What does this method returns?

int a, b = 0;
try{
try{
a= 24/b;
}catch(ArithmeticException ex){
}finally{
a = -1;
b = 1;
}
}finally{
a = 0;
}
a = 24/b;
return a;

Question

What does this method returns?

int a, b = 0;
try{
    try{
        a= 24/b;
    }catch(ArithmeticException ex){
    }finally{
        a = -1;
        b = 1;
    }
}finally{
    a = 0;
}
a = 24/b;
return a;

BlackTom AI · Accepted Answer

Finally blocks execute regardless of whether an exception is thrown or caught, so tracking the sequence of assignments to a and b is key.

1) Relevant concepts
- Integer division and ArithmeticException when dividing by zero.
- try-catch-finally semantics in Java: the catch handles exceptions thrown in the try, and the finally always executes after the try (and any catch).
- The final value used by later statements depends on the assignments made in these blocks.

2) Step-by-step execution with variable states
Initial: int a, b = 0; so a is declared (not yet assigned), b = 0.

Enter outer try:
- Execute inner try: a = 24 / b; since b == 0, this throws ArithmeticException.
- Inner catch(ArithmeticException ex) executes and swallows the exception (empty body).
- Inner finally executes next: it sets a = -1; b = 1; so after inner finally: a = -1, b = 1.

Return to outer try: no more statements inside outer try, then outer finally executes:
- outer finally sets a = 0; now a = 0, b remains 1.

3) After try-finally blocks
Next statement: a = 24 / b;
- Now b == 1, so a = 24 / 1 = 24.
Return a; returns 24.

4) Why this answer is correct
Because the ArithmeticException from the first division is caught, the inner finally sets b to 1, and the outer finally sets a to 0 but does not change b. The final assignment a = 24 / b uses the updated b == 1, producing 24.

5) Why other plausible outcomes are wrong
- A runtime exception is not thrown at the end because the exception was caught and b was reset to 1 before the final division.
- Returning -1 or 0 would ignore the final assignment a = 24 / b which overwrites a with 24 after the finally blocks.

6) Conclusion
The method returns 24, which matches the provided correct answer "24".

What does this method returns? int a, b = 0; try{ try{ a= 24/b; }catch(ArithmeticException ex){ }finally{ a = -1; b = 1; } }finally{ a = 0; } a = 24/b; return a;单项选择题

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