关于java异常的一个小问题
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[待解决问题]
Thinking in Java 12章的一个例子. 刚开始看到的现象跟预期的不一样,我稍微改了一下.
1 class MyException2 extends Exception{ 2 private int x; 3 public MyException2(){ 4 super(); 5 } 6 public MyException2(String msg){ 7 super(msg); 8 } 9 public MyException2(String msg,int x){ 10 super(msg); 11 this.x = x; 12 } 13 public int val(){ 14 return x; 15 } 16 public String getMessage(){ 17 return "Detail Message: "+x+" "+super.getMessage(); 18 } 19 } 20 public class ExtralFeature { 21 public static void f() throws MyException2{ 22 System.out.println("Throwing MyExcetion2 from f()"); 23 throw new MyException2(); 24 } 25 public static void g() throws MyException2{ 26 System.out.println("Throwing MyExcetion2 from g()"); 27 throw new MyException2("Originated in g()"); 28 } 29 public static void h() throws MyException2{ 30 System.out.println("Throwing MyExcetion2 from h()"); 31 throw new MyException2("Originated in h()",47); 32 } 33 34 public static void main(String[] args) { 35 for(int i=0;i<5;i++){ 36 try { 37 f(); 38 } catch (MyException2 e) { 39 // TODO: handle exception 40 e.printStackTrace(); 41 } 42 try { 43 g(); 44 } catch (MyException2 e) { 45 // TODO: handle exception 46 e.printStackTrace(); 47 } 48 49 try { 50 h(); 51 } catch (MyException2 e) { 52 // TODO: handle exception 53 e.printStackTrace(); 54 System.out.println("e.val="+e.val()); 55 } 56 System.out.println("========================================"); 57 } 58 } 59 }
一个关于自定义异常的小例子. 刚开始我理解的,,mian方法中,执行到f()方法的时候,抛出异常,程序暂停,进入catch块中去处理. 完事儿之后返回,继续往下执行下一个try块中的g()方法,g()方法抛出异常之后,进入g()方法的catch块处理...所以我理解的输出应该是这个样子的
Throwing MyExcetion2 from f() ch12_Exception.MyException2: Detail Message: 0 null at ch12_Exception.ExtralFeature.f(ExtralFeature.java:25) at ch12_Exception.ExtralFeature.main(ExtralFeature.java:39) Throwing MyExcetion2 from g() ch12_Exception.MyException2: Detail Message: 0 Originated in g() at ch12_Exception.ExtralFeature.g(ExtralFeature.java:29) at ch12_Exception.ExtralFeature.main(ExtralFeature.java:45) Throwing MyExcetion2 from h() ch12_Exception.MyException2: Detail Message: 47 Originated in h() at ch12_Exception.ExtralFeature.h(ExtralFeature.java:33) at ch12_Exception.ExtralFeature.main(ExtralFeature.java:52) e.val=47 ======================================== ... ... ...
但是看输出结果貌似不是这个样子的,实际的输出是:
Throwing MyExcetion2 from f() Throwing MyExcetion2 from g() Throwing MyExcetion2 from h() e.val=47 ======================================== Throwing MyExcetion2 from f() Throwing MyExcetion2 from g() Throwing MyExcetion2 from h() e.val=47 ======================================== Throwing MyExcetion2 from f() Throwing MyExcetion2 from g() ch12_Exception.MyException2: Detail Message: 0 null at ch12_Exception.ExtralFeature.f(ExtralFeature.java:25) at ch12_Exception.ExtralFeature.main(ExtralFeature.java:39) ch12_Exception.MyException2: Detail Message: 0 Originated in g() at ch12_Exception.ExtralFeature.g(ExtralFeature.java:29) at ch12_Exception.ExtralFeature.main(ExtralFeature.java:45) ch12_Exception.MyException2: Detail Message: 47 Originated in h() at ch12_Exception.ExtralFeature.h(ExtralFeature.java:33) ... ... ...
所以就有点疑惑了,看上去像是多线程在执行. 刚学java,不是很懂. 是我理解错了吗? 还是说正确的应该是,main线程一直在执行,遇到f()方法抛出异常,将catch块交给另外一个线程,然后main这个线程会继续往下执行.
