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4. ??

?????????????????????????????????????????????????????????????

4.1 ????

???????????????????????????????????????????????????????????????????????????????????????

???????????????????????????????????????????????????????????????????Java??????????

4.2 ??????

Java????????????????????????Throwable??Throwable?????????

• Error???????????????????????????????????????????????????????

• Exception???????????????????????????????Exception?????????

  • RuntimeException??????????????????????????????????????????????NullPointerException????????IndexOutOfBoundsException???????ArithmeticException??????????

  • Error?????????????????????

??????????????????????????????????????????????????????????

4.3 Exception???

???????????

?????????????????????????

4.4 ????

Java?????????????????????????

• RuntimeException
• ClassCastException????????????????????
• ArrayIndexOutOfBoundsException???????????????????
• NullPointerException???? null ????????????
• ArithmeticException
• IOException????????????????????????
• FileNotFoundException????????????
• EOFException???????????
• ClassNotFoundException??????????
• InterruptedException????????????
• SQLException????????????

?????????????????????????????

4.5 ????

????????????????Java????????????????

4.5.1 ????

??????????

try {
    // ?????????
    // ?????????????????catch?
} catch (ExceptionType1 e1) {
    // ??ExceptionType1?????
} catch (ExceptionType2 e2) {
    // ??ExceptionType2?????
} finally {
    // ???????
}

?????

• try???????catch??
• ??try???????????finally???????
• finally???????????? cleanup ???

???

public static void main(String[] args) {
    try {
        int[] arr = new int[3];
        System.out.println(arr[0]);
        System.out.println(arr[3]); // ?????ArrayIndexOutOfBoundsException
        System.out.println("over");
    } catch (ArrayIndexOutOfBoundsException e) {
        System.out.println("??????" + e.getMessage());
    } finally {
        System.out.println("?????");
    }
}

4.5.2 ??????

????????????????????????????????throws?????????

public void method() throws IOException {
    // ????IOException???
}

?????

• ?????????????????????????????????????
• ???????????????????????????????

4.5.3 ?????????

?Java??Throwable????????????????

• getMessage()??????????????
• toString()?????????????????
• printStackTrace()?????????????????????

4.6 ?????

????????????????????????????????????Exception?RuntimeException????

public class NoAgeException extends Exception {
    public NoAgeException(String message) {
        super(message);
    }
}
public class Person {
    private String name;
    private int age;
    public Person(String name, int age) throws NoAgeException {
        if (age < 0 || age > 200) {
            throw new NoAgeException("??????" + age);
        }
        this.name = name;
        this.age = age;
    }
}

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