Question on char & Thread in Marcus's mock

[Orion alpha]

in Marcus Green Mock Exam 3, Question 3:
int i=2+'2';
it said the above is valid, so i tried the following code for testing.
line 1:int i3 = 1+'1';
line 2: System.out.println("int3 is " + i3);//give 50; since ASCII of char '1' is 49, 49+1 =50
line 3:
line 4: char z = 1;
line 5: System.out.println("char is "+z);// give some symbol that i don't understand, why?
line 6:
line 7: int i4 = 1+z;
line 8: System.out.println("int plus char is "+i4); //give 2 which is expected value, but what is the difference between this and line 1 and line7?
in Marcus Green Mock Exam 2, Question 42:
It said that "A thread can obtain a mutually exclusive lock on a synchronized method of an object" is true.
Why?
Besides, "Java uses a pre-emptive, co-operative system for determining which Thread will execute" - is this statement correct?

[Thomas Kijftenbelt]

Hi,
line 1: int i3 = 1+'1';
line 2: System.out.println("int3 is " + i3);//give 50; since ASCII of char '1' is 49, 49+1 =50
line 3:
line 4: char z = 1;
line 5: System.out.println("char is "+z);// give some symbol that i don't understand, why?
line 6:
line 7: int i4 = 1+z;
line 8: System.out.println("int plus char is "+ i4); //give 2 which is expected value, but what is the difference between this and line 1 and line7?
-> line 5: the first ascii characters can't be displayed, they represent all sorts of things (a carriage return / a line feed / a bell / etc.), so they look strange on the display.
-> in line 8: the variable z is converted to int; as you assigned it with the value 1, it is converted to int value 1, and added to int value 1, it gives 2
-> in line 1 you add the int value 1 with the character literal '1', this char. literal is also converted, and gives int value 49, so the addition results in 50 -> that the difference
greetings,
TK

[Thomas Kijftenbelt]

Hi,
regarding your second question:
the thread can obtain a lock on the object, by entering a piece of synchronized code; as soon as this happens, the thread gets a lock on the object, and no other thread can enter the synchronized method of this object.

Besides, "Java uses a pre-emptive, co-operative system for determining which Thread will execute" - is this statement correct?

I would say yes, this is a definition of the thread scheduler.
Greetings,
TK

[Marcus Green]

"Besides, "Java uses a pre-emptive, co-operative system for determining which Thread will execute" - is this statement correct? "

This is not a quote from me, the scheduling algorithm used by Java threads is platform dependent.
Marcus

[Paulo Silveira]

Originally posted by Marcus Green:
"Besides, "Java uses a pre-emptive, co-operative system for determining which Thread will execute" - is this statement correct? "

Hum, this is false.
It was pre emptive in the really beginning, and even so, as Marcus said, it is JVM dependent, so you cannot say that java is pre emptive or time sliced.