Exception in thread "main" java.lang.NullPointerException at com.imooc.collection.SetTest.testSetContains(SetTest.java:129) public void testSetContains(){ System.out.println("备选课程中是否包含课程： " + course2.name + "," + student.courses.contains(course2));//这个语句越界了。。 } 球解释为什么越界了。代码都一样