Practice›Java Fundamentals›Module 6. Input, Files & Error Handling›(Optional) 6.5 Exceptions

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(Optional) 6.5 Exceptions — multiple catches and finally

Lesson

Optional lesson — beyond the AP CS A exam. Catching exceptions with try/catch is not on the AP exam (which only declares throws); this is here for a fuller picture of Java.

Several catches and finally

Different problems throw different exception types, and you can write a separate catch for each. A finally block, if present, runs no matter what — whether or not an exception happened — so it is used for cleanup.

Worked example

try {
    int n = Integer.parseInt(text);
    System.out.println(n);
} catch (NumberFormatException e) {
    System.out.println("Not a number");
} finally {
    System.out.println("Done");
}

If text is not a number, parseInt throws a NumberFormatException. Either way, finally prints Done.

▶ Try it: run this — it parses each input and always prints a Done line from finally.

String[] inputs = {"42", "oops", "7"};
for (int i = 0; i < inputs.length; i++) {
    try {
        int n = Integer.parseInt(inputs[i]);
        System.out.println("Parsed: " + n);
    } catch (NumberFormatException e) {
        System.out.println("Not a number: " + inputs[i]);
    } finally {
        System.out.println("Done with " + inputs[i]);
    }
}

A finally block runs...

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Integer.parseInt("oops") throws a...

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Type exactly what this program prints.

String[] in = {"5", "no"};
for (int i = 0; i < in.length; i++) {
    try {
        System.out.println("Parsed: " + Integer.parseInt(in[i]));
    } catch (NumberFormatException e) {
        System.out.println("Bad: " + in[i]);
    } finally {
        System.out.println("Done " + in[i]);
    }
}

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For different error types, you can have...

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True or false?

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