I need to write a java program that creates a thread to print integers 1 - 3 inclusive. When 2 is printed, the thread waits until a second thread has finished before printing 3. The second thread prints the letter z three times.
possible outputs include: 1z2zz3 z1z2z3 12zzz3
How can I wait for a thread to finish?
Here is a solution for your task. With synchronized and wait you can solve this.
public static void main(String[] args) {
new PrintingTheads().doJob();
}
}
class PrintingTheads{
private Object objsynch= new Object();
private int numberofZ = 0;
public void doJob(){
new Thread(){
public void run(){
while(true){
System.out.print(1); Thread.yield(); // thread yeald is here for better "mixing the number 1,2 and Z letters"
System.out.print(2);Thread.yield();
synchronized (objsynch) {
while(numberofZ!=3) try{objsynch.wait(10);} catch(InterruptedException e){}
}
System.out.println(3);
try{Thread.sleep(1000);} catch(InterruptedException e){} // * this part is only for easy to see what happened and can be deleted
synchronized (objsynch) {
numberofZ = 0;
objsynch.notifyAll();
}
}
}
}.start();
new Thread(){
public void run(){
while(true){
synchronized (objsynch) {
while(numberofZ!=0) try{objsynch.wait(10);} catch(InterruptedException e){}
}
for(int i= 0;i<3;i++) {System.out.print('z');Thread.yield();}
synchronized (objsynch) {
numberofZ=3;
objsynch.notifyAll();
}
}
}
}.start();
}
}
You can call the join method on a Thread object to wait for it to finish. Example:
public class JoinTest implements Runnable {
public static void main(String[] args) throws Exception {
System.out.println("in main");
Thread secondThread = new Thread(new JoinTest());
secondThread.start();
secondThread.join();
System.out.println("join returned");
}
@Override
public void run() {
System.out.println("second thread started");
// wait a few seconds for demonstration purposes
try {
Thread.sleep(3000);
} catch(InterruptedException e) {}
System.out.println("second thread exiting");
}
}
Note: it doesn't matter whether you choose to extend Thread or implement Runnable for this - any Thread object can be joined.
The output should be:
in main
second thread started
and then 3 seconds later:
second thread exiting
join returned
You need some kind of synchronisation mechanism. Commonly a semaphore or mutex.
Eg.
Semaphore mutex = new java.util.concurrent.Semaphore(1); // 1 - means single resource
In counting thread
{
for (int i = 1; i < 3; i++) {
System.print("i");
if (i == 2) {
// wait for other thread to finish
mutex.acquire();
}
}
System.println(); // Output newline at end.
}
in 'zzz' thread
{
// This should be done before the other thread starts
// and will make it wait when it wants to acquire the mutex.
mutex.acquire();
for (int i = 1; i < 3; i++) {
System.print("z");
}
// Allow the other thread to acquire the mutex.
mutex.release();
}
Please excuse if my syntax is not 100% java, and no exception handling.
check this
public class Test {
private static int number=1;
private static int z=1;
private static Thread t2;
public static void main(String[] args) {
Thread t = new Thread(new Runnable() {
public void run() {
for (int i = 0; i <= 20; i++) {
if (number == 3){
while (z<4);
}
System.out.print(number++);
if (number == 4){
number = 1;
z=1;
}
}
t2.stop();
}
});
t2 = new Thread(new Runnable() {
public void run() {
while(true){
while(z<=3){
System.out.print("z");
z++;
}
System.out.print("");
}
}
});
t.start();
t2.start();
}
}
You can use CountDownLatch for that purposes, as example:
import java.util.concurrent.CountDownLatch;
public class Test {
public static void main(String... s){
final CountDownLatch cdl = new CountDownLatch(1);
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
System.out.println(1);
System.out.println(2);
try {
cdl.await();//wait another thread finish
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(3);
}
});
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
for(int i=0;i<3;i++)
System.out.println("z");
cdl.countDown();//notify all waiting threads
}
});
t2.start();
t1.start();
}
}
outputs: 1zzz23 , z12zz3 ...
I think You want to wait a thread.So you can Put this line inside your run() method.
Thread.sleep(1000);
So every thread will held for 1 sec while completing execution.Hope this will work.Try it and let me know.
