Java 异常: try...catch...finally

在看下面的内容之前，想问大家一个问题：

finally 语句是不是一定会被执行 

使用 Integer.valueOf 方法模拟异常，来说明关于 try catch finally 之间的问题。

示例 1：没有异常，正常情况

public class TryCatchFinally {public static void main(String[] args) {try {System.out.println("try statement     :-)");Integer.valueOf("2");} catch (NumberFormatException nfe) {System.out.println("catch statement   :-)");} finally {System.out.println("finally statement :-)");}}}

示例 2：没有异常，正常情况，但是 try 语句里面添加 return 

public class TryCatchFinally {public static void main(String[] args) {try {System.out.println("try statement     :-)");Integer.valueOf("2");return;} catch (NumberFormatException nfe) {System.out.println("catch statement   :-)");} finally {System.out.println("finally statement :-)");}}}

示例 1 和 示例 2 的运行结果一致：

示例 3：制造异常

public class TryCatchFinally {public static void main(String[] args) {try {System.out.println("try statement     :-)");Integer.valueOf("bluetooth");} catch (NumberFormatException nfe) {System.out.println("catch statement   :-)");} finally {System.out.println("finally statement :-)");}}}

示例 4：制造异常，catch 语句里面添加 return

public class TryCatchFinally {public static void main(String[] args) {try {System.out.println("try statement     :-)");Integer.valueOf("bluetooth");} catch (NumberFormatException nfe) {System.out.println("catch statement   :-)");return;} finally {System.out.println("finally statement :-)");}}}

示例 3 和 示例 4 的运行结果一致：

由此，可以看出以上四种情况，finally 语句都被执行了。

示例 5：制造异常，catch 语句里面添加 return

目的：验证finally代码块后面的代码是否会被执行 ？？？？？？

public class TryCatchFinally {public static void main(String[] args) {try {System.out.println("try statement     :-)");Integer.valueOf("bluetooth");} catch (NumberFormatException nfe) {System.out.println("catch statement   :-)");return;} finally {System.out.println("finally statement :-)");}System.out.println("out of try...catch...finally statement");}}

执行结果：

如果将 catch 语句里面添加 return 注释掉，执行结果：

示例 6：制造异常，try 语句里面添加 return 

public class TryCatchFinally {public static void main(String[] args) {try {System.out.println("try statement     :-)");Integer.valueOf("dd");return;} catch (NumberFormatException nfe) {System.out.println("catch statement   :-)");} finally {System.out.println("finally statement :-)");}System.out.println("out of try...catch...finally statement");}}

执行结果：

示例 7：无异常，try 语句里面添加 return 

public class TryCatchFinally {public static void main(String[] args) {try {System.out.println("try statement     :-)");Integer.valueOf("2");return;} catch (NumberFormatException nfe) {System.out.println("catch statement   :-)");} finally {System.out.println("finally statement :-)");}System.out.println("out of try...catch...finally statement");}}

执行结果（无异常，return 返回，所以finally代码块后面的语句就不会执行：-）

以上种种迹象表明：

finally 语句都被执行了，但是还有另外一种情况没有被验证，接着往下看 

就是在 try...catch... 里面退出 JVM ：

public class TryCatchFinally {public static void main(String[] args) {try {System.out.println("try statement     :-)");Integer.valueOf("2eer");System.exit(0);} catch (NumberFormatException nfe) {System.out.println("catch statement   :-)");System.exit(0);} finally {System.out.println("finally statement :-)");}System.out.println("out of try...catch...finally statement");}}

执行结果：

try 或者 catch 语句里面（任意一个）调用 System.exit ，那么 finally 语句就不会被执行。

see also：http://stackoverflow.com/questions/18097496/java-exception-not-caught