CH.9 QUIZ QUESTIONS – Flashcards
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A constructor can access __________.
- a local variable defined in any method
- a private instance variable
- a public instance variable
- a static variable
answer
- a private instance variable
- a public instance variable
- a static variable
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A method that is associated with an individual object is called ____________.
- a static method
- a class method
- an instance method
- an object method
answer
an instance method
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A static data field can be accessed from any method in the same class.
True or false?
answer
True
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A static method in a class can access the class variables in the same class?
True or false?
answer
True
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A static method in a class can access the instance variables in the same class?
True or false?
answer
False
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All data fields in an object have default values
True or false?
answer
True
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An immutable class cannot have ____________
- public data fields
- private data fields
- public constructors
- no-arg constructors
- static data fields
answer
public data fields
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An object is an instance of a _________.
-program
-class
-method
-data
answer
Class
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Analyze the following code and choose the best answer:
public class Foo {
private int x;
public static void main(String[] args) {
Foo foo = new Foo();
System.out.println(foo.x);
}
}
A-Since x is private, it cannot be accessed from an object foo.
B-Since x is defined in the class Foo, it can be accessed by any method inside the class without using an object. You can write the code to access x without creating an object such as foo in this code.
C-Since x is an instance variable, it cannot be directly used inside a main method. However, it can be accessed through an object such as foo in this code.
D-You cannot create a self-referenced object; that is, foo is created inside the class Foo.
answer
C-
Since x is an instance variable, it cannot be directly used inside a main method. However, it can be accessed through an object such as foo in this code.
question
Analyze the following code:
class Test {
private double i;
public Test(double i) {
this.t( );
this.i = i;
}
public Test( ) {
System.out.println("Default constructor");
this(1);
}
public void t( ) {
System.out.println("Invoking t");
}
}
A- this.t( ) may be replaced by t( ).
B- this.i may be replaced by i.
C- this(1) must be called before
System.out.println("Default constructor").
D- this(1) must be replaced by this(1.0).
answer
A and C
- this.t( ) may be replaced by t( ).
- this(1) must be called before
System.out.println("Default constructor").
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____________ is invoked to create an object.
A constructor
The main method
A method with a return type
A method with the void return type
answer
A constructor
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________ can be accessed from any instance method in the class.
- A local variable
- An instance variable
- A static variable
answer
An instance variable
A static variable
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________ can be accessed from any static method in the class.
- A local variable
- An instane variable
- A static variable
answer
A static variable
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You can use the ______ operator to access members of an object
- .
- ( )
- *
- %
answer
.
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You should add the static keyword in the place of ? in Line ________ in the following code:
public class Test {
private int age;
public ? int square (int n) {
return n * n;
}
public ? int getAge( ) {
return age;
}
}
answer
Both first and second ?'s
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You cannot use the private modifier on classes
True or false?
answer
False
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You can declare two variables with the same name in ________.
-a method one as a formal parameter and the other as a local variable
-a block
-two nested blocks in a method (two nested blocks means one being inside the other)
-different methods in a class
answer
Different methods in a class
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Which of the following statements are true?
-A default constructor is provided automatically if no constructors are explicitly declared in the class.
-At least one constructor must always be defined explicitly.
-Every class has a default constructor.
-The default constructor is a no-arg constructor.
answer
A default constructor is provided automatically if no constructors are explicitly declared in the class.
question
Advantage of encapsulation?
A -Only public methods are needed
B -Making the class final causes no consequential changes to other code.
C -It changes the implementation without changing a class's contract and causes no consequential changes to other code.
D -It changes a class's contract without changing the implementation and causes no consequential changes to other code.
answer
C
It changes the implementation without changing a class's contract and causes no consequential changes to other code.
question
* * *
What is the value of times displayed?
public class Test {
public static void main (String[] args) {
Count myCount = new Count( );
int times = 0;
for (int i=0; i < 100; i++)
increment(myCount, times);
System.out.println(
"myCount.count = " + myCount.count);
System.out.println("times = " + times);
}
public static void increment(Count c, int times) {
c.count++;
times++;
}
}
class Count {
int count;
Count(int c) {
count = c;
}
Count( ) {
count = 1;
}
}
101
100
99
98
0
answer
times = 0
myCount.count = 101
question
* * *
What is the printout of the second println statement in the main method?
public class Foo {
int i;
static int s;
public static void main(String[] args) {
Foo f1 = new Foo( );
System.out.println("f1.i is" + f1.i + "f1.s is" + f1.s);
Foo f2 = new Foo( );
System.out.println("f2.i is" + f2.i + "f2.s is" + f2.s);
Foo f3 = new Foo( );
System.out.println("f3.i is" + f3.i + "f3.s is" + f3.s);
}
public Foo( ) {
i++;
s++;
}
}
A- f2.i is 1 f2.s is 1
B- f2.i is 1 f2.s is 2
C- f2.i is 2 f2.s is 2
D- f2.i is 2 f2.s is 1
answer
B
So because "i" is an instance variable and not a class variable, it will only increment once. But s is a class variable (in fact, you can use s and not f1.s or f2.s or f3.s) and because its a class variable it will increment each time Foo objects are invoked.
question
* * *
Printout for the first statement in the main method?
public class Test {
private int i = 0;
static int j = 0;
public static void main(String[] args) {
new Test( );
}
public Test( ) {
i++;
j++;
int i = 1;
int j = 1;
System.out.println("i is " + j + " j is " + j);
}
}
answer
i is 1 j is 1
So this is because of the int i = 1 and int j = 1 statements which overwrite anyhting else and set i and j both to 1.
If we had made two lines in the main so there would be new Test TWICE, then we would see i only increment once because its a class variable but j would increment twice because its a static variable, or class variable
question
Suppose you declare Date d. d is now called __________.
-an object
-a reference variable for an object
- an object value
- a variable that holds an integer val
answer
a reference variable for an object
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Each class in the file is compiled into a separate bytecode file
True or false?
answer
True
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The pillars of object oriented programming are?
answer
encapsulation, polymorphism, inheritance
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A super class is referred to as a _________ class and sub class is referred to as a __________.
answer
parent; child
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What does polymorphism mean?
answer
Means that a variable of a supertype can refer to a subtype object
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What is object oriented programming?
Or inheritance?
answer
Allows you to define new classes from existing classes, or inheritance
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Who is Ada Lovelace?
answer
English mathematician and write; worked on early mechanical general-purpose computer for Charles Cabbage; her work involved the first algorithm to be carried out by a machine; first computer programmer
