Mea Cook

Thank you Bert! I am only few days on ranch, but I like it very much.

I'll do my best and next time write the full questions not only code.

This question is resolved for me and I close it

Really speaking I don't understand te role of synchronized in this context. Can anybordy help?

private synchronized void message(int i) { ... }

this is the same as

private void message(int i) { synchronized(this) ... }

What object will be locked: from class Thread or Messager? And how long?
I thought, that if 1 Thread is locked, then runs to the end the 2 Thread and then the 1 Thread runs to the end.
But the answer shows, it is not correct...

Thank you

Hello all,

I have some problems with SELF TEST, exercise 1 (K&B, Java 1.5, Chapter 9, page 733)

According to the book the answer is Wallace-1 Gromit-1 Gromit-2 Wallace-2

I compiled the code and got another result. Wallace-1 Wallace-2 Gromit-1 Gromit-2

public class Messager implements Runnable{ private String name; public void run(){ message(1); message(2); } public Messager(String param1){ this.name = param1; } private synchronized void message(int param1) { System.out.println(name + "-" + param1 + " "); } public static void main(String [] args) { new Thread(new Messager("Wallace")).start(); new Thread(new Messager("Gromit")).start(); } }


Thank you all in advance

Thank you all!!!

Thank you! It works!!!

I have quation about:

why setChar(0, 'A' + 1) doesn't work and

why 3 steps with a temporal variable c are need:

char c;
c = s.charAt(0);
c++;
s.setChar(0, c);

Must I open a new topic?

Best regards

Ankit, I changed the code. Now I get output. But only A's...

class MyThread extends Thread{ StringBuffer s; char c; public MyThread(){ super(); } public MyThread(StringBuffer aPrm1){ s = aPrm1; } public void run(){ synchronized(s){ for (int i = 0; i < 100 ; i++){ System.out.print(s); } } c = s.charAt(0); c = c++; s.setCharAt(0, c); } } public class Test04 { public static void main(String [] args) { StringBuffer localString = new StringBuffer("A"); MyThread t1 = new MyThread(localString); [b]MyThread t2 = new MyThread(localString); MyThread t3 = new MyThread(localString);[/b] t1.start(); t1.setName("1.Thread"); t2.start(); t2.setName("2.Thread"); t3.start(); t3.setName("3.Thread"); } }

I edited it.

Now I have anothe Problem: NullPointerException. Ist here a problem with synchronisation?

class MyThread extends Thread{ StringBuffer s; char c; public MyThread(){ super(); } public MyThread(StringBuffer aPrm1){ s = aPrm1; } public void run(){ synchronized(s){ for (int i = 0; i < 100 ; i++){ System.out.print(s); } c = s.charAt(0); c = c++; s.setCharAt(0, c); } } } public class Test04 { public static void main(String [] args) { StringBuffer localString = new StringBuffer("A"); MyThread t1 = new MyThread(localString); MyThread t2 = new MyThread(); MyThread t3 = new MyThread(); t1.start(); t1.setName("1.Thread"); t2.start(); t2.setName("2.Thread"); t3.start(); t3.setName("3.Thread"); } }

May be it is easy, but I don't know how to increment from A to B... and so on using charAt
Yes, I know the type of the return value. But it isn't my problem.

class MyThread extends Thread{ StringBuffer s; public MyThread(){ super(); } public MyThread(StringBuffer aPrm1){ s = aPrm1; } public void run(){ synchronized(s){ for (int i = 0; i < 2 ; i++){ System.out.print(s); } [b] //s.setCharAt(0, (s.charAt(0)...; [/b] } } } public class Test04 { public static void main(String [] args) { StringBuffer localString = new StringBuffer("A"); MyThread t1 = new MyThread(localString); MyThread t2 = new MyThread(); MyThread t3 = new MyThread(); t1.start(); t1.setName("1.Thread"); t2.start(); t2.setName("2.Thread"); t3.start(); t3.setName("3.Thread"); } }

And how can I increment a letter please??? s.charAt(0) + 1??? It doesn't work
Sorry but I am still not on the road

Thank you,

but I am still by this exercise...

I use in void run() for loop (0 to 99) and print 100 As, how can I use charAt(pos). I thought, I have at the beginning only 1 A in a StringBuffer-Object...And the value of StringBuffer doesnt change during 100 iterations...
And after 100 iterations I must skip to B. Must I do another loop do... while? And how can I skip? if (s.charAt(0) eq 'A')??? But this is not OK if I whant to skip from 'B' to 'C'


Thank you in advance

Hello all,

I have some problems with te exercise 9-2, Chapter 9, p. 710-711

The result must be 100 As, 100 Bs, 100 Cs

In the book are follows steps described:
1. create a class and extend the Tread class (OK, no problem)
2. override te run of Thread. This is were te synch block will go (OK)
3. create a constructor tat accept StringBuffer (OK)
4 lock StringBuffer object (OK)
5 within block output StringBuffer 100 times and then increment te letter in the StringBuffer???
6. in main() create StringBuffer object using letter A, create 3 instances and start 3 of them (OK)

Thank you very much