Java Programmer Certification Mock Exam No 1

Last Updated 10 July 2000

This is my mock Exam No 1 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.software.u-net.com/getanswers.htm

If you obtained this exam from some other source please email me to let me know and check out the latest version at http://www.jchq.net/

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Questions

Question 1)

1) float f=1.3;
2) char c="a";
3) byte b=257;
4) boolean b=null;
5) int i=10;
 

Answer to Question 1

Question 2)

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]); 
        } 
}

Answer to Question 2

Question 3)

1)

import java.awt.*; 
package Mypackage; 
class Myclass {}

package MyPackage; 
import java.awt.*; 
class MyClass{}

/*This is a comment */ 
package MyPackage; 
import java.awt.*; 
class MyClass{}

Answer to Question 3

Question 4)

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

Answer to Question 4

Question 5)

java myprog good morning

public class myprog{ 
public static void main(String argv[])

{ 
System.out.println(argv[2]) 
}

}

Answer to Question 5

Question 6)

1) if
2) then
3) goto
4) while
5) case

Answer to Question 6

Question 7)

1) 2variable
2) variable2
3) _whatavariable
4) _3_
5) $anothervar
6) #myvar

Answer to Question 7

Question 8)

public class MyClass{ 
        static int i; 
        public static void main(String argv[]){ 
                System.out.println(i); 
                } 
}

Answer to Question 8

Question 9)

public class Q { 
        public static void main(String argv[]){ 
                int anar[]=new int[]{1,2,3};
                System.out.println(anar[1]); 
                } 
}

Answer to Question 9

Question 10)

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]); 
                } 
}

Answer to Question 10

Question 11)

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]); 
                        } 
}

Answer to Question 11

Question 12)

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"); 
        }

Answer to Question 12

Question 13)

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"); 
}

Answer to Question 13

Question 14)

1)

int i=0; 
if(i) { 
        System.out.println("Hello"); 
        }

boolean b=true; 
boolean b2=true; 
if(b==b2) { 
        System.out.println("So true"); 
        }

int i=1; 
int j=2; 
if(i==1|| j==2) 
        System.out.println("OK");

int i=1; 
int j=2; 
if(i==1 &| j==2) 
        System.out.println("OK");

Question 15)

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; 
        } 
}

Answer to Question 15

Question 16)

1) Methods cannot be overriden to be more private
2) Static methods cannot be overloaded
3) Private methods cannot be overloaded
4) An overloaded method cannot throw exceptions not checked in the base class

Answer to Question 16

Question 17)

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;
                }

}

Question 18)

1) System.out.println( -1 >>> 2);will output a result larger than 10
2) System.out.println( -1 >>> 2); will output a positive number
3) System.out.println( 2 >> 1); will output the number 1
4) System.out.println( 1 <<< 2); will output the number 4
 

Answer to Question 18

Question 19)

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

Answer to Question 19

Question 20)

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

Answer to Question 20

Question 21)

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); 
                    } 
        } 
}

Answer to Question 21

Question 22)

If g is a graphics instance what will the following code draw on the screen?.
 

g.fillArc(45,90,50,50,90,180);

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.

Answer to Question 22

Question 23)

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
}

Answer to Question 23

Question 24)

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));

Answer to Question 24

Question 25)

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);

Answer to Question 25

Question 26)

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));

Answer to Question 26

Question 27)

1) mid(2,s);
2) charAt(2);
3) s.indexOf('v');
4) indexOf(s,'v');

Answer  to Question 27

Question 28)

String s1=new String("Hello") 
String s2=new String("there"); 
String s3=new String();

1) s3=s1 + s2;
2) s3=s1-s2;
3) s3=s1 & s2;
4) s3=s1 && s2

Answer to Question 28

Question 29)

System.out.println(4 | 3);

1) 6
2) 0
3) 1
4) 7

Answer to Question 29

Question 30)

public class MyClass1 {

public static void main(String argv[]){ }

/*Modifier at XX */ class MyInner {}

}

1) public
2) private
3) static
4) friend

Answer to Question 30

Question 31)

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");

Answer to Question 31

Question 32)

1) setLayoutManager(new GridLayout());
2) setLayout(new GridLayout(2,2));
3) setGridLayout(2,2);
4) setBorderLayout();

Answer to Question 32

Question 33)

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

     return 1;
     }//End run 
}//End class

Answer to Question 33

Question 34)

1) Override repaint thus

public void repaint(Graphics g){ 
    paint(g); 
    }

public void update(Graphics g) { 
        paint(g); 
        }

4) Remove the drawing from the paint Method and place in the calling code

Answer to Question 34

Question 35)

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); 
    } 
}

Answer to Question 35

Question 36)

//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"); 
        }
     } 
}

Answer to Question 36

Question 37)

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);
        }
}

1)s.setBackground(Color.pink);
2)s.setColor(PINK);
3)s.Background(pink);
4)s.color=Color.pink

Answer to Question 37

Question 38)

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.

Answer to Question 38

Question 39)

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

Answer to Question 39

Question 40)

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
        }
}

Answer to Question 40

Question 41)

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;
        }
}

Answer to Question 41

Question 42)

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]);
           }
        }

}

Answer to Question 42

Question 43)

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);
        }
}

Answer to Question 43

Question 44)

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);
        }
}

Answer to Question 44

Question 45

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;
          }
}

Answer to Question 45

Question 46)

What interface might be most suitable to meet this need?

1)Set
2)List
3)Map
4)Vector
 

Answer to Question 46

Question 47)

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");

Answer to Question 47

Question 48)

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 frame, with the top hidden.
4) The string "Dolly" will be shown at the bottom of the frame.

Answer to Question 48

Question 49)

public class Rand{
public static void main(String argv[]){
        int iRand;
        iRand = Math.random();
        System.out.println(iRand);
        }
}

Answer to Question 49

Question 50)

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){}
        }
        
}

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();
        }

Question 51)

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

Answer to Question 51

Question 52)

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.

Answer to Question 52

Question 53)

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

Answer to Question 53

Question 54)

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);
  }

Question 55)

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

Answer to Question 55

Question 56)

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
 

Answer to Question 56

Question 57)

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

Answer to Question 57

Question 58)

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 base

package 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

Answer to Question 58

Question 59)

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");
        }

}

Answer to Question 59

Question 60)

1) Set the gridy value of the GridBagConstraint class to a value increasing from 1 to 4
2) set the fill value of the GridBagConstraint 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

Answer to Question 60

If you have a copy of the Roberts and Heller Java2 Guide that says the exam does not cover the GridBagLayout, this is an error. You can confirm this by looking at the online errata at

http://www.sybex.com/cgi-bin/rd_err_temp.pl?2463err.html

Answer 1)

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

-128 to +127

4) a boolean value can either be true of false, null is not allowed.

Answer 2)

Objective 4.1

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.

Answer 3)

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.

Answer 4)

1) A byte is a signed 8 bit integer.

Answer 5)

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.

Answer 6)

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.

Answer 7)

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.

Answer 8)

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

Answer 9)

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.

Answer 10)

3) 0

Arrays are always initialised when they are created. As this is an array of ints it will be initalised with zeros.

Answer 11)

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.

Answer 12)

3) one, two, default

Code will continue to fall through a case statement until it encounters a break.

Answer 13)

2) default, zero

Although it is normally placed last the default statement does not have to be the last item as you fall through the case block. 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.

Answer 14)

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.

Answer 15)

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.

Answer 16)

Objective

Back to Question 16)

1) Methods cannot be overriden to be more private

Static methods cannot be overriden but they can be overloaded. There is no logic or reason why private methods should not be overloaded. Option 4 is a jumbled up version of the limitations of exceptions for overriden methods

Answer 17)

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).

Answer 18)

1) System.out.println( -1 >>> 2);will output a result larger than 10
2) System.out.println( -1 >>> 2); will output a positive number
3) System.out.println( 2 >> 1); will output the number 1

You can test this with the following class

public class shift{
static int i=2;
public static void main(String argv[]){
        System.out.println( -1  >>> 2);
        System.out.println( -1  >>> 2);
        System.out.println( 2  >> 1);
        }
}

Because of the way twos complement number representation works the unsigned right shift operation means a small shift in a negative number can return a very large value so the output of option 1 will be much larger than 10.

The unsigned right shift places no significance on the leading bit that indicates the sign. For this shift the value 1 of the bit sign is replaced with a zero turning the result into a positive number for option 2.

Answer 19)

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.

Answer 20)

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 allow the buttons to both appear side by side, given the appropriate font and size.
Applets and panels have a default FlowLayout manager
 
 

Answer 21)

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.

Answer 22)

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.

Answer 23)

2,3

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.

Answer 24)

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.

Answer 25)

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.

Answer 26)

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".

Answer 27)

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.

Answer 28)

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.

Answer 29)

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.

Answer 30)

1,2,3

public, private, static are all legal access modifiers for this inner class.

Answer 31)

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");

Answer 32)

2) setLayout(new GridLayout(2,2));
 

Changing the layout manager is the same for an Applet or an application. Answer 1 is wrong though it might have been a reasonable name for the designers to choose. 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.

Answer 33)

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();

Answer 34)

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.

Answer 35)

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.

Answer 36)

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.

Answer 37)

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.

Answer 38)

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.

Answer 39)

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.

Answer 40)

3) On the line After //Two put super(10);

Constructors can only be invoked from within constructors.

Answer 41)

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.

Answer 42)

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 option 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 as option 3 starts from one. Remember that array length is a field and not a function like the string size method.

Answer 43)

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.

Answer 44)

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.

Answer 45)

1) Error at compile time

The variable i is created at the level of amethod and will not be available inside the method multi.

Answer 46)

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 HashSet or TreeSet.

Answer 47)

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.

Answer 48)

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.

Answer 49)

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.

Answer 50)

1) public void ioCall ()throws IOException{
        DataInputStream din = new DataInputStream(System.in);
        din.readChar();
        }

Answer 51)

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

Answer 52)

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).

If you have a copy of the Roberts and Heller Java2 Guide that says the exam does not cover the GridBagLayout, this is an error. You can confirm this by looking at the online errata at

http://www.sybex.com/cgi-bin/rd_err_temp.pl?2463err.html

Answer 53)

2) Return the name of the parent directory
3) Delete a file

It is surprising that you can't change the current directory. It is not so surprising that you can't tell if a file contains text or binary information.

Answer 54)

1)

public void paint(Graphics g){
  int polyX[] = {20,150,150};
  int polyY[]= {20,20,120};
  g.drawPolygon(polyX, polyY,3);
  }

Answer 55)

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.

Answer 56)

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.

If you have a copy of the Roberts and Heller Java2 Guide that says the exam does not cover the GridBagLayout, this is an error. You can confirm this by looking at the online errata at

http://www.sybex.com/cgi-bin/rd_err_temp.pl?2463err.html

Answer 57)

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.

Answer 58)

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.

Answer 59)

4) Output of Over.amethod()

The names of parameters to an overridden method is not important.

Answer 60)

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.

If you have a copy of the Roberts and Heller Java2 Guide that says the exam does not cover the GridBagLayout, this is an error. You can confirm this by looking at the online errata at

http://www.sybex.com/cgi-bin/rd_err_temp.pl?2463err.html

End of Document