Java线程池为什么核心线程数为0依然能执行？

下面这段代码的线程会执行吗？

ExecutorService es = 
new ThreadPoolExecutor(0, 100000, 100000, TimeUnit.HOURS,new linkedBlockingQueue<>());

答案是会。
但是为啥？

通过线程池的 execute 方法可以看到：

接着思考：
有没有进入队列？
先进入队列还是先创建线程？
都调用了队列的什么方法？

看最终代码：

public static void main(String[] args) {

         class MyQueue implements InvocationHandler {
             private BlockingQueue queue = null;
             public MyQueue(BlockingQueue queue){
                 this.queue = queue;
             }
             @Override
             public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                 System.out.println(method.getName() + "::::::::::::::::::::::::::" + Arrays.toString(args));
                 return method.invoke(queue,args);
             }
         }

        linkedBlockingQueue queue = new linkedBlockingQueue();
        BlockingQueue queue2 = (BlockingQueue)Proxy.newProxyInstance(Test.class.getClassLoader(),new Class[]{BlockingQueue.class},new MyQueue(queue));

        ExecutorService es = new ThreadPoolExecutor(1, 1, 100000, TimeUnit.HOURS, queue2, new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {
                System.out.println("--------------------- new Thread ------------------------");
                return new Thread(r);
            }
        });
        es.execute(new Runnable() {
            @Override
            public void run() {
                System.out.println("hello : " + Thread.currentThread().getId());
                try {
                    Thread.sleep( 1 * 100);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public String toString() {
                return "------------ test obj -------------";
            }
        });

        es.execute(new Runnable() {
            @Override
            public void run() {
                System.out.println("hello : " + Thread.currentThread().getId());
                try {
                    Thread.sleep( 1 * 100);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public String toString() {
                return "------------ test obj -------------";
            }
        });
    }

变换ThreadPoolExecutor对象的第一个参数核心线程数：
核心线程数是0：
先走队列后走线程，执行的是队列的offer与poll

核心线程数大于0：
注意实际线程要大于核心线程数！
先走线程在走offer与take

核心线程数大于0：
注意实际线程要小于等于核心线程数！
先走线程，并且只走take

如果切换队列对象呢？

public static void main(String[] args) {

         class MyQueue implements InvocationHandler {
             private BlockingQueue queue = null;
             public MyQueue(BlockingQueue queue){
                 this.queue = queue;
             }
             @Override
             public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                 System.out.println(method.getName() + "::::::::::::::::::::::::::" + Arrays.toString(args) + "t" + Thread.currentThread().getId());
                 return method.invoke(queue,args);
             }
         }

        BlockingQueue queue = new SynchronousQueue();
        BlockingQueue queue2 = (BlockingQueue)Proxy.newProxyInstance(Test.class.getClassLoader(),new Class[]{BlockingQueue.class},new MyQueue(queue));

        ExecutorService es = new ThreadPoolExecutor(1, 5, 2, TimeUnit.HOURS, queue2, new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {
                System.out.println("--------------------- new Thread ------------------------");
                return new Thread(r);
            }
        });
        es.execute(new Runnable() {
            @Override
            public void run() {
                System.out.println("hello : " + Thread.currentThread().getId());
                try {
                    Thread.sleep( 1 * 1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public String toString() {
                return "------------ test obj -------------";
            }
        });

        es.execute(new Runnable() {
            @Override
            public void run() {
                System.out.println("hello : " + Thread.currentThread().getId());
                try {
                    Thread.sleep( 1 * 1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public String toString() {
                return "------------ test obj -------------";
            }
        });
        es.execute(new Runnable() {
            @Override
            public void run() {
                System.out.println("hello : " + Thread.currentThread().getId());
                try {
                    Thread.sleep( 1 * 100);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public String toString() {
                return "------------ test obj -------------";
            }
        });
    }

再次尝试，注意观察线程ID

最终的出来的结论是：
1、当核心线程数为0的时候，会创建一个非核心线程进行执行
2、核心线程数不为0的时候，如果核心线程数在执行，会有一个非核心线程数从队列中取对象执行线程
3、核心线程数执行的是队列的take，非核心线程数执行队列的offer和poll
4、核心线程数不为0且队列为SynchronousQueue时，就成了单线程运行了