Classes and Objects

What are the four numbers outputted? public class QuizClass { public static int num1; public int num2; ... public static void main(String [] args) { QuizClass a = new QuizClass(); QuizClass b = new QuizClass(); a.num1 = 1; a.num2 = 2; b.num1 = 3; b.num2 = 4; System.out.println(a.num1 + " " + a.num2 + " " + b.num1 + " " + b.num2); } }

3, 2, 3, 4 since num1 is static and will be the same for all instances

How many objects of type A will be created? pubic class A{ public A friend; public A(){ friend = null; } public A (A other){ friend = newA(other.friend); } public void setFriend(A newFriend){ friend = newFriend; } A firstVar = new A(); firstVar.setFriend(new A()); A secondVar = new A(firstVar); }

4

What will this output? Person[] people = new Person[3]; people[0] = new Person("Bob"); people[1] = new Person("Alice"); people[2] = new Person("Jane"); // make a copy Person[] peopleCopy = new Person[3]; for (int i = 0; i < 3; i++){ peopleCopy[i] = people[i]; } // now I can change some names people[2].setName("Jane Doe"); people[0] = new Person("Michelle"); System.out.println(peopleCopy[0] + ":" + peopleCopy[1] + ":" + peopleCopy[2]);

Bob:Alice:Jane Doe

an object is

an instance of the class

Instance members must be associated with ___

an object

blueprint from which individual objects are created

class

static member variables and static member methods are sometimes called ___ variables and methods

class

class variables and methods belong to the ____ itself rather than to ____ of that class

class instances

class is visible to all classes everywhere

class declared with the modifier "public"

class only visible within its own package

class has no modifier (package-private)

To return a string with an object, you would...

create toString method

What does this code do? String [] names = new String[20];

creates an array of 20 strings

declaring a variable (does/does not) create an object

does not

immutable means

does not change

If an equals method has not been implemented, what will this code output? (assume class is called Car and constructor for make of the car has been implemented) Car firstCar = new Car("Dodge"); Car secondCar = new Car("Dodge"); System.out.println(firstCar.equals(secondCar));

false because the default equals method checks the memory location

example of? static final double PI = 3.141592653589793;

final modifier

the value of this field cannot change

final modifier

accessor methods are referred to as?

getter methods

JUnit testing should be applied to

individual methods

example of? class MountainBike extends Bicycle{ //new fields and methods defining the subclass MountainBike }

inheritance

What does the second line of code do? PairOfDice dice; //declares a variable of type PairOfDice dice = new PairOfDice();

initializes the object's instance variables and returns a reference to the object

An object created from a class is called an ______ of that class

instance

PlayerData class creates an object. that object is an ____ of the PlayerData class. name and age are ____ _____ in the object.

instance instance variables

methods that the object contains

instance methods

variables that the object contains

instance variables

public ____ getArea() { return width * height; }

int

What are the parameters of the constructor? public class PairOfDice { public int die1; public int die2; public PairOfDice(int val1, int val2){ die1 = val1; die2 = val2; } public void roll(){ die1 = (int)(Math.random()*6) + 1; die2 = (int)(Math.random()*6) + 1; } }

int val1, int val2

subroutine

method

instance variable declared private is not visible from...

methods within other classes

setter method is also referred to as?

mutator method

Objects are created with what operator?

new

Can a constructor be declared static?

no

can a constructor return void?

no

Correct? public void myMethod(){ int x; if (x>10) { System.out.println("larger than 10"); } }

no because x was never initialized

Does the code below create a new object? public Date (Date oldDate) { this(oldDate.getDay(), oldDate.getMonth(); oldDate.getYear(); } assume Date method is defined earlier in code

no, because it is a copy constructor that sets the values of the current object being created

Will this return a String of the date? Date taxDay = new Date(15, "April", 2016); System.out.println("Tay day is " + taxDay);

no, it will print the location in memory where the object taxDay is stored

Correct? public class QuizClass{ int num; String text; public static void printNice() { System.out.println(text + " " + num); } }

no, text and num are not intialized

what is an actual value stored in the variable?

null

a namespace that organizes a set of related classes and interfaces

package

when a method takes in something

parameter

To make data not seen outside the class, you declare it as ___

private

T/F arrays cannot contain primitive types

F

T/F default constructor is generated by the compiler even when another constructor defined in the class

F

T/F if a class is immutable, it needs setters

F

T/F static members can be associated with any specific instance of the class

F

T/F private variables can be seen in methods from other classes

F

T/F static variables can only be used in static methods

F

T/F boxing is the automatic conversion of a private variable to a wrapper class

F, it is the automatic conversion of a primitive type to the corresponding wrapper class

T/F a constructor can assign a value to a constant (variable defined final) with all variables

F, only for class variables. not variables defined within the constructor or within already created objects

If a class is immutable, is it necessary to perform a deep copy in the copy constructor?

No

Does this code print out the line? Date taxDay = new Date915, "April", 2016); Date alsoTaxDay = new Date(15, "April", 2016); if (taxDay.equals(alsoTaxDay)){ System.out.println("They are the same"); }

No, because the default equals method does not check the value, it checks if the two live at the same memory location

Correct? ArrayList<char> lalaString = new ArrayList<char>();

No, primitive types cannot be stored in array list. Should be character instead

Correct? public class Point { public int x; public int y; public Point(){ x = y = 0; } public static int getX(){ return x; } public static int getY(){ return y; }

No, static methods cannot access class members

A class that is not explicitly a subclass is automatically a subclass of what class?

Object

What class is not a subclass of any other class?

Object

public class PairOfDice { public int die1; public int die2; public _______(int val1, int val2){ die1 = val1; die2 = val2; }

PairOfDice

T/F ArrayLists can contain other ArrayLists

T

T/F arrays can contain ArrayLists

T

T/F arrays can contain other arrays

T

T/F encapsulation restricts access to data within a class

T

T/F if there is no constructor defined, the compiler generates a default constructor

T

T/F it is okay to have two constructors with the same name but different parameters

T

T/F the default equals method checks memory location

T

T/F you can make a class immutable by setting the variables to final

T

T/F Encapsulation controls access to variables (ie private vs public) using getters and setters

T

T/F Every class is a subclass of another class

T

T/F a constructor will control how the instance variables are initialized

T

How is the class variable different from the instance variable below? public class Bicycle { private int cadence; private int gear; private int speed; //add inst var for the obj ID private int ID: //add class var for # Bicycle obs instantiated private static int numberOfBicycles = 0; ... }

The class variable is not related to any individual object, but to the class as a whole. It is related to all Bicycle objects. the ID number instance variable is related to one specific individual object.

How would you encapsulate data?

Through getter and setter methods

Correct? public class QuizClass { public int x; public static String text; public int square (int x) { return x * x; } public String getName() { return text; } }

Yes

Can the parameter-list for a constructor be empty?

Yes if the constructor has no parameters

Correct? public class Point{ public final int x; public final int y; public Point(int newx, int newy){ x = newx; y = newy; } }

Yes, a constructor can assign value to a final/constant

Correct? public boolean equals(Date otherDate){ if (day == otherDate.getDay() && month.equals(otherDate.getMonth()) && year == otherDate.getYear()){ return true; } else{ return false; } }

Yes, use .equals to compare Strings and use == to compare integers

What is PairOfDice()? PairOfDice dice; //declares a variable of type PairOfDice dice = new PairOfDice();

a constructor

a variable holds the object, or a reference to an object?

a reference to an object

a void method does not need to contain?

a return statement

After executed, what does "dice" refer to? PairOfDice dice; //declares a variable of type PairOfDice dice = new PairOfDice();

the newly created object

'this' keyword refers to what?

the object being created

In a JUnit test, what does the code below expect? assertFalse(myMethod(5, 15));

the output of the method to be false and triggers an error otherwise

what must be the name of the constructor?

the same name of the class in which it is defined

you can define constants with?

the static modifier and the final modifier

a reference to the current object

this

What modifiers can be used on a constructor definition?

three access modifiers: public, private, and protected

The statement below is an example of int x = new Integer(5);

unboxing

make variables common to all objects

use the static modifier

method declared ____ does not return a value

void

Are strings objects?

yes

Can a constructor have a list of formal parameters?

yes

correct? if (std == null)

yes

change using 'this' public class Point{ public int x = 0; public int y = 0; //constructor public Point(int a, int b){ x = a; y = b; } }

public class Point{ public int x = 0; public int y = 0; //constructor public Point(int x, int y){ this.x = x; this.y = y; } }

a constructor has no __ type

return

when asking the user for something

scanner

the java class library is a?

set of packages

public void setTitle(String newTitle){ title = newTitle; }

setter method

two characteristics of objects

state and behavior