Introduction to Java Final Tips for Taking the Exam

Post by A Debnath on May 5, 2013

Hi Professor Quayle,

The AP Exam is in a couple of days, and though I am feeling very comfortable with the free response section of the exam, I'm still finding the multiple choice questions quite challenging. Are there any multiple choice practice resources that you recommend? Thanks!

Post by Alex Moon on April 28, 2013

I have a few questions....


1.

Does == only check reference?
For example, if
int a = 5
int b = 5
a == b would be false?

2.

Here is what I know.
String[]x;
String[]y=x;


When elements of array y are changed, same change could be observed in array x.

Q: How do you make x and y separate such that a change in x will not reflect change in y?
Would I need to copy each element through iteration? Would I need to declare "new String[10]"?

3.

Under what circumstances could I "upcast"? (cassting to higher class)
ex:

Student s = new Person();
(Person)s ;


4.

I encountered this:


BoxBug bb = new BoxBug();
if ( !bb.canMove())
{ bb.turn();}

why does this result in a compile-time error?

5. When class Student does not have a "no-args" constructor, how come I cannot call "new Student()", when compiler is
supposed to provide a default no-args constructor? In which cases would the default no-args constructor be provided?





6. Consider
Integer intOb = new Integer(3)
Object ob = new Integer(4)

if(intOb.compareTo(ob),0)....

apparently, Barrons says on one of the questions, that this will cause an error.
Strangely, enough, Barrons explained in a chapter that CompareTo automaticall casts the parameter into Integer,
and thus the statement would be legal.

Which is correst? Did Barrons lie to me?


7. If not overriden, does the default equals() method of Object act like == operator? (only comparing the reference)

8. Consider this



Class A
{

public A()
{
methodOne();
}

public void methodOne()
{
print("A");
}
}


Class B extends A
{
public B()
{
print("*")
}

public void methodOne()
{
Print("B");
}
}

Code belod is executed


A object = new B();


Litvin's book says that this happens:

new B() --calls--> A() --calls--> B.methodOne() --print--> "B" --print--> "*",

resulting in
B*


I still don't understand why the A() constructor was called when "new B()" was called!
There was not even a "super()"!



Thank you so much. I hope I'm not bothering you with all these questions. Only a few days until the exam!