Page 1:
SCJP questions 1-20
Page 2:
SCJP questions 21-40
Page 3: SCJP questions 41-53
- What is the output of the following program ?
public class CDummy
{
static int unu = 1;
public static void main(String args[])
{
System.out.println("CDummy.");
CDummy cd = new CDummy();
System.out.println(cd.unu);
System.out.println(unu);
System.out.println(CDummy.unu);
}
}
\/\/\/\/\/\/\/\/\/\/
Dummy.
1
1
1
- What is wrong with the following code ? (there is a logical not syntactical error)
public void coolFunction()
{
String tmp;
synchronized(tmp)
{
doSyncWork();
}
}
\/\/\/\/\/\/\/\/\/\/
The synchronization takes place on a local variable. This is
useless because all threads have their local copy of a local variable. As it is
the code is not synchronized at all.
- What is the output of the following code ?
try {
System.out.println("Test !");
}
catch(InterruptedException ee) {
System.out.println("The main thread was interrupted !");
}
\/\/\/\/\/\/\/\/\/\/
The code does not compile because the exception InterruptedException is never thrown. (InterruptedException is checked)
- What is the output of the following code ?
try {
System.out.println("Test !");
}
catch(IndexOutOfBoundsException ee) {
System.out.println("The main thread was interrupted !");
}
\/\/\/\/\/\/\/\/\/\/
Test !
Attention: IndexOutOfBoundsException is not checked (for this reason the code compiles)
- Can you attach many threads to a class extending Thread ? True/False.
\/\/\/\/\/\/\/\/\/\/
Answer: True.
This is a tricky question. Bear in mind that the class Thread implements the Runnable interface. As a result
you could always write something like this:
class MyThread extends Thread{}
MyThread th = new MyThread();
new Thread(th).start();
new Thread(th).start();
new Thread(th).start();
Thus to the object "th" you can attach many threads.
OTOH it is true that you cannot call many times the start() method on the same object:
th.start();
th.start();
because the code will fail at runtime.
- Can you attach many threads to a class implementing Runnable ? True/False.
\/\/\/\/\/\/\/\/\/\/
Answer: True
- Will the following code compile ? Yes/No
class CDummy
{
int someInt;
void printData(String input) {
synchronized (someInt) {
System.out.println(input);
}
}
}
\/\/\/\/\/\/\/\/\/\/
No ! Synchronization can only be done on Object(s) not primitives.
- When an IllegalMonitorStateException is thrown ?
\/\/\/\/\/\/\/\/\/\/
When the wait() or notify() functions are called on an Object on
which the current thread does not have a lock.
- Does the following code compile ? Yes/No
public class CDummy
{
static int someVar1 = 9;
int someVar2 = 11;
public static void main(String args[])
{
System.out.println("CDummy.");
NestedTwo ns2 = new CDummy().new NestedTwo();
System.out.println(ns2.getOuterVariable2());
}
class NestedTwo
{
static int getOuterVariable1() {return someVar1;}
int getOuterVariable2() {return someVar2;}
}
}
\/\/\/\/\/\/\/\/\/\/
No. Inner classes cannot have static attributes or members. The
function getOuterVariable1() is static.
- What are nested classes ?
\/\/\/\/\/\/\/\/\/\/
Any class defined inside another class.
- What are inner classes ?
\/\/\/\/\/\/\/\/\/\/
Non-static nested classes.
- How many types of nested classes there are ?
\/\/\/\/\/\/\/\/\/\/
Static nested classes and inner classes.
- How can you define a static inner class ?
\/\/\/\/\/\/\/\/\/\/
Inner classes are not static by definition, nor do they allow any
static member functions or attributes.
