Cis 231

Front 1

What is the difference between a class and an object?

Back 1

A class is a blueprint for an object of variables and behaviors. An object is a real set of variables and behaviors stored in the RAM.

Front 2

What is the purpose of a constructor? How is a constructor different from other methods? What happens when a constructor is called

Back 2

A constructor is used to initialize an object. It's different because it needs the same name as the class and does not have a return type. Memory is allocated in the RAM for the object when called.

Front 3

MyTestmt;MyTestmt = new MyTest ();How is line 1 different from like 2? What does line 1 and line 2 achieve?

Back 3

Line 1 calls the object, line 2 creates an object , thus saving a place in the RAM for it. MyTestmt in line 1 = null,Line 2 initializes and contains the address of the object.

Front 4

How is a variable in a method or function different from a global variable? Consider the initial values. What happens when a global and local variable have the same name

Back 4

A variable in a method or function is local, it's only available in that method. A global variable is available to the entire class. If they have the same name, the global variable is used. If it's in a method, the local variable will be used unless you use the this.variable syntax to call the global variable. Instance/global variables have a default value, local do not.

Front 5

How is a variable storing a primitive data type different from a variable holding a reference for an object of a class?

Back 5

Primitive stores the actual value of the data, reference stores a reference of the memory location.

Front 6

How is storing an array different from storing a primitive data type?

Back 6

Arrays are an object, are stored in a location. The address is stored as a reference.Primitive stores the actual value.

Front 7

What is the difference between passing variable by value and passing variable values by reference?

Back 7

Passing by value means a copy of the value is being passed.Pass by reference is an address of the variable being passed.

Front 8

Why are arrays and objects always passed by reference?

Back 8

Arrays and objects are passed by reference because it's easier and the size is unknown.Primitive data types have a known size.

Front 9

Explain the difference between shallow and deep copies of an object?

Back 9

A shallow copy is only a copy of the reference, any changes made will be reflected in the original object.A deep copy of object is the same state and values stored in different locations, you can safely change a value without it reflecting upon the original object.

Front 10

What is an instance variable?

Back 10

A variable declared inside a class, but outside a method.

Front 11

What is a static variable?

Back 11

A class only has one of a static variable, it's value is reserved, even out of scope. It is self contained and belongs to the class, not the object.Can be called without creating an object. Static methods can only use other static variables!

Front 12

What is a static method and how is a static method different from other methods?

Back 12

A method that belongs to a class rather than an instance of a class. It is accessible to every instance of a class, but methods defined in an instance are only able tobe accessed by that member.

Front 13

What do we mean by scope?

Back 13

Defines section of code in which variable is visible. A set of curly braces defines a scope {}.

Front 14

Scope of instance variable?

Back 14

In the class bit outside method.

Front 15

Scope of static variable?

Back 15

The entire class, almost like a global variable.

Front 16

Scope of local variable?

Back 16

Within it's method or function.

Front 17

public int intx (int x){

return x++;

}

Back 17

Yes, it is self contained and can be static.

Front 18

public int getX(){

return x;

}

Back 18

No, it needs to retrieve x so it's not self contained and cannot be static.

Front 19

public int setX (int value){

x = value;

}

Back 19

No, setting an instance variable.

Front 20

public double sqRoot (double y){

logic

let's say sqr=sqRoot;

}

return sqr;

}

Back 20

Yes, self contained, can be static.

Front 21

public int [ ] sort(int [ ] data){

logic for sorting

return sorted

}

Back 21

Yes, self contained, can be static.

Front 22

public double getArea (){

return length *width;

}

Back 22

No, instance variables need to be retrieved, cannot be static.

Front 23

public double salary (Employee emp){return emp.hours * emp.hourlyPay;

}

Back 23

Yes, self contained, playing with object variables, can be made static.

Front 24

Back 24

Front 25

Back 25

Limited in scope

Front 26

Back 26

Front 27

Constructors are a special kind of method that are invoked to

Back 27

construct objects

Front 28

A constructor with no parameters is referred to as a

Back 28

no-arg constructor;

Front 29

a default constructor, is provided automatically only if

Back 29

no constructors are explicitly defined in the class.;

Front 30

To reference an object, ---

Back 30

assign the object to a reference variable.

Front 31

To declare a reference variable, use the syntax:

Back 31

ClassName objectRefVar;

Front 32

Referencing the object’s data:

Back 32

objectRefVar.data

Front 33

Invoking the object’s method:

Back 33

objectRefVar.methodName(arguments)

e.g., myCircle.getArea();

Front 34

If a data field of a reference type does not reference any object, the data field holds

Back 34

a special literal value, null. ;

Front 35

Instance variables belong to a

Back 35

specific instance.

Front 36

Instance methods are invoked by

Back 36

an instance of the class.;

Front 37

Static variables are shared by

Back 37

all the instances of the class.

Front 38

Static methods are not tied to

Back 38

a specific object.

Front 39

Static constants are

Back 39

final variables shared by all the instances of the class.;

Front 40

public

Back 40

The class, data, or method is visible to any class in any package.;

Front 41

private

Back 41

The data or methods can be accessed only by the declaring class.;

Front 42

The get and set methods are used to

Back 42

read and modify private properties;

Front 43

The private modifier restricts access to ----, the default modifier restricts access to ----, and the public modifier enables ----. ;

Back 43

within a class, within a package, unrestricted access

Front 44

If the contents of an object cannot be changed once the object is created, the object is called an ----

Back 44

immutable object and its class is called an immutable class.;

Front 45

For a class to be immutable, it must mark all --- and provide ----that would return a reference to a mutable data field object.;

Back 45

data fields private, no mutator methods and no accessor methods.

Front 46

Class abstraction means to ----

Back 46

separate class implementation from the use of the class.;

Front 47

A String object is immutable; its contents ----.

Back 47

cannot be changed

Front 48

A regular expression (abbreviated regex) is a string that ----. Regular expression is a powerful tool for ----. You can use regular expressions for matching, replacing, and splitting strings.;

Back 48

describes a pattern for matching a set of strings, string manipulations.

Front 49

A constructor is used to ----.Unlike properties and methods, a superclass's constructors are ----. They can only be invoked from the ----, using the keyword super. If the keyword super is not explicitly used, the superclass's----.;

Back 49

construct an instance of a class.

-not inherited in the subclass, subclasses' constructors, no-arg constructor is automatically invoked.

Front 50

You must use the keyword super to call the superclass constructor. Invoking a superclass constructor’s name in a ----. Java requires that the statement that uses the keyword super appear ----.;

Back 50

subclass causes a syntax error, first in the constructor.

Front 51

Constructing an instance of a class invokes all the superclasses’ ----. This is known as ----.;

Back 51

constructors along the inheritance chain, constructor chaining.

Front 52

A subclass inherits from a superclass. You can also:

Back 52

Add new properties

Add new methods

Override the methods of the superclass;

Front 53

A subclass inherits methods from ----. Sometimes it is necessary for the subclass to ----. This is referred to as ----.;

Back 53

a superclass, modify the implementation of a method defined in the superclass, method overriding.

Front 54

An instance method can be overridden only if ---. Thus a ----method cannot be overridden, because it is not----. If a method defined in a subclass is private in its superclass, the two methods are ----.;

Back 54

it is accessible, private, accessible outside its own class, completely unrelated.

Front 55

Like an instance method, a ---- method can be inherited. However, a static method cannot be ----. If a static method defined in the superclass is redefined in a subclass, the method defined in the superclass is ----.;

Back 55

static, overridden, hidden.

Front 56

Polymorphism means that a variable of a ----.;

Back 56

supertype can refer to a subtype object.

Front 57

A class defines a ----. A type defined by a subclass is called a ----, and a type defined by its superclass is called a ----. Therefore, you can say that Circle is a subtype of GeometricObject and GeometricObject is a supertype for Circle.;

Back 57

type, subtype, supertype.

Front 58

You have already used the casting operator to convert variables of one primitive type to another. Casting can also be used to ----.;

Back 58

convert an object of one class type to another within an inheritance hierarchy.

Front 59

Explicit casting must be used when ----. This type of casting may not always succeed.;

Back 59

casting an object from a superclass to a subclass.

Front 60

Use the ---- operator to test whether an object is an instance of a class:;

Back 60

instanceof.

Front 61

Why is this code not compiling correctly??

Public static void main (String args []){

C c = new C ();

}}

Class A {

Public A (int x){

Systen.out.println ("Hello from A's overloaded constructor.");

}}

Class B extends A { }

Class C extends B { }

Back 61

I dunno lol

Front 62

If a method overloads another method, these two methods must have the same exactsignature

Back 62

False

Front 63

A method can be overloaded in the same class

Back 63

True

Front 64

A method can be overridden in the same class

Back 64

False

Front 65

It is a compilation error if overloaded methods differ only in return type

Back 65

True, arguments must differ

Front 66

A method in a subclass can overload a method in the superclass

Back 66

True

Front 67

A subclass is usually extended to contain more functions and more detailed informationthan its superclass

Back 67

True

Front 68

"class A extends B" means A is a subclass of B

Back 68

True

Front 69

Class B is a subclass of A so it is ok to use B b=new A ()

Back 69

True

Front 70

A sub-class reference type can be assigned to a super class object without casting

Back 70

False

Front 71

Method behavior must strictly bind with its name at the compile time always

Back 71

False

Front 72

All classes have a toString() method

Back 72

True

Front 73

All Classes have a common superclass.

Back 73

True

Front 74

If a method is overridden in a subclass, there is no way we can call its superclass version

Back 74

False

Front 75

Static binding means matching method signatures.

Back 75

True

Front 76

Dynamic binding happens at run time.

Back 76

False

Front 77

Bb

Back 77

X