This is a mock Exam based on the Objectives for the Sun Java Programmers
Exam.
Because the Objectives for the Java2 exam are very similar to the Objectives for the 1.1 exam, this test is appropriate for studying for the new exam. Questions from 45 onward may include objectives from Java2 exam.
If you have your own ideas for questions, send them to me with answers and explanations. If they look good I'll post them and include a credit with your name and email address (if you like). Each question may have one or more correct answers.
Which of the following lines will compile without warning or error.
1) float f=1.3;
2) char c="a";
3) byte b=257;
4) boolean b=null;
5) int i=10;
What will happen if you try to compile and run the following code
public class MyClass {
public static void main(String arguments[]) {
amethod(arguments);
}
public void amethod(String[] arguments) {
System.out.println(arguments);
System.out.println(arguments[1]);
}
}
1) error Can't make static reference to void amethod.
2) error method
main not correct
3) error array must include parameter
4) amethod must
be declared with String
Which of the following will compile without error
1)
import java.awt.*;
package Mypackage;
class Myclass {}
2)
package MyPackage;
import java.awt.*;
class MyClass{}
3)
/*This is a comment */
package MyPackage;
import java.awt.*;
class MyClass{}
A byte can be of what size
1) -128 to 127
2) (-2 power 8 )-1 to 2 power 8
3) -255 to 256
4)depends on the particular implementation of the Java Virtual machine
What will be printed out if this code is run with the following command line?
java myprog good morning
public class myprog{
public static void main(String argv[])
{
System.out.println(argv[2])
}}
1) myprog
2) good
3) morning
4) Exception raised:
"java.lang.ArrayIndexOutOfBoundsException: 2"
Which of the following are java reserved
words?
1) if
2) then
3) goto
4) while
5) case
Which of the following are legal identifiers
1) 2variable
2) variable2
3) _whatavariable
4) _3_
5)
$anothervar
6) #myvar
What will happen when you compile and run the following
code?
public class MyClass{
static int i;
public static void main(String argv[]){
System.out.println(i);
}
}
1) Error Variable i may not have been initialized
2) null
3) 1
4)
0
What will happen if you try to compile and run the following code?
public class Q {
public static void main(String argv[]){
int anar[]=new int[]{1,2,3};
System.out.println(anar[1]);
}
}
1) 1
2) Error anar is referenced before it is initialized
3) 2
4)
Error: size of array must be defined
What will happen if you try to compile and run the
following code?
public class Q {
public static void main(String argv[]){
int anar[]=new int[5];
System.out.println(anar[0]);
}
}
1) Error: anar is referenced before it is initialized
2) null
3) 0
4) 5
What will be the result of attempting to compile and run
the following code?
abstract class MineBase {
abstract void amethod();
static int i;
}public class Mine extends MineBase {
public static void main(String argv[]){
int[] ar=new int[5];
for(i=0;i < ar.length;i++)
System.out.println(ar[i]);
}
}
1) a sequence of 5 0's will be printed
2) Error: ar is used before it is
initialized
3) Error Mine must be declared abstract
4) IndexOutOfBoundes
Error
What will be printed out if you attempt to compile and run the following code ?
int i=1;
switch (i) {
case 0:
System.out.println("zero");
break;
case 1:
System.out.println("one");
case 2:
System.out.println("two");
default:
System.out.println("default");
}
1) one
2) one, default
3) one, two, default
4) default
What will be printed out if you attempt to compile and run the following code?
int i=9;
switch (i) {
default:
System.out.println("default");
case 0:
System.out.println("zero");
break;
case 1:
System.out.println("one");
case 2:
System.out.println("two");
}
1) default
2) default, zero
3) error default clause not defined
4) no output displayed
Which of the following lines of code will compile without error
1)
int i=0;
if(i) {
System.out.println("Hello");
}
2)
boolean b=true;
boolean b2=true;
if(b==b2) {
System.out.println("So true");
}
3)
int i=1;
int j=2;
if(i==1|| j==2)
System.out.println("OK");
4)
int i=1;
int j=2;
if(i==1 &| j==2)
System.out.println("OK");
What will be output if you try to compile and run the
following code, but there is
no file called Hello.txt in the current
directory?.
import java.io.*;
public class Mine {
public static void main(String argv[]){Mine m=new Mine(); System.out.println(m.amethod()); }
public int amethod() {
try {
FileInputStream dis=new FileInputStream("Hello.txt");
}catch (FileNotFoundException fne) {
System.out.println("No such file found");
return -1;
}catch(IOException ioe) {
} finally{
System.out.println("Doing finally");
}
return 0;
}
}
1) No such file found
2 No such file found ,-1
3) No such file found,
Doing finally, -1
4) 0
What tags are mandatory when creating HTML to display an applet
1) name, height, width
2) code, name
3) codebase, height, width
4) code, height, width
What will happen if you attempt to compile and run the following code?
1) Compile and run without error
2) Compile time Exception
3) Runtime
Exception
class Base {}
class Sub extends Base {}
class Sub2 extends Base {}public class CEx{ public static void main(String argv[]){
Base b=new Base();
Sub s=(Sub) b;
}}
If the following HTML code is used to display the applet in
the code MgAp what will
be displayed at the console?
1) Error: no such parameter
2) 0
3) null
4) 30
<applet name=MgAp code=MgAp.class height=400 width=400 parameter HowOld=30
>
</applet>
import java.applet.*;
import java.awt.*;
public class MgAp extends Applet{
public void init(){
System.out.println(getParameter("age"));
}
}
You are browsing the Java HTML documentation for information
on the
java.awt.TextField component. You want to create Listener code to
respond to focus
events. The only Listener method listed is
addActionListener. How do you go about
finding out about Listener
methods?
1) Define your own Listener interface according to the event to be tracked
2) Use the search facility in the HTML documentation for the listener needed
3) Move up the hierarchy in the HTML documentation to locate methods in base
classes
4) Subclass awt.event with the appropriate Listener method
What will be displayed when you attempt to compile and
run the following code
//Code start import java.awt.*;
public class Butt extends Frame{public static void main(String argv[]){
Butt MyBut=new Butt();
}Butt(){
Button HelloBut=new Button("Hello");
Button ByeBut=new Button("Bye");
add(HelloBut);
add(ByeBut);
setSize(300,300);
setVisible(true);
}
}
//Code end
1) Two buttons side by side occupying all of the frame, Hello on the left and
Bye on
the right
2) One button occupying the entire frame saying Hello
3) One button occupying the entire frame saying Bye
4) Two buttons at
the top of the frame one saying Hello the other saying Bye
What will be output by the following code?
public class MyFor{
public static void main(String argv[]){
int i;
int j;
outer:
for (i=1;i <3;i++)
inner:
for(j=1; j<3; j++) {
if (j==2)
continue outer;
System.out.println("Value for i=" + i + " Value for j=" +j);
}
}
}
1) Value for i=1 value for j=1
2) value for i=2 value for j=1
3)
value for i=2 value for j=2
4 value for i=3 value for j=1
If g is a graphics instance what will the following code
draw on the screen?.
g.fillArc(45,90,50,50,90,180);
1) An arc bounded by a box of height 45, width 90 with a centre point of
50,50, starting
at an angle of 90 degrees traversing through 180 degrees
counter clockwise.
2) An arc bounded by a box of height 50, width 50, with a centre point of
45,90 starting
at an angle of 90 degrees traversing through 180 degrees
clockwise.
3) An arc bounded by a box of height 50, width 50, with a top left at
coordinates of 45,
90, starting at 90 degrees and traversing through 180
degrees counter clockwise.
4) An arc starting at 45 degrees, traversing through 90 degrees clockwise
bounded by a
box of height 50, width 50 with a centre point of 90, 180.
Which of the following methods can be legally inserted in
place of the comment //Method Here ?
class Base{
public void amethod(int i) { }
}
public class Scope extends Base{
public static void main(String argv[]){
}
//Method Here
}
1) void amethod(int i) throws Exception {}
2) void amethod(long i)throws
Exception {}
3) void amethod(long i){}
4) public void amethod(int i)
throws Exception {}
Which of the following will output -4.0
1) System.out.println(Math.floor(-4.7));
2)
System.out.println(Math.round(-4.7));
3)
System.out.println(Math.ceil(-4.7));
4)
System.out.println(Math.Min(-4.7));
What will happen if you attempt to compile and run the
following code?
Integer ten=new Integer(10); Long nine=new Long (9);
System.out.println(ten + nine); int i=1;
System.out.println(i + ten);
1) 19 followed by 20
2) 19 followed by 11
3) Error: Can't convert
java lang Integer
4) 10 followed by 1
If you run the code below, what gets printed
out?
String s=new String("Bicycle");
int iBegin=1;
char iEnd=3;
System.out.println(s.substring(iBegin,iEnd));
1) Bic
2) ic
3) icy
4) error: no method matching
substring(int,char)
If you wanted to find out where the position of the letter v
(ie return 2) in the string s
containing "Java", which of the following
could you use?
1) mid(2,s);
2) charAt(2);
3) s.indexOf('v');
4)
indexOf(s,'v');
Given the following declarations
String s1=new String("Hello")
String s2=new String("there");
String s3=new String();
Which of the following are legal operations?
1) s3=s1 + s2;
2) s3=s1-s2;
3) s3=s1 & s2
4) s3=s1 &&
s2
What is the result of the following operation?
System.out.println(4 | 3);
1) 6
2) 0
3) 1
4) 7
public class MyClass1 {public static void main(String argv[]){ }
/*Modifier at XX */ class MyInner {}}
What modifiers would be legal at XX in the above code?
1) public
2) private
3) static
4) friend
How would you go about opening an image file called
MyPicture.jpg
1) Graphics.getGraphics("MyPicture.jpg");
2) Image
image=Toolkit.getDefaultToolkit().getImage("MyPicture.jpg");
3)
Graphics.openImage("MyPicture");
4) Image m=new Image("MyPicture");
An Applet has its Layout Manager set to the default of FlowLayout. What code would be correct to change to another Layout Manager.
1) setLayoutManager(new GridLayout());
2) setLayout(new GridLayout(2,2));
3) setGridLayout(2,2,))
4) setBorderLayout();
What will happen when you attempt to compile and run the
following code?.
1) It will compile and the run method will print out the increasing value of
i.
2) It will compile and calling start will print out the increasing value
of i.
3) The code will cause an error at compile time.
4) Compilation
will cause an error because while cannot take a parameter of true.
class Background implements Runnable{
int i=0;
public int run(){
while(true){
i++;
System.out.println("i="+i);
} //End while
}//End run
}//End class
You have created an applet that draws lines. You have overriden the paint operation and used the graphics drawLine method, and increase one of its parameters to multiple lines across the screen. When you first test the applet you find that the news lines are redrawn, but the old lines are erased. How can you modify your code to allow the old lines to stay on the screen instead of being cleared.
1) Override repaint thus
public void repaint(Graphics g){
paint(g);
}
2)Override update thus
public void update(Graphics g) {
paint(g);
}
3) turn off clearing with the method setClear();
4) Remove the drawing from the paint Method and place in the calling code
What will be the result when you attempt to compile and
run the following code?.
public class Conv{
public static void main(String argv[]){
Conv c=new Conv();
String s=new String("ello");
c.amethod(s);
}
public void amethod(String s){
char c='H';
c+=s;
System.out.println(c);
}
}
1) Compilation and output the string "Hello"
2) Compilation and output
the string "ello"
3) Compilation and output the string elloH
4) Compile
time error
Given the following code, what test would you need to put in place of the comment line?
//place test here
to result in an output of
Equal
public class EqTest{
public static void main(String argv[]){
EqTest e=new EqTest();
}
EqTest(){
String s="Java";
String s2="java";
//place test here {
System.out.println("Equal");
}else
{
System.out.println("Not equal");
}
}
}
1) if(s==s2)
2) if(s.equals(s2)
3) if(s.equalsIgnoreCase(s2))
4)if(s.noCaseMatch(s2))
Given the following code
import java.awt.*;
public class SetF extends Frame{
public static void main(String argv[]){
SetF s=new SetF();
s.setSize(300,200);
s.setVisible(true);
}
}
How could you set the frame surface color to pink
1)s.setBackground(Color.pink);
2)s.setColor(PINK);
3)s.Background(pink);
4)s.color=Color.pink
How can you change the current working directory using an
instance of the File class called FileName?
1)
FileName.chdir("DirName")
2) FileName.cd("DirName")
3)
FileName.cwd("DirName")
4) The File class does not support directly changing
the current directory.
If you create a TextField with a constructor to set it to occupy 5 columns, what difference will it make if you use it with a proportional font (ie Times Roman) or a fixed pitch typewriter style font (Courier).
1)With a fixed font you will see 5 characters, with a proportional it
will depend on the width of the characters
2)With a fixed font you will see
5 characters,with a proportional it will cause the field to expand to fit
the text
3)The columns setting does not affect the number of characters
displayed
4)Both will show exactly 5 characters
Given the following code how could you invoke the Base
constructor that will print out the string "base constructor";
class Base{
Base(int i){
System.out.println("base constructor");
}
Base(){
}
}
public class Sup extends Base{
public static void main(String argv[]){
Sup s= new Sup();
//One
}
Sup()
{
//Two
}
public void derived()
{
//Three
}
}
1) On the line After //One put Base(10);
2) On the line After //One put
super(10);
3) On the line After //Two put super(10);
4) On the line After
//Three put super(10);
Given the following code what will be output?
public class Pass{
static int j=20;
public static void main(String argv[]){
int i=10;
Pass p = new Pass();
p.amethod(i);
System.out.println(i);
System.out.println(j);
}
public void amethod(int x){
x=x*2;
j=j*2;
}
}
1) Error: amethod parameter does not match variable
2) 20 and 40
3) 10
and 40
4) 10, and 20
What code placed after the comment //For loop would
populate the elements of the array ia[] with values of the variable
i.?
public class Lin{
public static void main(String argv[]){
Lin l = new Lin();
l.amethod();
}
public void amethod(){
int ia[] = new int[4];
//Start For loop
{
ia[i]=i;
System.out.println(ia[i]);
}
}}
1) for(int i=0; i < ia.length(); i++)
2) for (int i=0; i<
ia.length(); i++)
3) for(int i=1; i < 4; i++)
4) for(int i=0; i<
ia.length;i++)
What will be the result when you try to compile and run the following
code?
private class Base{
Base(){
int i = 100;
System.out.println(i);
}
}
public class Pri extends Base{
static int i = 200;
public static void main(String argv[]){
Pri p = new Pri();
System.out.println(i);
}
}
1) Error at compile time
2) 200
3) 100 followed by 200
4) 100
What will the following code print out?
public class Oct{
public static void main(String argv[]){
Oct o = new Oct();
o.amethod();
}
public void amethod(){
int oi= 012;
System.out.println(oi);
}
}
1)12
2)012
3)10
4)10.0
What will happen when you try compiling and running this code?
public class Ref{
public static void main(String argv[]){
Ref r = new Ref();
r.amethod(r);
}
public void amethod(Ref r){
int i=99;
multi(r);
System.out.println(i);
}
public void multi(Ref r){
r.i = r.i*2;
}
}
1) Error at compile time
2) An output of 99
3) An output of 198
4)
An error at runtime
You need to create a class that will store a unique object elements. You do not need to sort these elements but they must be unique.
What interface might be most suitable to meet this need?
1)Set
2)List
3)Map
4)Vector
Which of the following will successfully create an instance
of the Vector class and add an element?
1) Vector v=new
Vector(99);
v[1]=99;
2) Vector v=new Vector();
v.addElement(99);
3) Vector v=new Vector();
v.add(99);
4 Vector v=new Vector(100);
v.addElement("99");
You have created a simple Frame and overridden the paint method as follows
public void paint(Graphics g){
g.drawString("Dolly",50,10);
}
What will be the result when you attempt to compile and
run the program?
1) The string "Dolly" will be displayed at the centre of the frame
2) An
error at compilation complaining at the signature of the paint method
3) The
lower part of the word Dolly will be seen at the top of the form, with the top
hidden.
4) The string "Dolly" will be shown at the bottom of the form
What will be the result when you attempt to compile this program?
public class Rand{
public static void main(String argv[]){
int iRand;
iRand = Math.random();
System.out.println(iRand);
}
}
1) Compile time error referring to a cast problem
2) A random number
between 1 and 10
3) A random number between 0 and 1
4) A compile time
error about random being an unrecognised method
Given the following code
import java.io.*;
public class Th{
public static void main(String argv[]){
Th t = new Th();
t.amethod();
}
public void amethod(){
try{
ioCall();
}catch(IOException ioe){}
}
}
What code would be most likely for the body of the ioCall method
1) public void ioCall ()throws IOException{
DataInputStream din = new DataInputStream(System.in);
din.readChar();
}2) public void ioCall ()throw IOException{
DataInputStream din = new DataInputStream(System.in);
din.readChar();
}3) public void ioCall (){
DataInputStream din = new DataInputStream(System.in);
din.readChar();
}4) public void ioCall throws IOException(){
DataInputStream din = new DataInputStream(System.in);
din.readChar();
}
What will happen when you compile and run the following code?
public class Scope{
private int i;
public static void main(String argv[]){
Scope s = new Scope();
s.amethod();
}//End of main
public static void amethod(){
System.out.println(i);
}//end of amethod
}//End of class
1) A value of 0 will be printed out
2) Nothing will be printed out
3) A
compile time error
4) A compile time error complaining of the scope of the
variable i
You want to lay out a set of buttons horizontally but
with more space between the first button and the rest. You are going to use the
GridBagLayout manager to control the way the buttons are set
out. How will you modify the way the GridBagLayout acts in order to change the
spacing around the first button?
1) Create an instance of the GridBagConstraints class, call the weightx()
method and then pass the GridBagConstraints instance with the component to the
setConstraints method of the GridBagLayout class.
2) Create an instance of the GridBagConstraints class, set the weightx field and then pass the GridBagConstraints instance with the component to the setConstraints method of the GridBagLayout class.
3) Create an instance of the GridBagLayout class, set the weightx field and then call the setConstraints method of the GridBagLayoutClass with the component as a parameter.
4) Create an instance of the GridBagLayout class, call the setWeightx() method and then pass the GridBagConstraints instance with the component to the setConstraints method of the GridBagLayout class.
Which of the following can you perform using the File
class?
1) Change the current directory
2) Return the name of the parent
directory
3) Delete a file
4) Find if a file contains text or binary
information
Which of the following code fragments will compile without error
1)
public void paint(Graphics g){
int polyX[] = {20,150,150};
int polyY[]= {20,20,120};
g.drawPolygon(polyX, polyY,3);
}2)
public void paint(Graphics g){
int polyX[] = {20,150,150};
int polyY[]= {20,20,120};
g.drawPolygon(polyX, polyY);
}3)
public void paint(Graphics g){
int polyX[3] = {20,150,150};
int polyY[3]= {20,20,120};
g.drawPolygon(polyX, polyY,3);
}4)
public void paint(Graphics g){
int polyX[] = {20,150,150};
int polyY[]= {20,20,120};
drawPolygon(polyX, polyY);
}
You are concerned about that your program may attempt to use more memory than is available. To avoid this situation you want to ensure that the Java Virtual Machine will run its garbage collection just before you start a complex routine. What can you do to be certain that garbage collection will run when you want .
1) You cannot be certain when garbage collection will run
2) Use the
Runtime.gc() method to force garbage collection
3) Ensure that all the
variables you require to be garbage collected are set to null
4) Use the
System.gc() method to force garbage collection
You are using the GridBagLayout manager to place a series of buttons on a Frame. You want to make the size of one of the buttons bigger than the text it contains. Which of the following will allow you to do that?
1) The GridBagLayout manager does not allow you to do this
2) The setFill
method of the GridBagLayout class
3) The setFill method of the
GridBagConstraints class
4) The fill field of the GridBagConstraints
class
Which of the following most closely describes a bitset collection?
1) A class that contains groups of unique sequences of bits
2) A method
for flipping individual bits in instance of a primitive type
3) An array of
boolean primitives that indicate zeros or ones
4) A collection for storing
bits as on-off information, like a vector of bits
You have these files in the same directory. What will
happen when you attempt to compile and run Class1.java if you have not already
compiled Base.java
//Base.java
package Base;
class Base{
protected void amethod(){
System.out.println("amethod");
}//End of amethod
}//End of class basepackage Class1;
//Class1.java
public class Class1 extends Base{
public static void main(String argv[]){
Base b = new Base();
b.amethod();
}//End of main
}//End of Class1
1) Compile Error: Methods in Base not found
2) Compile Error: Unable to
access protected method in base class
3) Compilation followed by the output
"amethod"
4)Compile error: Superclass Class1.Base of class Class1.Class1 not
found
answer to
Question 58
What will happen when you attempt to compile and run the following code
class Base{
private void amethod(int iBase){
System.out.println("Base.amethod");
}
}
class Over extends Base{
public static void main(String argv[]){
Over o = new Over();
int iBase=0;
o.amethod(iBase);
}
public void amethod(int iOver){
System.out.println("Over.amethod");
}
}
1) Compile time error complaining that Base.amethod is private
2) Runtime
error complaining that Base.amethod is private
3) Output of
Base.amethod
4) Output of Over.amethod()
You are creating an applet with a Frame that contains buttons. You are using the GridBagLayout manager and you have added Four buttons. At the moment the buttons appear in the centre of the frame from left to right. You want them to appear one on top of the other going down the screen. What is the most appropriate way to do this.
1) Set the gridy value of the GridBagConstraint class to a value
increasing from 1 to 4
2) set the fill value of the GridBagConstrint class to
VERTICAL
3) Set the ipady value of the GridBagConstraint class to a value
increasing from 0 to 4
4) Set the fill value of the GridBagLayout class to
GridBag.VERTICAL
Back to
question 1)
Objective 2.6
5) int i=10;
explanation:
1) float f=1.3;
Will not compile because the default
type of a number with a floating point component is a double. This would compile
with a cast as in
float f=(float) 1.3
2) char c="a";
Will not compile because a char (16 bit unsigned integer) must be defined with single quotes. This would compile if it were in the form
char c='a';
3) byte b=257;
Will not compile because a byte is eight bits. Take of one bit for the sign component you can define numbers between
-127 to +127
4) a boolean value can either be true of false, null is not allowed.
Objective 3.1
1) Can't make static reference to void amethod.
Because main is defined as static you need to create an instance of the class
in order to call any non-static methods. Thus a typical way to do this would be.
MyClass m=new MyClass();
m.amethod();
Answer 2 is an attempt to confuse because the convention is for a main method to be in the form
String argv[]
That argv is just a convention and any acceptable identifier for a string
array can be used. Answers 3 and 4 are just nonsense.
back to
Question 3)
Objective 1.2
2 and 3 will compile without error.
1 will not compile because any package declaration must come before any other code. Comments may appear anywhere.
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question 4)
Objective 1.9)
1) A byte is a signed 8 bit integer.
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question 5)
Objective 1.4)
4) Exception raised: "java.lang.ArrayIndexOutOfBoundsException: 2"
Unlike C/C++ java does not start the parameter count with the program name. It does however start from zero. So in this case zero starts with good, morning would be 1 and there is no parameter 2 so an exception is raised.
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question 6)
Objective 1.5)
1) if
3) goto
4) while
5) case
then is not a Java keyword, though if you are from a VB background you might think it was. Goto is a reserved word in Java.
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Question 7)
Objective 1.10)
2) variable2
3) _whatavariable
4) _3_
5) $anothervar
An identifier can begin with a letter (most common) or a dollar sign($) or an
underscore(_). An identifier cannot start with anything else such as a number, a
hash, # or a dash -. An identifier cannot have a dash in its body, but it may
have an underscore _. Choice 4) _3_ looks strange but it is an acceptable, if
unwise form for an identifier.
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Question 8)
Objective 1.6)
4) 0
Class level variables are always initialised to default values. In the case of an int this will be 0. Method level variables are not given default values and if you attempt to use one before it has been initialised it will cause the
Error Variable i may not have been initialized
type of error.
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Question 9)
Objective 1.7,3.4)
3 ) 2
No error will be triggered.
Like in C/C++, arrays are always referenced from 0. Java allows an array to
be populated at creation time. The size of array is taken from the number of
initializers. If you put a size within any of the square brackets you will get
an error.
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question 10)
Objective 1.7)
3) 0
Arrays are always initialised when they are created. As this is an array of
ints it will be initalised with zeros.
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Question 11)
Objective 3.6
3) Error Mine must be declared abstract
A class that contains an abstract method must itself be declared as abstract.
It may however contain non abstract methods. Any class derived from an abstract
class must either define all of the abstract methods or be declared abstract
itself.
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Question 12)
Objective 4.1)
3) one, two, default
Code will continue to fall through a case statement until it encounters a break.
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Question 13)
Objective 4.1)
2) default, zero
Although it is normally placed last the default default statement does not have to be the last item as you fall through the case bock Because there is no case label found matching the expression the default label is executed and the code continues to fall through until it encounters a break.
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Question 14)
Objective 4.2,
2,3
Example 1 will not compile because if must always test a boolean. This can
catch out C/C++ programmers who expect the test to be for either 0 or not 0.
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Question 15)
Objective 4.5)
3) No such file found, doing finally, -1
The no such file found message is to be expected, however you can get caught out if you are not aware that the finally clause is almost always executed, even if there is a return statement.
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Question 16)
Objective Unknown
4) code, height, width
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Question 17)
Objective 5.8 (sort of)
3) Runtime Exception
Without the cast to sub you would get a compile time error. The cast tells
the compiler that you really mean to do this and the actual type of b does not
get resolved until runtime. Casting down the object hierarchy as the compiler
cannot be sure what has been implemented in descendent classes. Casting up is
not a problem because sub classes will have the features of the base classes.
This can feel counter intuitive if you are aware that with primitives casting is
allowed for widening operations (ie byte to int).
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question 18)
Objective unknown
3) null
If a parameter is not available the applet will still run, but any attempt to
access the parameter will return a null.
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Question 19)
Objective 1.1)
3) Move up the hierarchy in the HTML documentation to locate methods in base
classes
The documentation created by JavaDoc is based on tags placed into the
sourcecode. The convention for documentation is that methods and fields of
ancestors are not duplicated in sub classes. So if you are looking for something
and it does not appear to be there, you move up the class hierarchy to find it.
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Question 20)
Objective 10.4)
3) One button occupying the entire frame saying Bye
The default layout manager for a Frame is a border layout. If directions are not given (ie North, South, East or West), any button will simply go in the centre and occupy all the space. An additional button will simply be placed over the previous button. What you would probably want in a real example is to set up a flow layout as in
setLayout(new FlowLayout()); which would.
Applets and panels have a default FlowLayout manager
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Question 21)
Objective 4.4)
1,2
Value for i=1 Value for j=1
Value for i=2 Value for j=1
The statement continue outer causes the code to jump to the label outer and
the for loop increments to the next number.
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Question 22)
Objective 9.5)
3) An arc bounded by a box of height 50, width 50, with a top left at
coordinates of 45,
90, starting at 90 degrees and traversing through 180
degrees counter clockwise.
fillArc(int x, int y, int width, int height, int startDegrees, int arcDegrees)
The fillArc function draws an arc in a box with a top left at coordinates X
& Y.
If the ArcDegrees is a positive number the arc is drawn counter
clockwise.
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Question 23)
Objective 4.7)
2,4
Options 1, & 4 will not compile as they attempt to throw Exceptions not
declared in the base class. Because options 2 and 4 take a parameter of type
long they represent overloading not overriding and there is no such limitations
on overloaded methods.
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Question 24)
Objective 8.1)
3) System.out.println(Math.ceil(-4.7));
Options 1 and 2 will produce -5 and option 4 will not compile because the Min method requires 2 parameters.
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Question 25
Objective 2.2
3) Error: Cant convert java lang Integer
The wrapper classes cannot be used like primitives.
Wrapper classes have similar names to primitives but all start with upper
case letters.
Thus in this case we have int as a primitive and Integer as a
wrapper. The objectives do not specifically mention the wrapper classes but
don't be surprised if they come up.
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Question 26)
Objective 8.2)
2) ic
This is a bit of a catch question. Anyone with a C/C++ background would
figure out that addressing in strings starts with 0 so that 1 corresponds to i
in the string Bicycle. The catch is that the second parameter returns the
endcharacter minus 1. In this case it means instead of the "icy" being returned
as intuition would expect it is only "ic".
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Question 27)
Objective 8.2)
3) s.indexOf('v');
charAt returns the letter at the position rather than searching for a letter
and returning the position, MID is just to confuse the Basic Programmers,
indexOf(s,'v'); is how some future VB/J++ nightmare hybrid, might perform such a
calculation.
Objective 2.2
1) s3=s1 + s2;
Java does not allow operator overloading as in C++, but for the sake of convenience the + operator is overridden for strings.
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Question 29)
Objective 2.5)
4) 7
The | is known as the Or operator, you could think of it as the either/or operator. Turning the numbers into binary gives
4=100
3=011
For each position, if either number contains a 1 the result will contain a result in that position. As every position contains a 1 the result will be
111
Which is decimal 7.
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Question 30
Objective 3.7)
1,2,3
public, private, static are all legal access modifiers for this inner class.
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Question 31
Objective 9.6)
Opening an image file requires an Image object, The Image class has no constructor that takes the name of an image file . For an application (rather than an applet) an image is created using the Toolkit class as in option 2.
2) Image image=Toolkit.getDefaultToolkit().getImage("MyPicture.jpg");
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Question 32)
Objective 1.3)
2) setLayout(new GridLayout(2,2));
Changing the layout manager is the same for an Applet or an application. Answer 1 is wrong and implausible as a standard method is unlikely to have a name as long as setLayoutManager. Answers 3 and 4 are incorrect because changing the layout manager always requires an instance of one of the Layout Managers and these are bogus methods.
Instead of creating the anonymous instance of the Layout manager as in option
2 you can also create a named instance and pass that as a parameter. This is
often what automatic code generators such as Borland/Inprise JBuilder do.
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Question 33)
Objective 7.2)
3) The code will cause an error at compile time
The error is caused because run should have a void not an int return type.
Any class that is implements an interface must create a method to match all of the methods in the interface. The Runnable interface has one method called run that has a void return type.The sun compiler gives the error
Method redefined with different return type: int run() was defined as void
run();
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Question 34)
Objective 11.1)
2) public void update(Graphics g) {
paint(g);
}
If not overridden the update method clears the background and calls paint(); By overriding the update method, any previously drawn graphics will not be cleared. This is only a trivial way of preserving any graphics drawn. If the application is resized or the drawing area covered in some way the graphics will be cleared.
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Question 35
Objective 2.2
4) Compile time error
The only operator overloading offered by java is the + sign for the String class. A char is a 16 bit integer and cannot be concatenated to a string with the + operator.
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Question 36
Objective 8.2)
3) if(s.equalsIgnoreCase(s2))
String comparison is case sensitive so using the equals string method will
not return a match. Using the==operator just compares where memory address of
the references and noCaseMatch was just something I made up to give me a fourth
slightly plausible option.
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Question 37
Objective 9.1)
1) s.setBackground(Color.pink);
For speakers of the more British spelt English note that there is no letter u in Color. Also the constants for colors are in lower case.
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Question 38)
Objective 13.1)
4) The File class does not support directly changing the current directory.
This seems rather surprising to me, as changing the current directory is a very common requirement. You may be able to get around this limitation by creating a new instance of the File class passing the new directory to the constructor as the path name.
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Question 39)
Objective 9.2)
1)With a fixed font you will see 5 characters, with a proportional it will depend on the width of the characters
With a proportional font the letter w will occupy more space than the letter i. So if you have all wide characters you may have to scroll to the right to see the entire text of a TextField.
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Question 40)
Objective 5.8
3) On the line After //Two put super(10);
Constructors can only be invoked from within constructors.
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Question 41)
Objective 2.8)
3) 10 and 40
when a parameter is passed to a method the method receives a copy of the value. The method can modify its value without affecting the original copy. Thus in this example when the value is printed out the method has not changed the value.
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Question 42
Objective 3.3
4) for(int i=0; i< ia.length;i++)
Although you could control the looping with a literal number as with the number 4 used in sample 3, it is better practice to use the length property of an array. This provides against bugs that might result if the size of the array changes. This question also checks that you know that arrays starts from zero and not One.
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Question 43)
Objective 3.6 (maybe)
1) Error at compile time
This is a slightly sneaky one as it looks like a question about constructors, but it is attempting to test knowledge of the use of the private modifier. A top level class cannot be defined as private. If you didn't notice the modifier private, remember in the exam to be real careful to read every part of the question.
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Question 44
Objective 1.11)
3)10
The name of the class might give you a clue with this question, Oct for Octal. Prefixing a number with a zero indicates that it is in Octal format. Thus when printed out it gets converted to base ten. 012 in octal means the first column from the right has a value of 2 and the next along has a value of one times eight. In decimal that adds up to 10.
Objective 3.5)
1) Error at compile time
The variable i is created at the level of amethod and will not be available inside the method multi.
Java2 Objective 10.1)
1) Set
The Set interface ensures that its elements are unique, but does not order the elements. In reality you probably wouldn't create your own class using the Set interface. You would be more likely to use one of the JDK classes that use the Set interface such as ArraySet.
Java2 Objective 10.1)
4) Vector v=new Vector(100);
v.addElement("99")
A vector can only store objects not primitives. The parameter "99" for the addElement method pases a string object to the Vector. Option 1) creates a vector OK but then uses array syntax to attempt to assign a primitive. Option 2 also creates a vector then uses correct Vector syntax but falls over when the parameter is a primitive instead of an object. Option 3 compounds the errors by using the fictitious add method.
Objective 9.5)
3) The lower part of the word Dolly will be seen at the top of the form
The Second parameter to the drawstring method indicates where the baseline of the string will be placed. Thus the 3rd parameter of 10 indicates the Y coordinate to be 10 pixels from the top of the Frame. This will result in just the bottom of the string Dolly showing up or possibly only the descending part of the letter y.
Objective 8.1)
1) Compile time error referring to a cast problem
This is a bit of a sneaky one as the Math.random method returns a pseudo random number between 0 and 1, and thus option 3 is a plausible answer. However the number returned is a double and so the compiler will complain that a cast is needed to convert a double to an int.
Objective 4.6)
1) public void ioCall ()throws IOException{
DataInputStream din = new DataInputStream(System.in);
din.readChar();
}
If a method might throw an exception it must either be caught within the method with a try/catch block, or the method must indicate the exception to any calling method by use of the throws statement in its declaration. Without this, an error will occur at compile time.
Objective 3.10)
3) A compile time error
Because only one instance of a static method exists not matter how many instance of the class exists it cannot access any non static variables. The JVM cannot know which instance of the variable to access. Thus you will get an error saying something like
Can't make a static reference to a non static variable
Java2 Objective 8.2)
2) Create an instance of the GridBagConstraints class, set the weightx
field and then pass the GridBagConstraints instance with the component to the
setConstraints method of the GridBagLayout class.
The Key to using the GridBagLayout manager is the GridBagConstraint
class. This class is not consistent with the general naming conventions in the
java API as you would expect that weightx would be set with a method,
whereas it is a simple field (variable).
Objective 13.1)
2) Return the name of the parent directory
3) Delete a file
It is surprising that you can't change the current directory. If you need to do this, the best way seems to be to create a new instance of the File class and pass the new directory to the constructor. It is not so surprising that you can't tell if a file contains text or binary information.
Objective 9.5)
1)
public void paint(Graphics g){
int polyX[] = {20,150,150};
int polyY[]= {20,20,120};
g.drawPolygon(polyX, polyY,3);
}
Drawpolygon takes three parameters, the first two are arrays of the X,Y coordinates and the final is n integer specifying the number of vertices (whatever they are).
Objective 6.1)
1) You cannot be certain when garbage collection will run
Although there is a Runtime.gc(), this only suggests that the Java Virtual Machine does its garbage collection. You can never be certain when the garbage collector will run. Roberts and Heller is more specific abou this than Boone. This uncertainty can cause consternation for C++ programmers who wish to run finalize methods with the same intent as they use destructor methods.
Java2 Objective 8.2)
4) The fill field of the GridBagConstraints class
Unlike the GridLayout manager you can set the individual size of a control such as a button using the GridBagLayout manager. A little background knowledge would indicate that it should be controlled by a setSomethingOrOther method, but it isn't.
Java2 Objective 10.1)
4) A collection for storing bits as on-off information, like a vector of bits
This is the description given to a bitset in Bruce Eckels "Thinking in Java" book. The reference to unique sequence of bits was an attempt to mislead because of the use of the word Set in the name bitset. Normally something called a set implies uniqueness of the members, but not in this context.
Objective 3.10)
4)Compile error: Superclass Class1.Base of class Class1.Class1 not found
Using the package statement has an effect similar to placing a source file into a different directory. Because the files are in different packages they cannot see each other. The stuff about File1 not having been compiled was just to mislead, java has the equivalent of an "automake", whereby if it was not for the package statements the other file would have been automatically compiled.
Objective 5.3)
4) Output of Over.amethod()
The names of parameters to an overridden method is not important.
Java2 Objective 8.2)
1) Set the gridy value of the GridBagConstraint class to a value increasing from 1 to 4
Answer 4 is fairly obviously bogus as it is the GridBagConstraint class that does most of the magic in laying out components under the GridBagLayout manager. The fill value of the GridBagConstraint class controls the behavior inside its virtual cell and the ipady field controls the internal padding around a component.