This is my mock Exam No 2 based on the Objectives for the Sun Java
Programmers Exam. It was created by Marcus Green (mail@marcusgreen.co.uk) and may be
freely distributed so long as it is unmodified. Please email me if you have any
corrections or comments, but please read this document first
http://www.jchq.net/homepage/getanswers.htm.
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Yes, this is a long document (around 35 pages), if you cannot see the answers then you have not got the entire document, try reloading it untill you can see the answer to Question 60 and the words "End of document". If you cannot load it just keep trying.The answers contain references to approximately which objective the question relates to. If you have a query about any of these questions, please, please include the full answer with the question.
The questions are of a similar format to the real questions, though you get a few "fill in the text box" questions on the real thing. You should assume that the real thing will be harder though many people have told me that they get similar marks in the real thing to my exams.
Check out my FAQ at http://www.jchq.net/faq/jcertfaq.htm for links to other mock exams You can check out my first mock exam that contains 60 question at http://www.jchq.net/mockexams/exam1.htm
What will happen when you attempt to compile and run this code?
abstract class Base{
abstract public void myfunc();
public void another(){
System.out.println("Another method");
}
}
public class Abs extends Base{
public static void main(String argv[]){
Abs a = new Abs();
a.amethod();
}
public void myfunc(){
System.out.println("My func");
}
public void amethod(){
myfunc();
}
}
1) The code will compile and run, printing out the words "My Func"
2) The
compiler will complain that the Base class has non abstract methods
3) The
code will compile but complain at run time that the Base class has non abstract
methods
4) The compiler will complain that the method myfunc in the base
class has no body, nobody at all to looove it
What will happen when you attempt to compile and run this code?
public class MyMain{
public static void main(String argv){
System.out.println("Hello cruel world");
}
}
1) The compiler will complain that main is a reserved word and cannot be used
for a class
2) The code will compile and when run will print out "Hello cruel
world"
3) The code will compile but will complain at run time that no
constructor is defined
4) The code will compile but will complain at run time
that main is not correctly defined
Which of the following are Java modifiers?
1) public
2)
private
3) friendly
4) transient
5) vagrant
What will happen when you attempt to compile and run this code?
class Base{
abstract public void myfunc();
public void another(){
System.out.println("Another method");
}
}
public class Abs extends Base{
public static void main(String argv[]){
Abs a = new Abs();
a.amethod();
}
public void myfunc(){
System.out.println("My func");
}
public void amethod(){
myfunc();
}
}
1) The code will compile and run, printing out the words "My Func"
2) The
compiler will complain that the Base class is not declared as abstract.
3)
The code will compile but complain at run time that the Base class has non
abstract methods
4) The compiler will complain that the method myfunc in the
base class has no body, nobody at all to looove it
Why might you define a method as native?
1) To get to access hardware that Java does not know about
2) To define a
new data type such as an unsigned integer
3) To write optimised code for
performance in a language such as C/C++
4) To overcome the limitation of the
private scope of a method
What will happen when you attempt to compile and run this code?
class Base{
public final void amethod(){
System.out.println("amethod");
}
}
public class Fin extends Base{
public static void main(String argv[]){
Base b = new Base();
b.amethod();
}
}
1) Compile time error indicating that a class with any final methods must be
declared final itself
2) Compile time error indicating that you cannot
inherit from a class with final methods
3) Run time error indicating that
Base is not defined as final
4) Success in compilation and output of
"amethod" at run time.
What will happen when you attempt to compile and run this code?
public class Mod{
public static void main(String argv[]){
}
public static native void amethod();
}
1) Error at compilation: native method cannot be static
2) Error at
compilation native method must return value
3) Compilation but error at run
time unless you have made code containing native amethod available
4)
Compilation and execution without error
What will happen when you attempt to compile and run this code?
private class Base{}
public class Vis{
transient int iVal;
public static void main(String elephant[]){
}
}
1)Compile time error: Base cannot be private
2)Compile time error
indicating that an integer cannot be transient
3)Compile time error transient
not a data type
4)Compile time error malformed main method
What happens when you attempt to compile and run these two files in the same directory?
//File P1.java
package MyPackage;
class P1{
void afancymethod(){
System.out.println("What a fancy method");
}
}
//File P2.java
public class P2 extends P1{
afancymethod();
}
1) Both compile and P2 outputs "What a fancy method" when run
2) Neither
will compile
3) Both compile but P2 has an error at run time
4) P1
compiles cleanly but P2 has an error at compile time
You want to find out the value of the last element of an array. You write the following code. What will happen when you compile and run it.?
public class MyAr{
public static void main(String argv[]){
int[] i = new int[5];
System.out.println(i[5]);
}
}
1) An error at compile time
2) An error at run time
3) The value 0 will
be output
4) The string "null" will be output
You want to loop through an array and stop when you come to the last element.
Being a good java programmer and forgetting everything you ever knew about C/C++
you know that arrays contain information about their size. Which of the
following can you
use?
1)myarray.length();
2)myarray.length;
3)myarray.size
4)myarray.size();
What best describes the appearance of an application with the following code?
import java.awt.*;
public class FlowAp extends Frame{
public static void main(String argv[]){
FlowAp fa=new FlowAp();
fa.setSize(400,300);
fa.setVisible(true);
}
FlowAp(){
add(new Button("One"));
add(new Button("Two"));
add(new Button("Three"));
add(new Button("Four"));
}//End of constructor
}//End of Application
1) A Frame with buttons marked One to Four placed on each edge.
2) A Frame
with buutons marked One to four running from the top to bottom
3) A Frame
with one large button marked Four in the Centre
4) An Error at run time
indicating you have not set a LayoutManager
How do you indicate where a component will be positioned using Flowlayout?
1) North, South,East,West
2) Assign a row/column grid reference
3) Pass
a X/Y percentage parameter to the add method
4) Do nothing, the FlowLayout
will position the component
How do you change the current layout manager for a container
1) Use the setLayout method
2) Once created you cannot change the current
layout manager of a component
3) Use the setLayoutManager method
4) Use
the updateLayout method
Which of the following are fields of the GridBagConstraints class?
1) ipadx
2) fill
3) insets
4) width
What most closely matches the appearance when this code runs?
import java.awt.*;
public class CompLay extends Frame{
public static void main(String argv[]){
CompLay cl = new CompLay();
}
CompLay(){
Panel p = new Panel();
p.setBackground(Color.pink);
p.add(new Button("One"));
p.add(new Button("Two"));
p.add(new Button("Three"));
add("South",p);
setLayout(new FlowLayout());
setSize(300,300);
setVisible(true);
}
}
1) The buttons will run from left to right along the bottom of the
Frame
2) The buttons will run from left to right along the top of the
frame
3) The buttons will not be displayed
4) Only button three will show
occupying all of the frame
Which statements are correct about the anchor field?
1) It is a field of the GridBagLayout manager for controlling component
placement
2) It is a field of the GridBagConstraints class for controlling
component placement
3) A valid setting for the anchor field is
GridBagConstraints.NORTH
4) The anchor field controls the height of
components added to a container
What will happen when you attempt to compile and run the following code?
public class Bground extends Thread{
public static void main(String argv[]){
Bground b = new Bground();
b.run();
}
public void start(){
for (int i = 0; i <10; i++){
System.out.println("Value of i = " + i);
}
}
}
1) A compile time error indicating that no run method is defined for the
Thread class
2) A run time error indicating that no run method is defined for
the Thread class
3) Clean compile and at run time the values 0 to 9 are
printed out
4) Clean compile but no output at runtime
10)When using the GridBagLayout manager, each new component requires a new instance of the GridBagConstraints class. Is this statement
1) true
2) false
Which most closely matches a description of a Java Map?
1) A vector of arrays for a 2D geographic representation
2) A class for
containing unique array elements
3) A class for containing unique vector
elements
4) An interface that ensures that implementing classes cannot
contain duplicate keys
How does the set collection deal with duplicate elements?
1) An exception is thrown if you attempt to add an element with a duplicate
value
2) The add method returns false if you attempt to add an element
with a duplicate value
3) A set may contain elements that return duplicate
values from a call to the equals method
4) Duplicate values will cause an
error at compile time
What can cause a thread to stop executing?
1) The program exits via a call to System.exit(0);
2) Another thread is
given a higher priority
3) A call to the thread's stop method.
4) A call
to the halt method of the Thread class
For a class defined inside a method, what rule governs access to the variables of the enclosing method?
1) The class can access any variable
2) The class can only access static
variables
3) The class can only access transient variables
4) The class
can only access final variables
Under what circumstances might you use the yield method of the Thread
class
1) To call from the currently running thread to allow another thread of the
same or higher priority to run
2) To call on a waiting thread to allow it to
run
3) To allow a thread of higher priority to run
4) To call from the
currently running thread with a parameter designating which thread should be
allowed to run
What will happen when you attempt to compile and run the following code
public class Hope{
public static void main(String argv[]){
Hope h = new Hope();
}
protected Hope(){
for(int i =0; i <10; i ++){
System.out.println(i);
}
}
}
1) Compilation error: Constructors cannot be declared protected
2) Run
time error: Constructors cannot be declared protected
3) Compilation and
running with output 0 to 10
4) Compilation and running with output 0 to 9
What will happen when you attempt to compile and run the following code
public class MySwitch{
public static void main(String argv[]){
MySwitch ms= new MySwitch();
ms.amethod();
}
public void amethod(){
int k=10;
switch(k){
default: //Put the default at the bottom, not here
System.out.println("This is the default output");
break;
case 10:
System.out.println("ten");
case 20:
System.out.println("twenty");
break;
}
}
}
1) None of these options
2) Compile time error target of switch must be an
integral type
3) Compile and run with output "This is the default
output"
4) Compile and run with output of the single line "ten"
Which of the following is the correct syntax for suggesting that the JVM performs garbage collection
1) System.free();
2) System.setGarbageCollection();
3)
System.out.gc();
4) System.gc();
What will happen when you attempt to compile and run the following
code
public class As{
int i = 10;
int j;
char z= 1;
boolean b;
public static void main(String argv[]){
As a = new As();
a.amethod();
}
public void amethod(){
System.out.println(j);
System.out.println(b);
}
}
1) Compilation succeeds and at run time an output of 0 and false
2)
Compilation succeeds and at run time an output of 0 and true
3) Compile time
error b is not initialised
4) Compile time error z must be assigned a char
value
What will happen when you attempt to compile and run the following code
with the command line "hello there"
public class Arg{
String[] MyArg;
public static void main(String argv[]){
MyArg=argv;
}
public void amethod(){
System.out.println(argv[1]);
}
}
1) Compile time error
2) Compilation and output of "hello"
3)
Compilation and output of "there"
4) None of the above
What will happen when you attempt to compile and run the following code
public class StrEq{
public static void main(String argv[]){
StrEq s = new StrEq();
}
private StrEq(){
String s = "Marcus";
String s2 = new String("Marcus");
if(s == s2){
System.out.println("we have a match");
}else{
System.out.println("Not equal");
}
}
}
1) Compile time error caused by private constructor
2) Output of "we have
a match"
3) Output of "Not equal"
4) Compile time error by attempting to
compare strings using ==
1) What will happen when you attempt to compile and run the following code
import java.io.*;
class Base{
public static void amethod()throws FileNotFoundException{}
}
public class ExcepDemo extends Base{
public static void main(String argv[]){
ExcepDemo e = new ExcepDemo();
}
public static void amethod(){}
protected ExcepDemo(){
try{
DataInputStream din = new DataInputStream(System.in);
System.out.println("Pausing");
din.readChar();
System.out.println("Continuing");
this.amethod();
}catch(IOException ioe) {}
}
}
1)Compile time error caused by protected constructor
2) Compile time error
caused by amethod not declaring Exception
3) Runtime error caused by
amethod not declaring Exception
4) Compile and run with output of "Pausing"
and "Continuing" after a key is hit
Answer to Question
31)
What will happen when you attempt to compile and run this program
public class Outer{
public String name = "Outer";
public static void main(String argv[]){
Inner i = new Inner();
i.showName();
}//End of main
private class Inner{
String name =new String("Inner");
void showName(){
System.out.println(name);
}
}//End of Inner class
}
1) Compile and run with output of "Outer"
2) Compile and run with output
of "Inner"
3) Compile time error because Inner is declared as private
4)
Compile time error because of the line creating the instance of Inner
What will happen when you attempt to compile and run this code
//Demonstration of event handling
import java.awt.event.*;
import java.awt.*;
public class MyWc extends Frame implements WindowListener{
public static void main(String argv[]){
MyWc mwc = new MyWc();
}
public void windowClosing(WindowEvent we){
System.exit(0);
}//End of windowClosing
public void MyWc(){
setSize(300,300);
setVisible(true);
}
}//End of class
1) Error at compile time
2) Visible Frame created that that can be
closed
3) Compilation but no output at run time
4) Error at compile time
because of comment before import statements
Which option most fully describes will happen when you attempt to compile and run the following code
public class MyAr{
public static void main(String argv[]) {
MyAr m = new MyAr();
m.amethod();
}
public void amethod(){
static int i;
System.out.println(i);
}
}
1) Compilation and output of the value 0
2) Compile time error because i
has not been initialized
3) Compilation and output of null
4) Compile time
error
Which of the following will compile correctly
1) short myshort = 99S;
2) String name = 'Excellent tutorial Mr
Green';
3) char c = 17c;
4)int z = 015;
Which of the following are Java key
words
1)double
2)Switch
3)then
4)instanceof
What
will be output by the following line?
System.out.println(Math.floor(-2.1));
1) -2
2) 2.0
3) -3
4) -3.0
Given the following main method in a class called Cycle and a command line of
java Cycle one two
what will be output?
public static void main(String bicycle[]){
System.out.println(bicycle[0]);
}
1) None of these options
2) cycle
3) one
4) two
Which of the following statements are true?
1) At the root of the collection hierarchy is a class called Collection
2)
The collection interface contains a method called enumerator
3) The interator
method returns an instance of the Vector class
4) The set interface is
designed for unique elements
Which of the following statements are correct?
1) If multiple listeners are added to a component only events for the last
listener added will be processed
2) If multiple listeners are added to a
component the events will be processed for all but with no guarantee in the
order
3) Adding multiple listeners to a comnponent will cause a compile time
error
4) You may remove as well add listeners to a component.
Given the following code
class Base{}
public class MyCast extends Base{
static boolean b1=false;
static int i = -1;
static double d = 10.1;
public static void main(String argv[]){
MyCast m = new MyCast();
Base b = new Base();
//Here
}
}
Which of the following, if inserted at the comment //Here will allow the code
to compile and run without error
1) b=m;
2) m=b;
3) d =i;
4) b1
=i;
Which of the following statements about threading are true
1) You can only obtain a mutually exclusive lock on methods in a class that
extends Thread or implements runnable
2) You can obtain a mutually exclusive
lock on any object
3) A thread can obtain a mutually exclusive lock on a
method declared with the keyword synchronized
4) Thread scheduling algorithms
are platform dependent
Your chief Software designer has shown you a sketch of the new Computer parts system she is about to create. At the top of the hierarchy is a Class called Computer and under this are two child classes. One is called LinuxPC and one is called WindowsPC.
The main difference between the two is that one runs the Linux operating System and the other runs the Windows System (of course another difference is that one needs constant re-booting and the other runs reliably). Under the WindowsPC are two Sub classes one called Server and one Called Workstation. How might you appraise your designers work?
1) Give the goahead for further design using the current scheme
2) Ask
for a re-design of the hierarchy with changing the Operating System to a field
rather than Class type
3) Ask for the option of WindowsPC to be removed as it
will soon be obsolete
4) Change the hierarchy to remove the need for the
superfluous Computer Class.
Which of the following statements are true
1) An inner class may be defined as static
2) There are NO circumstances
where an inner class may be defined as private
3) An anonymous class may have
only one constructor
4) An inner class may extend another class
What will happen when you attempt to compile and run the following code
int Output=10;
boolean b1 = false;
if((b1==true) && ((Output+=10)==20)){
System.out.println("We are equal "+Output);
}else
{
System.out.println("Not equal! "+Output);
}
1) Compile error, attempting to peform binary comparison on logical data
type
2) Compilation and output of "We are equal 10"
3) Compilation and
output of "Not equal! 20"
4) Compilation and output of "Not equal! 10"
Given the following variables which of the following lines will compile without error?
String s = "Hello"; long l = 99; double d = 1.11; int i = 1; int j = 0;
1) j= i <<s; 2) j= i<<j; 3) j=i<<d; 4)j=i<<l;
What will be output by the following line of code?
System.out.println(010|4);
1) 14
2) 0
3) 6
4) 12
Given the following variables
char c = 'c'; int i = 10; double d = 10; long l = 1; String s = "Hello";
Which of the following will compile without error?
1)c=c+i;
2)s+=i;
3)i+=s;
4)c+=s;
Which of the following will compile without error?
1) File f = new File("/","autoexec.bat");
2) DataInputStream d = new
DataInputStream(System.in);
3) OutputStreamWriter o = new
OutputStreamWriter(System.out);
4) RandomAccessFile r = new
RandomAccessFile("OutFile");
Given the folowing classes which of the following will compile without error?
interface IFace{}
class CFace implements IFace{}
class Base{}
public class ObRef extends Base{
public static void main(String argv[]){
ObRef ob = new ObRef();
Base b = new Base();
Object o1 = new Object();
IFace o2 = new CFace();
}
}
1)o1=o2; 2)b=ob; 3)ob=b; 4)o1=b;
Given the following code what will be the output?
class ValHold{
public int i = 10;
}
public class ObParm{
public static void main(String argv[]){
ObParm o = new ObParm();
o.amethod();
}
public void amethod(){
int i = 99;
ValHold v = new ValHold();
v.i=30;
another(v,i);
System.out.println(v.i);
}//End of amethod
public void another(ValHold v, int i){
i=0;
v.i = 20;
ValHold vh = new ValHold();
v = vh;
System.out.println(v.i+ " "+i);
}//End of another
}
1) 10,0, 30
2) 20,0,30
3) 20,99,30
4) 10,0,20
Given the following class definition, which of the following methods could be legally placed after the comment
//Here
public class Rid{
public void amethod(int i, String s){}
//Here
}
1)public void amethod(String s, int i){}
2)public int amethod(int i,
String s){}
3)public void amethod(int i, String mystring){}
4) public
void Amethod(int i, String s) {}
Given the following class definition which of the following can be legally
placed after the comment line
//Here ?
class Base{
public Base(int i){}
}
public class MyOver extends Base{
public static void main(String arg[]){
MyOver m = new MyOver(10);
}
MyOver(int i){
super(i);
}
MyOver(String s, int i){
this(i);
//Here
}
}
1)MyOver m = new MyOver();
2)super();
3)this("Hello",10);
4)Base b
= new Base(10);
Given the following class definition, which of the following statements would be legal after the comment //Here
class InOut{
String s= new String("Between");
public void amethod(final int iArgs){
int iam;
class Bicycle{
public void sayHello(){
//Here
}//End of bicycle class
}
}//End of amethod
public void another(){
int iOther;
}
}
1)System.out.println(s);
2) System.out.println(iOther);
3)
System.out.println(iam);
4) System.out.println(iArgs);
Which of the following are methods of the Thread class?
1) yield()
2) sleep(long msec)
3) go()
4) stop()
Which of the following methods are members of the Vector class and allow you to input a new element
1) addElement
2) insert
3) append
4) addItem
Which of the following statements are true?
1) Adding more classes via import statements will cause a performance
overhead, only import classes you actually use.
2) Under no circumstances can
a class be defined with the private modifier
3) A inner class may
under some circumstances be defined with the protected modifier
4) An
interface cannot be instantiated
Which of the following are correct event handling methods
1) mousePressed(MouseEvent e){}
2) MousePressed(MouseClick e){}
3)
functionKey(KeyPress k){}
4) componentAdded(ContainerEvent e){}
Which of the following are methods of the Collection interface?
1)
iterator
2) isEmpty
3) toArray
4) setText
Which of the following best describes the use of the synhronized keyword?
1) Allows two process to run in paralell but to communicate with each
other
2) Ensures only one thread at a time may access a method or
object
3) Ensures that two or more processes will start and end at the same
time
4) Ensures that two or more Threads will start and end at the same
time
Objective 1.2)
1) The code will compile and run, printing out the words "My Func"
A class that contains an abstract method must be declared abstract itself, but may contain non abstract methods.
Objective 4.1)
4) The code will compile but will complain at run time that main is not correctly defined
In this example the parameter is a string not a string array as needed for the correct main method
Objective 4.3)
1) public
2) private
4) transient
The keyword transient is easy to forget as is not frequently used. Although a method may be considered to be friendly like in C++ it is not a Java keyword.
Objective 1.2)
2) The compiler will complain that the Base class is not declared as abstract.
If a class contains abstract methods it must itself be declared as abstract
Objective 1.2)
1) To get to access hardware that Java does not know about
3) To write
optimised code for performance in a language such as C/C++
Objective 1.2)
4) Success in compilation and output of "amethod" at run time.
A final method cannot be ovverriden in a sub class, but apart from that it does not cause any other restrictions.
Objective 1.2)
4) Compilation and execution without error
It would cause a run time error if you had a call to amethod though.
Objective 1.2)
1)Compile time error: Base cannot be private
A top leve (non nested) class cannot be private.
Objective 1.2)
4) P1 compiles cleanly but P2 has an error at compile time
The package statement in P1.java is the equivalent of placing the file in a different directory to the file P2.java and thus when the compiler tries to compile P2 an error occurs indicating that superclass P1 cannot be found.
Objective 1.1)
2) An error at run time
This code will compile, but at run-time you will get an ArrayIndexOutOfBounds exception. This becuase counting in Java starts from 0 and so the 5th element of this array would be i[4].
Remember that arrays will always be initialized to default values wherever they are created.
Objective 1.1)
2)myarray.length;
The String class has a length() method to return the number of characters. I have sometimes become confused between the two.
Objective 8.2)
3) A Frame with one large button marked Four in the Centre
The default layout manager for a Frame is the BorderLayout manager. This Layout manager defaults to placing components in the centre if no constraint is passed with the call to the add method.
Objective 8.2)
4) Do nothing, the FlowLayout will position the component
Objective 8.2)
1) Use the setLayout method
Objective 8.2)
1) ipadx
2) fill
3) insets
Objective 8.2)
2) The buttons will run from left to right along the top of the
frame
The call to the setLayout(new FlowLayout()) resets the Layout
manager for the entire frame and so the buttons end up at the top rather than
the bottom.
Objective 8.2)
2) It is a field of the GridBagConstraints class for controlling component
placement
3) A valid settting for the anchor field is
GridBagconstraints.NORTH
Objective 7.1)
4) Clean compile but no output at runtime
This is a bit of a sneaky one as I have swapped around the names of the
methods you need to define and call when running a thread. If the for loop were
defined in a method called
public void run()
and the call in the main method had been to b.start()
The list of values from 0 to 9 would have been output.
Objective 8.2)
2) false
You can re-use the same instance of the GridBagConstraints
when added successive components.
Objective 10.1)
4) An interface that ensures that implementing classes cannot contain duplicates
Objective 10.1)
2) The add method returns false if you attempt to add an element with a duplicate value
I find it a surprise that you do not get an exception.
Objective 7.1)
1) The program exits via a call to exit(0);
2) The priority of another
thread is increased
3) A call to the stop method of the Thread class
Java threads are somewhat platform dependent and you should be carefull
when making assumptions about Thread priorities. On some platforms you may find
that a Thread with higher priorities gets to "hog" the processor. You can read
up on this in more detail at http://java.sun.com/docs/books/tutorial/essential/threads/priority.html
Objective 4.1)
4) The class can only access final variables
Objective 7.1)
1) To call from the currently running thread to allow another thread of
the same or higher priority to run
Option 3 looks plausible but there is no guarantee that the thread that grabs the cpu time will be of a higher priority. It will depend on the threading algorithm of the Java Virtual Machine and the underlying operating system
Objective 6.2)
4) Compilation and running with output 0 to 9
Objective 2.1)
1) None of these options
Because of the lack of a break statement
after the break 10; statement the actual output will be
"ten" followed
by "twenty"
Objective 3.1)
4) System.gc();
Objective 4.4)
1) Compilation succeeds and at run time an output of 0 and false
The
default value for a boolean declared at class level is false, and integer is
0;
Objective 1.2)
1) Compile time error
You will get an error saying something like "Cant make a static reference to a non static variable". Note that the main method is static.
Objective 5.2)
3) Output of "Not equal"
Despite the actual character strings matching, using the == operator will simply compare memory location. Because the one string was created with the new operator it will be in a different location in memory to the other string.
Objective 2.3)
4) Compile and run with output of "Pausing" and "Continuing" after a key is hit
An overriden method in a sub class must not throw Exceptions not thrown in the base class. In the case of the method amethod it throws no exceptions and will thus compile without complain. There is no reason that a constructor cannot be protected.
Objective 6.3)
4) Compile time error because of the line creating the instance of Inner
This looks like a question about inner classes but it is also a reference
to the fact that the main method is static and thus you cannot directly access a
non static method. The line causing the error could be fixed by changing it to
say
Inner i = new Outer().new Inner();
Then the code would compile and run producing the output "Inner"
Objective 4.6)
1) Error at compile time
If you implement an interface you must create bodies for all methods in that interface. This code will produce an error saying that MyWc must be declared abstract because it does not define all of the methods in WindowListener. Option 4 is nonsense as comments can appear anywhere. Option 3 suggesting that it might compile but not produce output is ment to mislead on the basis that what looks like a constructor is actually an ordinary method as it has a return type.
Objective 1.2)
4) Compile time error
An error will be caused by attempting to define an integer as static within a method. The lifetime of a field within a method is the duration of the running of the method. A static field exists once only for the class. An approach like this does work with Visual Basic.
Objective 9.5)
4)int z = 015;
The letters c and s do not exist as literal indicators and a String must be enclosed with double quotes, not single as in this case.
Objective 4.3)
1)double
4)instanceof
Note the upper case S on switch means it is
not a keyword and the word then is part of Visual Basic but not Java. Also,
instanceof looks like a method but is actually a keyword,
Objective 9.2)
4) -3.0
Objective 4.2)
3) one
Command line parameters start from 0 and fromt he first parameter after the name of the compile (normally Java)
Objective 10.1)
4) The set is designed for unique elements.
Collection is an interface, not a class. The Collection interface includes a
method called iterator. This returns an instance of the Iterator class which has
some similarities with Enumerators.
The name set should give away the purpose
of the Set interface as it is analogous to the Set concept in relational
databases which implies uniquness.
Objective 8.1)
2) If multiple listeners are added to a component the events will be
processed for all but with no guarantee in the order
4) You may remove as
well add listeners to a component.
It ought to be fairly intuitive that a component ought to be able to have
multiple listeners. After all, a text field might want to respond
to both the mouse and keyboard
Objective 5.1)
1) b=m;
3) d =i;
You can assign up the inheritance tree from a child to a parent but not the other way without an explicit casting. A boolean can only ever be assigned a boolean value.
Objective 7.3)
2) You can obtain a mutually exclusive lock on any object
3) A thread can
obtain a mutually exclusive lock on a method declared with the keyword
synchronized
4) Thread scheduling algorithms are platform dependent
Yes that says dependent and not independent.
Objective 6.1)
2) Ask for a re-design of the hierarchy with changing the Operating System to a field rather than Class type
This question is about the requirement to understand the difference between the "is-a" and the "has-a" relationship. Where a class is inherited you have to ask if it represents the "is-a" relationship. As the difference between the root and the two children are the operating system you need to ask are Linux and Windows types of computers.The answer is no, they are both types of Operating Systems. So option two represents the best of the options. You might consider having operating system as an interface instead but that is another story.
Of course there are as many ways to design an object hierarchy as ways to pronounce Bjarne Strousjoup, but this is the sort of answer that Sun will proabably be looking for in the exam. Questions have been asked in discussion forums if this type of question really comes up in the exam. I think this is because some other mock exams do not contain any questions like this. I assure you that this type of question can come up in the exam. These types of question are testing your understanding of the difference between the is-a and has-a relationship in class design.
Objective 4.1)
1) An inner class may be defined as static
4) An inner class may extend
another class
A static inner class is also sometimes known as a top level nested class. There is some debate if such a class should be called an inner class. I tend to think it should be on the basis that it is created inside the opening braces of another class. How could an anonymous class have a constructor?. Remember a constructor is a method with no return type and the same name as the class. Inner classes may be defined as private
Objective 5.3)
4) Compilation and output of "Not equal! 10"
The output will be "Not equal 10". This illustrates that the Output +=10 calculation was never performed because processing stopped after the first operand was evaluated to be false. If you change the value of b1 to true processing occurs as you would expect and the output is "We are equal 20";.
Objective 5.1)
2)j= i<<j; 4)j=i<<l;
Objective 5.3)
4) 12
As well as the binary OR objective this questions requires you to understand the octal notaction which means that the leading letter zero (not the letter O)) means that the first 1 indicates the number contains one eight and nothing else. Thus this calculation in decimal mean
8|4
To convert this to binary means
1000 0100 •• 1100 ••
Which is 12 in decimal
The | bitwise operator means that for each position where there is a 1, results in a 1 in the same position in the answer.
Objective 5.1)
2)s+=i;
Only a String acts as if the + operator were overloaded
Objective 10.1)
Although the objectives do not specifically mention the need to understand the I/O Classes, feedback from people who have taken the exam indicate that you will get questions on this topic. As you will probably need to know this in the real world of Java programming, get familiar with the basics. I have assigned these questions to Objective 10.1 as that is a fairly vague objective.
1) File f = new File("/","autoexec.bat");
2) DataInputStream d = new
DataInputStream(System.in);
3) OutputStreamWriter o = new
OutputStreamWriter(System.out);
Option 4, with the RandomAccess file will not compile because the constructor must also be passed a mode parameter which must be either "r" or "rw"
Objective 5.1)
1)o1=o2; 2)b=ob; 4)o1=b;
Objective 5.4)
4) 10,0,20
In the call
another(v,i);
A reference to v is passed and thus any changes will be intact after this call.
Objective 6.2)
1) public void amethod(String s, int i){}
4) public void
Amethod(int i, String s) {}
Overloaded methods are differentiated only on the number, type and order of parameters, not on the return type of the method or the names of the parameters.
Objective 6.2)
4)Base b = new Base(10);
Any call to this or super must be the first line in a constructor. As the method already has a call to this, no more can be inserted.
Objective 4.1)
1)System.out.println(s);
4) System.out.println(iArgs);
A class within a method can only see final variables of the enclosing method. However it the normal visibility rules apply for variables outside the enclosing method.
Objective 7.2)
1) yield()
2) sleep
4) stop()
Note, the methods stop and suspend have been deprecated with the Java2
release, and you may get questions on the exam that expect you to know this.
Check out the Java2 Docs for an explanation
Objective 10.1)
1) addElement
Objective 4.1)
The import statement allows you to use a class directly instead of fully qualifying it with the full package name, adding more classess with the import statement does not cause a runtime performance overhad. I assure you this is true. An inner class can be defined with the private modifier.
3) An inner class can be defined with the protected modifier
4) An
interface cannot be instantiated
Objective 4.6)
1) mousePressed(MouseEvent e){}
4) componentAdded(ContainerEvent e){}
Objective 10.1)
1) iterator
2) isEmpty
3) toArray
Objective 7.3)
2) 2) Ensures only one thread at a time may access a method or object
End of document
Marcus Green copyright 2000