The multi-threading synchronization questions always concentrate on a few keywords: wait, notify, notifyAll, synchronized, volatile.
The following question is the hardest, I ever met. The thread t1 should print integer number from 1–52, the thread t2 should print character from A-Z, the question is how to let the final result to be 12A34B56C… by implement Printer class.
(The Printer class is already finished by the way)
public class Main { public static void main(String[] args) { System.out.println("Hello World!"); Printer p = new Printer(); Thread t1 = new NumberPrinter(p); Thread t2 = new LetterPrinter(p); t1.start(); t2.start(); } } public class LetterPrinter extends Thread { private Printer p; public LetterPrinter(Printer p){this.p = p;} public void run(){ for(char c='A'; c<='Z'; c++){ p.print(c); } } } public class NumberPrinter extends Thread { private Printer p; public NumberPrinter(Printer p){this.p = p;} public void run(){ for(int i = 1; i<=52; i++){ p.print(i); } } } public class Printer { private volatile int m = 1; public synchronized void print(int i ) { while(m % 3 == 0) { try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } } System.out.println(i); m++; notifyAll(); } public synchronized void print(char i) { while (m % 3 != 0) { try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } } System.out.println(i); m++; notifyAll(); } }