Java Certification Question 0020

Which of the following are Java keywords?
1) sizeof
2) main
3) transient
4) volatile



Answer :
3) transient
4) volatile
Option 1, sizeof is designed to catch out the C/C++ programmers. Java does not have a sizeof keyword as the size of primitives should be consistent on all Java implementations. Although a program needs a main method with the standard signature to start up it is not a keyword. The real keywords are less commonly used and therefore might not be so familiar to you.

Java Certification Question 0019

Which of the following are true?
1) A component may have only one event listener attached at a time
2) An event listener may be removed from a component
3) The ActionListener interface has no corresponding Adapter class
4) The processing of an event listener requires a try/catch block



Answer :
2) An event listener may be removed from a component
3) The ActionListener interface has no corresponding Adapter class
A component may have multiple event listeners attached. Thus a field may need to respond to both the mouse and the keyboard, requiring multiple event handlers. The ActionListener has not matching Adapter class because it has only one method, the idea of the Adapter classes is to eliminate the need to create blank methods.

Java Certification Question 0018

Which of the following will compile without error?
1)
char c='1';
System.out.println(c>>1);
2)
Integer i=Integer("1");
System.out.println(i>>1);
3)
int i=1;
System.out.println(i<<<1);
4)
int i=1;
System.out.println(i<<1);



Answer :
1)
char c='1';
System.out.println(c>>1);
4)
int i=1;
System.out.println(i<<1);
Be aware that Integer (not the upper case I) is a wrapper class and thus cannot be treated like a primitive. The fact that option 1 will compile may be a surprise, but although the char type is normally used to store character types, it is actually an unsigned integer type. The reason option 3 does not compile is that Java has a >>> operator but not a <<< operator.

Java Certification Question 0017

Which of the following statements are true?
1) static methods do not have access to the implicit variable called this
2) A static method may be called without creating an instance of its class
3) A static method may not be overriden to be non-static
4) A static method may not be overloaded



Answer :
1) static methods do not have access to the implicit variable called this
2) A static method may be called without creating an instance of its class
3) a static may not be overriden to be non-static
The implicit variable this refers to the current instance of a class and thus and by its nature a static method cannot have access to it.

Java Certification Question 0016

What will happen when you attempt to compile and run the following class?
class Base{
Base(int i){
System.out.println("Base");
}
}

class Severn extends Base{
public static void main(String argv[]){
Severn s = new Severn();
}
void Severn(){
System.out.println("Severn");
}
}
1) Compilation and output of the string "Severn" at runtime
2) Compile time error
3) Compilation and no output at runtime
4) Compilation and output of the string "Base"



Answer :
2) Compile time error
An error occurs when the class Severn attempts to call the zero parameter constructor in the class Base Because the Base class has an integer constructor Java does not provide the "behind the scenes" zero parameter constructor.