Java Certification Question 0050

Given the following code

public class Sytch{

int x=2000;

public static void main(String argv[]){

System.out.println("Ms "+argv[1]+"Please pay $"+x);

}

}

What will happen if you attempt to compile and run this code with the command line

java Sytch Jones Diggle

1) Compilation and output of Ms Diggle Please pay $2000
2) Compile time error
3) Compilation and output of Ms Jones Please pay $2000
4) Compilation but runtime error

Answer 2:

2) Compile time error

The main method is static and cannot access the non static variable x

Java Certification Question 0049

Which of the following statements are true?

1) The automatic garbage collection of the JVM prevents programs from ever running out of memory
2) A program can suggest that garbage collection be performed but not force it
3) Garbage collection is platform independent
4) An object becomes eligible for garbage collection when all references denoting it are set to null.

Answers 2 and 4:

2) A program can suggest that garbage collection be performed but not force it
4) A reference becomes eligable for garbage collection when it is assigned to null

If a program keeps creating new references without any being discarded it may run out of memory. Unlike most aspects of Java garbage collection is platform dependent.

Java Certification Question 0048

Which of the following statements are true?

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

Answer 1:

1) Static methods cannot be overriden to be non static

The JDK1.1 compiler will issue an error message "static methods cannot be overriden" if you atempt to do this. There is no logic or reason why private methods should not be overloaded or that static methods should not be declared private. Option 4 is a jumbled up version of the limitations of exceptions for overriden methods

Java Certification Question 0047

What will happen when you attempt to compile and run the following code?

class Base{

Base(){

System.out.println("Base");

}

}

public class Checket extends Base{

public static void main(String argv[]){

Checket c = new Checket();

super();

}

Checket(){

System.out.println("Checket");

}

}

1) Compile time error
2) Checket followed by Base
3) Base followed by Checket
4) runtime error

Answer 1:

1) Compile time error

With the sun JDK it will produce the following error

"Only constructors can invoke constructors".

If you took out the call to super that causes this error the program would compile and at runtime it would output Base and then Checket as constructors are called from the oldest ancestor class downwards.

Java Certification Question 0046

Which of the following statements are true?

1) A method cannot be overloaded to be less public in a child class
2) To be overridden a method must have the same name and parameter types
3) To be overridden a method must have the same name, parameter and return types
4) An overridden method must have the same name, parameter names and parameter types

Answer 3:

3) To be overriden a method must have the same name, parameter and return types

Option 1 is a sneaky one in that it should read overriden not overloaded. An overriden method must also have the same return type. Parameter names are purely a programmer convenience and are not a factor in either overloading and overriding. Parameter order is a factor however.

Java Certification Question 0045

What will happen when you attempt to compile and run the following code?

public class Sandys{

private int court;

public static void main(String argv[]){

Sandys s = new Sandys(99);

System.out.println(s.court);

}

Sandys(int ballcount){

court=ballcount;

}

}

1) Compile time error, the variable court is defined as private
2) Compile time error, s is not initialized when the System.out method is called
3) Compilation and execution with no output
4) Compilation and run with an output of 99

Answer 4:

4) Compilation and run with an output of 99

The fact that the variable court is declared as private does not stop the constructor from being able to initialise it.

Java Certification Question 0044

Given a reference called

t

to to a class which extends Thread, which of the following will cause it to give up cycles to allow another thread to execute.

1) t.yield();
2) yield()
3) yield(100) //Or some other suitable amount in milliseconds
4) yield(t);

Answer :

yield is a static method inherited from Thread and causes whatever thread is currently executing to yield its cycles.

2) yield()

Java Certification Question 0043

Which of the following statements are true

1) constructors cannot be overloaded
2) constructors cannot be overridden
3) a constructor can return a primitive or an object reference
4) constructor code executes from the current class up the hierarchy to the ancestor class

Answer 2: constructors cannot be overriden

Overloading constructors is a key technique to allow multiple ways of initialising classes. By definition constructors have no return values so option 3 makes no sense. Option 4 is the inverse of what happens as constructor code will execute starting from the oldest ancestor class downwards. You can test this by writing a class that inherits from a base class and getting the constructor to print out a message. When you create the child class you will see the order of constructor calling.

Java Certification Question 0042

Given the following declaration

Integer i=new Integer(99);

How can you now set the value of i to 10?

1) i=10;
2) i.setValue(10);
3) i.parseInt(10);
4) none of the above

Answer 4: none of the above

The wrapper classes are immutable. Once the value has been set it cannot be changed. A common use of the wrapper classes is to take advantage of their static methods such as Integer.parseInt(String s) that will returns an integer if the String contains one.

Java Certification Question 0041

You are creating an application that has a form with a text entry field used to enter a persons age. Which of the following is appropriate for capturing this information.

1) Use the Text field of a TextField and parse the result using Integer
2) Use the getInteger method of the TextField
3) Use the getText method of a TextBox and parse the result using the getInt method of Integer class
4) Use the getText method of a TextField and use the parseInt method of the Integer class

Answer 4: Use the getText method of a Textfield and use the parseInt method of the Integer class

Here is an example of how you might do this

Integer.parseInt(txtInputValue.getText());

I'm not sure that a question on this actually will come up in the exam but it is a very useful thing to know in the real world.

Java Certification Question 0040

Given the following code

class Base{
static int oak=99;
}

public class Doverdale extends Base{

public static void main(String argv[]){
Doverdale d = new Doverdale();
d.amethod();
}
public void amethod(){
//Here
}
}

Which of the following if placed after the comment //Here, will compile and modify the value of the variable oak?
1) super.oak=1;
2) oak=33;
3) Base.oak=22;
4) oak=50.1;



Answer :
1) super.oak=1;
2) oak=33;
3) Base.oak=22;
Because the variable oak is declared as static only one copy of it will exist. Thus it can be changed either through the name of its class or through the name of any instance of that class. Because it is created as an integer it canot be assigned a fractional component without a cast.

Java Certification Question 0039

Given the following class definition
public class Droitwich{

class one{
private class two{
public void main(){
System.out.println("two");
}
}
}
}

Which of the following statements are true

1) The code will not compile because the classes are nested to more than one level
2) The code will not compile because class two is marked as private
3) The code will compile and output the string two at runtime
4) The code will compile without error



Answer :
4) The code will compile without error
There are no restrictions on the level of nesting for inner/nested classes. Inner classes may be marked private. The main method is not declared as public static void main, and assuming that the commandline was java Droitwich it would not be invoked anyway.

Java Certification Question 0038

Which of the following statements are true?
1) Code must be written to cause a frame to close on selecting the system close menu
2) The default layout for a Frame is the BorderLayout Manager
3) The layout manager for a Frame cannot be changed once it has been assigned
4) The GridBagLayout manager makes extensive use of the the GridBagConstraints class.



Answer :
1) Code must be written to cause a frame to close on selecting the system close menu
2) The default layout for a Frame is the BorderLayout Manager
4) The GridBagLayout manager makes extensive use of the the GridBagConstraints class.
You can change the layout manager for a Frame or any other container whenever you like.

Java Certification Question 0037

Given the following class definition
public class Upton{

public static void main(String argv[]){

}

public void amethod(int i){}
//Here
}

Which of the following would be legal to place after the comment //Here ?
1) public int amethod(int z){}
2) public int amethod(int i,int j){return 99;}
3) protected void amethod(long l){ }
4) private void anothermethod(){}



Answer:
2) public int amethod(int i, int j) {return 99;}
3) protected void amethod (long l){}
4) private void anothermethod(){}
Option 1 will not compile on two counts. One is the obvious one that it claims to return an integer. The other is that it is effectivly an attempt to redefine a method within the same class. The change of name of the parameter from i to z has no effect and a method cannot be overriden within the same class.

Java Certification Question 0036

Assuming any exception handling has been set up, which of the following will create an instance of the RandomAccessFile class
1) RandomAccessFile raf=new RandomAccessFile("myfile.txt","rw");
2) RandomAccessFile raf=new RandomAccessFile( new DataInputStream());
3) RandomAccessFile raf=new RandomAccessFile("myfile.txt");
4) RandomAccessFile raf=new RandomAccessFile( new File("myfile.txt"));



Answer :
1) RandomAccessFile raf=new RandomAccessFile("myfile.txt","rw");
The RandomAccessFile is an anomaly in the Java I/O architecture. It descends directly from Object and is not part of the Streams architecture.

Java Certification Question 0035

What will happen when you attempt to compile and run the following code

public class Borley extends Thread{

public static void main(String argv[]){
Borley b = new Borley();
b.start();
}

public void run(){
System.out.println("Running");
}
}

1) Compilation and run but no output
2) Compilation and run with the output "Running"
3) Compile time error with complaint of no Thread target
4) Compile time error with complaint of no access to Thread package



Answer :
2) Compilation and run with the output "Running"
This is perfectly legitimate if useless sample of creating an instnace of a Thread and causing its run method to execute via a call to the start method. The Thread class is part of the core java.lang package and does not need any explicit import statement. The reference to a Thread target is an attempt to mislead with a reference to the method of using the Runnable interface instead of simply inheriting from the Thread super class.

Java Certification Question 0034

What will happen when you attempt to compile and run the following code?

import java.io.*;

class ExBase{
abstract public void martley(){
}
}

public class MyEx extends ExBase{

public static void main(String argv[]){
DataInputStream fi = new DataInputStream(System.in);
try{
fi.readChar();
}catch(IOException e){
System.exit(0);
}
finally {System.out.println("Doing finally");}
}
}

1) Compile time error
2) It will run, wait for a key press and then exit
3) It will run, wait for a keypress, print "Doing finally" then exit
4) At run and immediately exit



Answer :
1) Compile time error
It wil produce an error like "Abstract and native method can't have a body. This is typical of the more misleading question where you might think it is asking you about the circumstances under which the finally clause runs, but actually it is about something else.

Java Certification Question 0033

Which of the following statements are true?
1) Java uses a system called UTF for I/O to support international character sets
2) The RandomAccessFile is the most suitable class for supporting international character sets
3) An instance of FileInputStream may not be chained to an instance of FileOutputStream
4) File I/O activities requires use of Exception handling



Answer :
1) Java uses a system called UTF for I/O to support international character sets
3) An instance of FileInputStream may not be chained to an instance of FileOutputStream
4) File I/O activities requires use of Exception handling
Internally Java uses Unicode which are 16 bit characters. For I/O Java uses UTF which may be more thatn 16 bits per character.
Generally InputStreams can only be chained to other InputStreams and OutputStreams can only be chained to other OutputStreams. The piped streams are an exception to this.

Java Certification Question 0032

Which of the following statements are true about a variable created with the static modifier?

1) Once assigned the value of a static variable may not be altered
2) A static variable created in a method will keep the same value between calls
3) Only one instance of a static variable will exist for any amount of class instances
4) The static modifier can only be applied to a primitive value



Answer :
3) Only one instance of a static variable will exist for any amount of class instances
Option 1) is more a description of a final variable. Option 2 is designed to fool Visual Basic programmers like me as this is how you can use the keyword static in VB. The modifier static can be applied to a class, method or variable.

Java Certification Question 0031

Which of the following statements are true?
1) The default layout manager for an Applet is FlowLayout
2) The default layout manager for a Frame is FlowLayout
3) A layout manager must be assigned to an Applet before the setSize method is called
4) The FlowLayout manager attempts to honor the preferred size of any components



Answer :
1) The default layout manager for an Applet is FlowLayout
4) The FlowLayout manager attempts to honor the preferred size of any components
The default layout manager fror an Application is BorderLayout. An applet will use the default of FlowLayout if one is not specifically applied.

Java Certification Question 0030

Which of the following statements are true?
1) The % is used to calculate a percentage thus: 10 % 20=50
2) The / operator is used to divide one value by another
3) The # symbol may not be used as the first character of a variable
4) The $ symbol may not be used as the first character of a variable



Answer :
2) The / operator is used to divide one value by another
3) The # symbol may not be used as the first character of a variable
The % is the modulo operator and returns the remainder after a division. Thus 10 % 3=1
The $ symbol may be used as the first character of a variable, but I would suggest that it is generally not a good idea. The # symbol cannot be used anywhere in the name of a variable. Knowing if a variable can start with the # or $ characters may seem like arbitrary and non essential knowlege but questions like this do come up on the exam.

Java Certification Question 0029

Which of the following most closely describes the process of overriding?
1) A class with the same name replaces the functionality of a class defined earlier in the hierarchy
2) A method with the same name completely replaces the functionality of a method earlier in the hierarchy
3) A method with the same name but different parameters gives multiple uses for the same method name
4) A class is prevented from accessing methods in its immediate ancestor



Answer :
2) A method with the same name completly replaces the functionality of a method earlier in the hierarchy
Option 3 is more like a description of overloading. I like to remind myself of the difference between overloading and overriding in that an overriden method is like something overriden in the road, it is squashed, flat no longer used and replaced by something else. An overloaded method has been given extra work to do (it is loaded up with work), but it is still being used in its original format. This is just my little mind trick and doesn't match to anything that Java is doing.

Java Certification Question 0028

You are given a class hierarchy with an instance of the class Dog. The class Dog is a child of mammal and the class Mammal is a child of the class Vertebrate. The class Vertebrate has a method called move which prints out the string "move". The class mammal overrides this method and prints out the string "walks". The class Dog overrides this method and prints out the string "walks on paws". Given an instance of the class Dog,. how can you access the ancestor method move in Vertebrate so it prints out the string "move";
1) d.super().super().move();
2) d.parent().parent().move();
3) d.move();
4) none of the above;



Answer :
4) none of the above;
You may access methods of a direct parent class through the use of super but classes further up the hierarchy are not visible.

Java Certification Question 0027

Given the following class
public class Ombersley{

public static void main(String argv[]){
boolean b1 = true;
if((b1 ==true) || place(true)){
System.out.println("Hello Crowle");
}
}

public static boolean place(boolean location){
if(location==true){
System.out.println("Borcetshire");
}
System.out.println("Powick");
return true;
}
}

What will happen when you attempt to compile and run it?

1) Compile time error
2) Output of "Hello Crowle"
3) Output of Hello Crowle followed by Borcetshire and Powick
4) No output



Answer :
2) Output of "Hello Crowle"
This code is an example of a short circuited operator. Because the first operand of the || (or) operator returns true Java sees no reason to evaluate the second. Whatever the value of the second the overall result will always be true. Thus the method called place is never called.

Java Certification Question 0026

Which of the following statements are true?
1) The elements in a Java array can only be of primitive types, not objects
2) Arrays are initialized to default values wherever they are created
3) An array may be dynamically resized using the setSize method
4) You can find out the size of an array using the size method



Answer :
2) Arrays are initialized to default values wherever they are created

You can find the size of an array using the length field. The method length is used to return the number of characters in a String. An array can contain elements of any type but they must all be of the same type. The size of an array is fixed at creation. If you want to change its size you can of course create a new array and assign the old one to it. A more flexible approach can be to use a collection class such as Vector.

Java Certification Question 0025

Which of the following statements are true?
1) The following statement will produce a result of 1. System.out.println( -1 >>>2);
2) Performing an unsigned left shift (<<<) on a negative number will always produce a negative number result
3) The following statement will produce a result of zero, System.out.println(1 >>1);
4) All the integer primitives in java are signed numbers



Answer :
3) The following statement will produce a result of zero, System.out.println(1 >>1);
Although you might not know the exact result of the operation -1 >>> 2 a knowledge of the way the bits will be shifted will tell you that the result is not plus 1. (The result is more like 1073741823 ) There is no such Java operator as the unsigned left shift. Although it is normally used for storing characters rather than numbers the char Java primitive is actually an unsigned integer type.

Java Certification Question 0024

Which of the following statements are true?
1) A method in an interface must not have a body
2) A class may extend one other class plus at most one interface
3) A class may extends at most one other class plus implement many interfaces
4) An class accesses an interface via the keyword uses



Answer :
1) A method in an interface must not have a body
3) A class may extends one other class plus many interfaces
A class accesses an interface using the implements keyword (not uses)

Java Certification Question 0023

Which of the following statements are true?
1 ) The String class is implemented as a char array, elements are addressed using the stringname[] convention
2) The + operator is overloaded for concatenation for the String class
3) Strings are a primitive type in Java and the StringBuffer is used as the matching wrapper type
4) The size of a string can be retrieved using the length property



Answer :
2) The + operator is overloaded for concatenation for the String class
In Java Strings are implemented as a class within the Java.lang package with the special distinction that the + operator is overloaded. If you thought that the String class is implemented as a char array, you may have a head full of C/++ that needs emptying. There is not "wrapper class" for String as wrappers are only for primitive types.
If you are surprised that option 4 is not a correct answer it is because length is a method for the String class, but a property for and array and it is easy to get the two confused.

Java Certification Question 0022

Which of the following statements are true?
1) All of the variables in an interface are implicitly static
2) All of the variables in an interface are implicitly final
3) All of the methods in an interface are implicitly abstract
4) A method in an interface can access class level variables



Answer :
1) All of the variables in an interface are implicitly static
2) All of the variables in an interface are implicitly final
3) All of the methods in an interface are implictly abstract
All the variables in an interface are implicitly static and final. Any methods in an interface have no body, so may not access any type of variable

Java Certification Question 0021

Which of the following statements are true?
1) The default constructor has a return type of void
2) The default constructor takes a parameter of void
3) The default constructor takes no parameters
4) The default constructor is not created if the class has any constructors of its own.



Answer :
3) The default constructor takes no parameters
4) The default constructor is not created if the class has any constructors of its own.
Option 1 is fairly obviously wrong as constructors never have a return type. Option 2 is very dubious as well as Java does not offer void as a type for a method or constructor.