improve CoroutineThreadContextElementDemo

src/test/java/com/alibaba/demo/coroutine/CoroutineThreadContextElementDemo.kt

@@ -9,12 +9,24 @@ fun main() = runBlocking {
     threadLocal.set("main")
     println("Pre-main, current thread: ${Thread.currentThread()}, thread local value: ${threadLocal.get()}")
 
-    val job = launch(Dispatchers.Default + threadLocal.asContextElement(value = "launch")) {
+    val block: suspend CoroutineScope.() -> Unit = {
         println("Launch start, current thread: ${Thread.currentThread()}, thread local value: ${threadLocal.get()}")
         yield()
         println("After yield, current thread: ${Thread.currentThread()}, thread local value: ${threadLocal.get()}")
     }
-    job.join()
 
+    println()
+    launch(block = block).join()
+
+    println()
+    launch(threadLocal.asContextElement(value = "launch"), block = block).join()
+
+    println()
+    launch(Dispatchers.Default, block = block).join()
+
+    println()
+    launch(Dispatchers.Default + threadLocal.asContextElement(value = "launch"), block = block).join()
+
+    println()
     println("Post-main, current thread: ${Thread.currentThread()}, thread local value: ${threadLocal.get()}")
 }