[OCAJP][OCPJP]拋接例外

View the exhibit.

class MissingInfoException extends Exception {
}

class AgeOutofRangeException extends Exception {
}

class Candidate {

    String name;
    int age;

    Candidate(String name, int age) throws Exception {
        if (name == null) {
            throw new MissingInfoException();
        } else if (age <= 10 || age >= 150) {
            throw new AgeOutofRangeException();
        } else {
            this.name = name;
            this.age = age;
        }
    }

    public String toString() {
        return name + " age: " + age;
    }
}

Given the code fragment:

public class Test {
    public static void main(String[] args) {
        Candidate c = new Candidate("James", 20);
        Candidate c1 = new Candidate("Williams", 32);
        System.out.println(c);
        System.out.println(c1);
    }
}

Which change enables the code to print the following?

A.
Replacing line 5 with

public static void main (String [] args) throws MissingInfoException, AgeOutofRangeException {

B.
Replacing line 5 with

public static void main (String [] args) throws.Exception {

C.
Enclosing line 6 and line 7 within a try block and adding:

catch (MissingInfoException e1) { //code goes here
}
catch (AgeOutofRangeException e2) {//code goes here
}
catch(Exception e3) { //code goes here
}

D.
Enclosing line 6 and line 7 within a try block and adding:

catch (MissingInfoException e2) { //code goes here
}
catch (AgeOutofRangeException e3) {//code goes here
}

題解

原本題目提供的程式會在第6行和第7行出現編譯錯誤，原因在於Candidate的物件有拋出Exception。由於Exception是需要檢查的例外(checked exception)，因此必須要撰寫程式去處理它。

選項A，只讓main方法拋出MissingInfoException和AgeOutofRangeException是不夠的，必須要拋出Exception才行。

選項B，throws的用法錯誤。

選項C，有catch到Exception，正確選項。

選項D，只讓try-catch接住MissingInfoException和AgeOutofRangeException是不夠的，必須要接住Exception才行。