Description:
Suppose you are given the following code:
class ZeroEvenOdd {
public ZeroEvenOdd(int n) { … } // constructor
public void zero(printNumber) { … } // only output 0’s
public void even(printNumber) { … } // only output even numbers
public void odd(printNumber) { … } // only output odd numbers
}
The same instance of ZeroEvenOdd will be passed to three different threads:
Thread A will call zero() which should only output 0’s.
Thread B will call even() which should only ouput even numbers.
Thread C will call odd() which should only output odd numbers.
Each of the threads is given a printNumber method to output an integer. Modify the given program to output the series 010203040506… where the length of the series must be 2n.
Example 1:
Input: n = 2
Output: “0102”
Explanation: There are three threads being fired asynchronously. One of them calls zero(), the other calls even(), and the last one calls odd(). “0102” is the correct output.
Solution:
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class ZeroEvenOdd {
private int n;
private volatile boolean iszero = true;
private volatile boolean isodd = true;
private volatile boolean iseven = false;
private Object lock = new Object();
public ZeroEvenOdd(int n) {
this.n = n;
}
public void zero(IntConsumer printNumber) throws InterruptedException {
for(int i = 0; i < n; i++) {
synchronized (lock) {
while(!iszero)
lock.wait();
printNumber.accept(0);
iszero = false;
lock.notifyAll();
}
}
}
public void even(IntConsumer printNumber) throws InterruptedException {
for(int i = 2; i <= n; i += 2){
synchronized(lock){
while(iszero || !iseven)
lock.wait();
printNumber.accept(i);
iseven = false;
iszero = true;
isodd = true;
lock.notifyAll();
}
}
}
public void odd(IntConsumer printNumber) throws InterruptedException {
for(int i = 1; i <= n; i += 2) {
synchronized(lock) {
while(iszero || !isodd)
lock.wait();
printNumber.accept(i);
iseven = true;
isodd = false;
iszero = true;
lock.notifyAll();
}
}
}
}