finally 语句块中, 最好不要使用return, 否则会造成已下后果;
1, 如果catch块中捕获了异常, 并且在catch块中将该异常throw给上级调用者进行处理, 但finally中return了, 那么catch块中的throw就失效了, 上级方法调用者是捕获不到异常的. 见demo如下:
1 public class TestException { 2 public TestException() { 3 } 4 5 boolean testEx() throws Exception { 6 boolean ret = true; 7 try { 8 ret = testEx1(); 9 } catch (Exception e) {10 System.out.println("testEx, catch exception");11 ret = false;12 throw e;13 } finally {14 System.out.println("testEx, finally; return value=" + ret);15 return ret;16 }17 }18 19 boolean testEx1() throws Exception {20 boolean ret = true;21 try {22 ret = testEx2();23 if (!ret) {24 return false;25 }26 System.out.println("testEx1, at the end of try");27 return ret;28 } catch (Exception e) {29 System.out.println("testEx1, catch exception");30 ret = false;31 throw e;32 } finally {33 System.out.println("testEx1, finally; return value=" + ret);34 return ret;35 }36 }37 38 boolean testEx2() throws Exception {39 boolean ret = true;40 try {41 int b = 12;42 int c;43 for (int i = 2; i >= -2; i--) {44 c = b / i;45 System.out.println("i=" + i);46 }47 return true;48 } catch (Exception e) {49 System.out.println("testEx2, catch exception");50 ret = false;51 throw e;52 } finally {53 System.out.println("testEx2, finally; return value=" + ret);54 return ret;55 }56 }57 58 public static void main(String[] args) {59 TestException testException1 = new TestException();60 try {61 testException1.testEx();62 } catch (Exception e) {63 e.printStackTrace();64 }65 }66 } 该方法的最终执行结果如下:
i=2
i=1testEx2, catch exceptiontestEx2, finally; return value=falsetestEx1, finally; return value=falsetestEx, finally; return value=false
尽管testEx2中的catch抛出异常, 但因为finally中return了, 那么testEx1中是捕获不到异常的, 所以testEx1中的catch块是不会执行的.
2, 如果在finally里的return之前执行了其它return , 那么最终的返回值是finally中的return:
public class TestException3 { public static int x = 3; int testEx() throws Exception { try { x = 4; return x; } catch (Exception e) { } finally { x = 5; return x; } } public static void main(String[] args) { TestException3 testException3 = new TestException3(); try { int a = testException3.testEx(); System.out.println(a); System.out.println(x); } catch (Exception e) { } }} 输出结果为5, 5
如果finally中的return被注释掉, 那么输出结果是4, 5