怎样建设影视网站,什么网站容易做,外贸网站代运营,广州住房建设部网站1、接口方法声明异常与实现类方法声明异常的关系 2、异常链——示例 3、try-catch-finally 推荐组织结构#xff0c;及其缺陷 4、断言
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1、接口方法声明异常与实现类方法…1、接口方法声明异常与实现类方法声明异常的关系 2、异常链——示例 3、try-catch-finally 推荐组织结构及其缺陷 4、断言
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1、接口方法声明异常与实现类方法声明异常的关系
接口方法声明异常实现类的方法可以忽略异常声明
接口方法没有声明异常实现类的方法不能添加异常声明 interface IRefactorTest{/*** 假设原方法为public void test1();* 如果重构添加方法public void test1() throws Exception;* 两个方法签名相同无法通过编译器* * 如果重构改变public void test1();* 为public void test1() throws Exception;* 那么以前实现的方法就没有抛出异常(如下test1())*///public void test1();public void test1() throws Exception;public double getNum() throws Exception;
}public class InterfaceWithThrowRefactor implements IRefactorTest{/*** For this reason I prefer to define a superclass exception for a whole package * (such as SQLException for java.sql) and ensure that public methods only declare* this exception in their throws clause. That way I can define subclass exceptions * if I want to, but this wont affect a caller who knows only about the general case.*/Overridepublic double getNum(){return 555.55;}/*** 如果接口的方法有声明异常实现类的方法可以忽略该异常如下* 如果接口的方法没有声明异常则实现类的方法不能有声明的异常*/Overridepublic void test1(){System.out.println(Just test...);}public static void main(String[] args) {InterfaceWithThrowRefactor iwtr new InterfaceWithThrowRefactor();iwtr.test1();try {double d iwtr.getNum();System.out.println(d d);} catch (Exception e) {e.printStackTrace();}}
}
2、异常链——示例 /*** Exception for subsystem*/
class SubsystemException extends Exception{private static final long serialVersionUID -1395025218830523517L;public SubsystemException() {super();}public SubsystemException(String message) {super(message);}
}public class ExceptionThrowChain {public static void main(String[] args) {try {normalChain();} catch (SubsystemException e) {e.printStackTrace();}try {goodChain();} catch (SubsystemException e) {e.printStackTrace();}}private static void normalChain() throws SubsystemException{try {throwException();} catch (SQLException e) {throw new SubsystemException(database error: e.getMessage());}}private static void goodChain() throws SubsystemException{try {throwException();} catch (SQLException e) {SubsystemException sube new SubsystemException(database error);sube.initCause(e);throw sube;}}//Method mock throw exceptionprivate static void throwException() throws SQLException{throw new SQLException(Cant connect to database!);}
}normalChain( ) 方法不能跟踪——示例 goodChain( ) 方法能跟踪——示例
3、try-catch-finally 推荐组织结构及其缺陷 实际代码示例 // Read a file as a single string:public static String read(String fileName) {StringBuilder sb new StringBuilder();try {BufferedReader in new BufferedReader( new FileReader(new File(fileName)) );try {String s;while ((s in.readLine()) ! null) {sb.append(s);sb.append(\n);}} finally {in.close();}} catch (IOException e) {throw new RuntimeException(e);}return sb.toString();}
分析
a、如果 BufferedReader in ...; 抛出异常如文件不存在因为没有进入内部 try因而不会执行内部 finally 的 in.close( ); 语句。
b、如果 BufferedReader in ....; 成功构造在内部 try 语句中抛出异常则会执行内部 finally 对应的 in.close(); 语句。
c、将检查的异常 IOException 转换为运行时异常 RuntimeException方法就不必声明抛出异常了这种构造是可跟踪的。
缺陷当内部 try 和 finally 都抛出异常时finally 的异常会覆盖 try 的异常导致 try 内的异常丢失 异常丢失示例模拟 public class TextFile{//Test exception in finally override other exceptionpublic static String read(InputStream in, int size) {StringBuilder sb new StringBuilder();try {try {if( size0 ){System.out.println(throw SubsystemException.);throw new SubsystemException(Exception that i want.);}} finally {in.close();}} catch (IOException e) {throw new RuntimeException(e);} catch (SubsystemException e) {throw new RuntimeException(e);}return sb.toString();}
} 模拟当传入参数 size 为 0 时抛出SubSystemExceptionpublic class TextFileTest {Testpublic void testRead(){//NewInputStream easyIn EasyMock.createMock(InputStream.class);//Call-recordtry {easyIn.close();EasyMock.expectLastCall().andThrow( new IOException(IOException of easy mock!));} catch (IOException e) {}//ReplayEasyMock.replay( easyIn );TextFile.read(easyIn, 0);//VerifyEasyMock.verify(easyIn);}
}
模拟模拟 InputStream 对象使其调用 close( ) 方法时抛出 IOException
注意EasyMock 模拟的是类而非接口那么就必须都用模拟类的 EasyMock 来调用 expectLastCall() reaplay() verify() 等方法 运行报错如下 而且有如下输出 由上面两图可得出结论finally 内的 IOException 覆盖了内部 try 的 SubsystemException
4、断言
公有的方法即API用异常非公有方法通常使用断言来检查参数。
When should you choose assertions? Keep these points in mind: 1、Assertion failures are intended to be fatal, unrecoverable errors. 2、Assertion checks are turned on only during development and testing.
示例 public class TestAssert {public void testAssert(){int[] a new int[]{1, 22 , 3 ,5};//length is 3//offset is 2//a.length is 4//length a.length - offset, Error!sort( a, 2, 3 );}private void sort( int a[], int offset, int length ){assert a ! null;assert offset 0 offset a.length;assert length 0 length a.length - offset;System.out.println(Just a test!);}
}测试代码 public class TestAssertTest {Testpublic void testTestAssert() {TestAssert ta new TestAssert();ta.testAssert();}
}Eclipse启动运行时断言 测试结果报错
