檢視 SCJP 1.6版考題 140 的原始碼

 Given:
 1. public class A{
 2.   public void method1(){
 3.     B b = new B();
 4.     b.method2();
 5.     //more code here
 6.   }
 7. }
 1. public class B{
 2.   public void method2(){
 3.     C c = new C();
 4.     c.method3();
 5.     //more code here
 6.   }
 7. }  
 
 
 1. public class C{
 2.   public void method3(){ 
 3.     //more code here
 4.   }
 5. }
 And given:
 25. try{
 26.   A a = new A();
 27.   a.method1();
 28. }catch(Exception e){
 29.   System.out.print("an error occurred");
 30. }
  
 
 Which two statements are true if a NullPointerException is thrown on line 3 of class C? (Choose two.)
  A. The application will crash.
  B. The code on line 29 will be executed.
  C. The code on line 5 of class A will execute.
  D. The code on line 5 of class B will execute.
  E. The exception will be propagated back to line 27.


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<span style="font-size:medium;">解答</span>

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<span style="font-size: medium;">Ans: B E   </span>

<span style="font-size:medium;"> 解說:
 當類別C中的第3行(method3)拋出NullPointerException 時 method3不正常結束後回到類別B的第4行(method2)，
 而method2並沒有處理這個例外而不正常結束，又回到類別A的method1方法，回到method1的呼叫者27行(E)，
 這個例外被28行的catch補捉到，執行第29行(B)
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{{SCJP 1.6版考題講解}}