public class FinallyWorks {static int count=0;public static void main(String[] args) {while(true) {try {if(count++==0) {throw new Exception();}System.out.println("No Exception");}catch(Exception e) {System.out.println("Exception");}finally {System.out.println("In finally");if(count==3) break;}}}
}

这个程序也给了我们一些思路，当Java中的异 常不允许我们回到异常抛出的地点时，那么该如何应对呢?如果把try块放在循环里，就建立了一个“程序继续执行之前必须要达到”的条件。还可以加入一个static类型的计数器或者别的装置，使循环在放弃以前能尝试-定的次数。这将使程序的健壮性更上一个台阶。

当要把除内存之外的资源恢复到它们的初始状态时，就要用到finally子句。这种需要清理的资源包括:已经打开的文件或网络连接,在屏幕上画的图形，甚至可以是外部世界的某个开关,而且在异常没有被当前处理程序捕获的情况下，异常处理机制也会也会跳到更高一层的异常处理程序之前，执行finally子句。最后当涉及break和continue语句的时候，finally 子句也会得到执行。请注意，如果把finally子句和带标签的break及continue配合使用，在Java里就没必要使用goto语句了。

public class InputFile {private BufferedReader in;public InputFile(String fname) throws Exception {try {in = new BufferedReader(new FileReader(fname));} catch (FileNotFoundException e) {System.out.println("can not open" + fname);throw e;} catch (Exception e) {try {in.close();} catch (IOException e2) {System.out.println("in.close unseccessful");}throw e;} finally {}}public String getLine() {String s;try {s = in.readLine();} catch (IOException e) {throw new RuntimeException("readLine failed");}return s;}public void dispose() {try {in.close();System.out.println("dispose successful");} catch (IOException e2) {throw new RuntimeException("in.close failed");}}public static void main(String[] args) throws Exception {InputFile p=new InputFile("FinallyWorks.java");}
}

如果FileReader的构造器失败了，将拋出FileNotFoundException异常。 对于这个异常，并不需要关闭文件，因为这个文件还没有被打开。而任何其他捕获异常的catch子句必须关闭文件，因为在它们捕获到异常之时，文件已经打开了(当然，如果还有其他方法能抛出FileNotFoundException,这个方法就显得有些投机取巧了。这时，通常必须把这些方法分别放到各自的try块里)。close0方法也可能会抛出异常，所以尽管它已经在另一个Catch子句块里了，

public class Cleanup {public static void main(String[]  args) {try {InputFile  in =new InputFile("Cleanup.java");try {String s;int i=1;while((s=in.getLine())!=null) {;}}catch(Exception e) {System.out.println("Caught Exception in main");e.printStackTrace(System.out);}finally {in.dispose();}}catch(Exception e) {System.out.println("InputFile construction failed");}}
}

class NeedsCleanup {private static long counter = 1;private final long id = counter++;public void dispose() {System.out.println("NeedsCleanup " + id + " dispose");}
}class ConstructionsException extends Exception {
}class NeedsCleanup2 extends NeedsCleanup {public NeedsCleanup2() throws ConstructionsException {}
}public class CleanupIdiom {public static void main(String[] args) {NeedsCleanup nc1=new NeedsCleanup();try {}finally {nc1.dispose();}NeedsCleanup nc2=new NeedsCleanup();NeedsCleanup nc3=new NeedsCleanup();try {}finally {nc2.dispose();nc3.dispose();}try {NeedsCleanup2 nc4=new NeedsCleanup2();try {NeedsCleanup2 nc5=new NeedsCleanup2();try {}finally {nc5.dispose();}}catch(ConstructionsException e) {System.out.println(e);}finally {nc4.dispose();}}catch(ConstructionsException e) {System.out.println(e);}}
}

class A extends Exception{}
class B extends A{}
//异常匹配
public class Human {public static void main(String[] args) {try {throw new B();}catch(B s) {System.out.println("caught B");}catch(A a) {System.out.println("caught A");}//匹配基类try {throw new B();}catch(A a) {System.out.println("caught A");}}
}

try {throw new B();}catch(A s) {System.out.println("caught B");}catch(B a) {System.out.println("caught A");}