java junit4 单元测试问题

待测试的类 public class Calculator 	{ 				public int add(int a , int b) 					{ 							return a + b; 					} 				public int subtract(int a , int b) 					{ 						   return a - b; 					} public int multiply(int a , int b ) 					{ 								return a * b; 					} 				public  int divide(int a , int b ) throws Exception 					{ 						    if (0 == b) 						    	  throw new Exception("除数不能为0"); return a / b; 					} } 用junit4 的测试 测试代码 public class CalculatorTest 	{ 				private  Calculator cal; @BeforeClass 					public  void setUp() 						{ 							cal = new Calculator(); 						} 					@Test(timeout = 80) 					public void testAdd() 						{ 							 		int result = cal.add(3,5); 							 		Assert.assertEquals(8,result); 						} 		          @Test 		          public void testSubtract() 		        	  { 		        		  		int result = cal.subtract(3,1); 		        		  		Assert.assertEquals(2,result); 		        	  } 		          	@Test 		          	public void testMultiply() 		          		{ 		          					int result = cal.multiply(5,9); 		          					Assert.assertEquals(45,result); 		          		} 		          	@Test(expected = Exception.class) 		          	public void testDivide() throws Exception 		          		{ 		          			  cal.divide(1,0); 		          		} 	} 测试错误 原因 Method setUp () should be static 根据提示 假如把测试代码 前三行改成 private static Calculator cal ; @BeforeClass public static void setUp() {       cal = new Calculator(); } 这样后运行程序就没问题了!求高人指点下迷津