Threads-synchronized blocks,Valentine &Michael and Others,Help needed

[suresh seeram]

Dear Friends,
1. I have one doubt..
at comment //1.Double inthe following code , If I replace InterruptedException with Exception.. I got error..Like found:Exception, required: Throwable.. why this is happening..
InterruptedException is subclass of Excpetion.
2. I am not able to understand clearly how does the synchronized blocks works.. Can you explain the following code and with different situations.. So it will clear to me.. please help me because i am writing JCP in two days..

class Reetrant{
String s=new String();
public void a(){
System.out.println(Thread.currentThread().getName());
     synchronized(this){
     try{
     Thread.sleep(1000);
     }catch(InterruptedException e){ //1.Doubt
     }
b();
System.out.println("In a");
synchronized(s){
System.out.println("In syn block");
}
  }
}
public  void b(){
synchronized(s){
System.out.println("in b");
}
}
}
class Synchr1 implements Runnable{
static Reetrant r1=new Reetrant();
public static void main(String args[]){
  Synchr1 s1=new Synchr1();
  //Synchr1 s2=new Synchr1();
  Thread t1=new Thread(s1,"FirstThred");
  Thread t2=new Thread(s1,"SecondThread");
  t1.start();
  t2.start();
}
public void run(){

r1.a();
}
}

3. Explain the following code..
 class thread implements Runnable{
StringBuffer s1=new StringBuffer("Suresh");
StringBuffer s2=new StringBuffer("babu");
public void run(){
new Thread(){
public void run()
{
System.out.println("In first run");
synchronized (s1)
{
s1.append("s");
synchronized(s2)
   {
s2.append("a");
}
System.out.println(s1);
System.out.println(s2);
}
 } 
  }.start();

new Thread(){
public void run()
{
System.out.println("In second run");
 synchronized (s1)
{
  s1.append("M");
synchronized(s2)
{
s2.append("N");
}
System.out.println(s1);
System.out.println(s2);
}
}
}.start();
}

 public static void main(String args[]){
 Thread t=new Thread(new thread(),"Impthread");
 t.start();
 }

}

thanks in advance,
Suresh
[This message has been edited by suresh seeram (edited October 19, 2001).]
[This message has been edited by Marilyn deQueiroz (edited October 19, 2001).]

[Marilyn de Queiroz]

If I replace InterruptedException with Exception.. I got error..Like found:Exception, required: Throwable.. why this is happening..
InterruptedException is subclass of Excpetion.

<pre>
class Reetrant{
String s=new String();
public void a(){
System.out.println(Thread.currentThread().getName());
synchronized(this){
try{
Thread.sleep(1000);
}catch(InterruptedException e){ //1.Doubt
}
< snipped >
}
</pre>

Maybe you spelled Exception wrong. I'm not getting any error when I substitute Exception for IOException

[This message has been edited by Marilyn deQueiroz (edited October 19, 2001).]

[suresh seeram]

Dear Marilyn deQueiroz ,
thanks for your response.. Still I am getting error..There may be error in my editor or something..
I think this is not important for JCP exams..
Could you please explain codes 2 and 3..

thanks in advance..
regards,
Suresh

[R K Singh]

I also tried with Exception and did not get any error.
Now for first prog:
<pre>
class Reetrant{
String s=new String();
//String thrdName ;
public void a(){
String thrdName;
thrdName = Thread.currentThread().getName();
//synchronized(thrdName){
System.out.println(thrdName);
synchronized(this){
try{
System.out.println(thrdName + ": B4 sleep()");
Thread.sleep(1000);
//wait(100);
// Thread.yield();
}catch(Exception e){
//1.Doubt
}
b(thrdName);
//b();
System.out.println(thrdName + ": In a");
synchronized(s){
System.out.println(thrdName + ": In syn block");
}
Thread.yield();
}// end synch block
//}
synchronized(this){
try{
System.out.println(thrdName + ": B4 sleep() after first sync and in second sync");
Thread.sleep(1000);
//wait(100);
}catch(Exception e){
//1.Doubt
}
}
System.out.println(thrdName + ": end of a()");
}// end if method a()
public void b(String thrdName){
//public void b(){
System.out.println(thrdName + ": in b WT sync");
//synchronized(thrdName ){
synchronized(s){
System.out.println(thrdName + ": in b");
}
//}
}
} // end of Reetrant
class Synchr1 implements Runnable{
Reetrant r1 = new Reetrant();
public static void main(String args[]){
Synchr1 s1=new Synchr1();
//Synchr1 s2=new Synchr1();
Thread t1=new Thread(s1,"FirstThred");
Thread t2=new Thread(s1,"SecondThread");
//Thread t2=new Thread(s2,"SecondThread");

t1.start();
t2.start();
}

public void run(){
r1.a();
}
}

</pre>

you can remove comments and then put comments on yield() and/or wait() and/or sleep() to see what happens...
Now when you synchronize an object for a block then same object can not run the same block of statement.
sleep() does leave the lock so even a thread is sleeping it does not realease the lock.
but if you try wait(long time) or yield() you can find that other thread starts executing.
condition is that object should be same.
if you have s2 object reference then there will be no problem as there will be two different objects.

for ur second program:
there are three (if u include main thread also then 4)threads are running. one which start in main(), other two are starts by the thread u created. They are created by using annonymous class.
code is like
<pre>
new Thread() // no name for the class
{ public void run() { // overriding method run() for annonymous class
// some code
}.start() // register with the thread schedular( call the run() )
</pre>
correct me if wrong.

[This message has been edited by ravish kumar (edited October 19, 2001).]