Java异常处理（二）

  Java基本的异常处理机制已经在上一篇的文章中写出，这篇文章主要分析在try{ ... }catch{ ... }代码块中加return语句 

后，对finally代码块的影响及对其调用者的影响。

  下面看这段代码：

public class TestException {      public TestException() {      }        boolean testEx() throws Exception {          boolean ret = true;          try {              ret = testEx1();          } catch (Exception e) {              System.out.println("testEx, catch exception");              ret = false;              throw e;          } finally {              System.out.println("testEx, finally; return value=" + ret);              return ret;          }      }        boolean testEx1() throws Exception {          boolean ret = true;          try {              ret = testEx2();              if (!ret) {                  return false;              }              System.out.println("testEx1, at the end of try");              return ret;          } catch (Exception e) {              System.out.println("testEx1, catch exception");              ret = false;              throw e;          } finally {              System.out.println("testEx1, finally; return value=" + ret);              return ret;          }      }        boolean testEx2() throws Exception {          boolean ret = true;          try {              int b = 12;              int c;              for (int i = 2; i >= -2; i--) {                  c = b / i;                  System.out.println("i=" + i);              }              return true;          } catch (Exception e) {              System.out.println("testEx2, catch exception");              ret = false;              throw e;          } finally {              System.out.println("testEx2, finally; return value=" + ret);              return ret;  //会屏蔽Exception        }      }        public static void main(String[] args) {          TestException testException1 = new TestException();          try {              testException1.testEx();          } catch (Exception e) {              e.printStackTrace();          }      }  }  

其运行结果如下：（和你想象的是否一致呢？）

i=2i=1testEx2, catch exceptiontestEx2, finally; return value=falsetestEx1, finally; return value=falsetestEx, finally; return value=false

  可以用Eclipse进行Step Into进行逐步调试，会有意想不到的效果。

在看看下面这段代码：

public class TestException {      public TestException() {      }        boolean testEx() throws Exception {          boolean ret = true;          try {              ret = testEx1();          } catch (Exception e) {              System.out.println("testEx, catch exception");              ret = false;              throw e;          } finally {              System.out.println("testEx, finally; return value=" + ret);              return ret;          }      }        boolean testEx1() throws Exception {          boolean ret = true;          try {              ret = testEx2();              if (!ret) {                  return false;              }              System.out.println("testEx1, at the end of try");              return ret;          } catch (Exception e) {              System.out.println("testEx1, catch exception");              ret = false;              throw e;          } finally {              System.out.println("testEx1, finally; return value=" + ret);              return ret;          }      }        boolean testEx2() throws Exception {          boolean ret = true;          try {              int b = 12;              int c;              for (int i = 2; i >= -2; i--) {                  c = b / i;                  System.out.println("i=" + i);              }              return true;          } catch (Exception e) {              System.out.println("testEx2, catch exception");              ret = false;              throw e;          } finally {              System.out.println("testEx2, finally; return value=" + ret);             // return ret;  //会屏蔽Exception        }      }        public static void main(String[] args) {          TestException testException1 = new TestException();          try {              testException1.testEx();          } catch (Exception e) {              e.printStackTrace();          }      }  }  

 

得到的运行结果如下：

i=2i=1testEx2, catch exceptiontestEx2, finally; return value=falsetestEx1, catch exceptiontestEx1, finally; return value=falsetestEx, finally; return value=false

  对比以上两段代码，不难发现，两个的主要区别只是一行语句的差别在于testEx2方法下最后一句：return ret;

通过调试不难得出这样的结论：即使在方法内捕捉到异常，如果在finally代码段中加入了返回值，那么异常将会被返回值屏蔽。