// lowlevel/SyncOnObject.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Synchronizing on another object

import onjava.Nap;

import java.util.Arrays;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.stream.Collectors;

class DualSynch {
    ConcurrentLinkedQueue<String> trace =
            new ConcurrentLinkedQueue<>();
    private Object syncObject = new Object();

    public synchronized void f(boolean nap) {
        for (int i = 0; i < 5; i++) {
            trace.add(String.format("f() " + i));
            if (nap) new Nap(0.01);
        }
    }

    public void g(boolean nap) {
        synchronized (syncObject) {
            for (int i = 0; i < 5; i++) {
                trace.add(String.format("g() " + i));
                if (nap) new Nap(0.01);
            }
        }
    }
}

public class SyncOnObject {
    static void test(boolean fNap, boolean gNap) {
        DualSynch ds = new DualSynch();
        List<CompletableFuture<Void>> cfs =
                Arrays.stream(new Runnable[]{
                                () -> ds.f(fNap), () -> ds.g(gNap)})
                        .map(CompletableFuture::runAsync)
                        .collect(Collectors.toList());
        cfs.forEach(CompletableFuture::join);
        ds.trace.forEach(System.out::println);
    }

    public static void main(String[] args) {
        test(true, false);
        System.out.println("****");
        test(false, true);
    }
}
/* Output:
f() 0
g() 0
g() 1
g() 2
g() 3
g() 4
f() 1
f() 2
f() 3
f() 4
****
f() 0
g() 0
f() 1
f() 2
f() 3
f() 4
g() 1
g() 2
g() 3
g() 4
*/