Exception in thread "main" java.lang.NullPointerException at com.imooc.collection.SetTest.testSetContains(SetTest.java:129) public void testSetContains(){ System.out.println("備選課程中是否包含課程： " + course2.name + "," + student.courses.contains(course2));//這個語句越界了。。 } 球解釋為什么越界了。代碼都一樣