Exercise $1$:

public class TwoThread extends Thread $\{$

public void run$()\{$

for $($ int i $=0$; i $<20$; i$++)\{$

System.out.println$($Thread$.$currentThread $().$getName$())$;

$\}$

$\}$

public static void main$($String$[]$ args$)\{$

TwoThread T$1=$ new TwoThread$()$;

T$1.$start$()$;

for $($ int i $=0$; i $<20$; i$++)\{$

System.out.println$("$Main thread"$)$;

$\}$

$\}\}$

$1.$ What is it doing this program

$2.$ Compile and execute the program

Note: starting a thread is done via the start $()$ method. The main $()$ method is itself in a thread $($the main thread$)$

$3.$ Modify the previous program so that: create $2$ others threads T$2$ and T$3$ using the class

Thread and TwoThread. Execute the program and explain what you see $?$

$4.$ Modify the previous program so that the thread T$2$ complete its execution by blocking

all others thread after that they can run.

Note: you can use join$()$ method. The join$()$ method is used to hold the execution of currently running thread

until the specified thread is dead$($finished execution$).$

Exercise $2$: Write in java a program that uses two threads in parallel: $-$

the first will display the $26$ letters of the alphabet; $--$

the second will display numbers from $1$ to $26.$

the second thread must wait $200$ ms after it e