Check if an exception instance is present in a generics array

Question

I want to check if an instance of a particular exception is present in a generics array. (I expect all elements of the array are to be some exceptions.)

Here's what I have tried:

class Ideone
{
    public static boolean isPresent(final Throwable t, final Class<?>[] exceptionArray){
        for(Class<?> exc : exceptionArray){
            if(t instanceof exc.getClass() ){
                return true;
            }
        }
    }
    public static void main (String[] args) throws java.lang.Exception
    {
        // your code goes here
        Class<?>[] my = {RuntimeException.class};
        isPresent(RuntimeException.class, my);
    }
}

Here's an IDEOne link if that helps you to simulate. Here, I get the error expected )

On IntelliJ Idea, on hovering, I get the error cannot resolve symbol 'getClass'.

Any Ideas?

Thanks.

flavio.donze · Accepted Answer · 2016-04-11T08:12:52.147

Try this code if you want to check the instance:

class Ideone {
    public static boolean isPresent(final Throwable t, final Class<?>[] exceptionArray) {
        for (Class<?> exc : exceptionArray) {
            if (exc.isAssignableFrom(t.getClass())) {
                return true;
            }
        }
        return false;
    }

    public static void main(String[] args) throws java.lang.Exception {
        // your code goes here
        Class<?>[] my = { RuntimeException.class };
        System.out.println("RuntimeException: " + isPresent(new RuntimeException(), my));
        System.out.println("IllegalStateException: " + isPresent(new IllegalStateException(), my));
        System.out.println("NoSuchMethodException: " + isPresent(new NoSuchMethodException(), my));
    }
}

Results in:

RuntimeException: true
IllegalStateException: true
NoSuchMethodException: false

Or this code if you want to check if the exception class matches:

class Ideone {
    public static boolean isPresent(final Throwable t, final Class<?>[] exceptionArray) {
        for (Class<?> exc : exceptionArray) {
            if (exc.equals(t.getClass())) {
                return true;
            }
        }
        return false;
    }

    public static void main(String[] args) throws java.lang.Exception {
        // your code goes here
        Class<?>[] my = { RuntimeException.class };
        System.out.println("RuntimeException: " + isPresent(new RuntimeException(), my));
        System.out.println("IllegalStateException: " + isPresent(new IllegalStateException(), my));
        System.out.println("NoSuchMethodException: " + isPresent(new NoSuchMethodException(), my));
    }
}

Results in:

RuntimeException: true
IllegalStateException: false
NoSuchMethodException: false

First mistake was passing RuntimeException.class instead of an instance new RuntimeException().
Second, exc is already a class object you don't need exc.getClass().
Third you did't not return false in case it did not find the exception.

Thanks. This looks good. Please add this link in the answer to help future visitors to this question: http://stackoverflow.com/questions/3949260/java-class-isinstance-vs-class-isassignablefrom — Akshay Arora, Apr 11 '16 at 08:02
The new one is better. The downsides of `isAssignableFrom` is that it will match all super classes. — Akshay Arora, Apr 11 '16 at 08:17

SomeJavaGuy · Answer 2 · 2016-04-11T08:11:41.423

you should change the variable t to represent a Class inheriting from Throwable. Your current implementation requires you to pass an instance of Throwable to the function, which is quite unnecessary if you want to check if a specific Exception is present. By changing it to Class<? extends Throwable> you can simply pass Exception.class and further on you just check if exc is assignable from t

public static boolean isPresent(final Class<? extends Throwable> t, final Class<?>[] exceptionArray){
    for(Class<?> exc : exceptionArray){
        if(exc.isAssignableFrom(t)){
            return true;
        }
    }
    return false;
}
public static void main (String[] args) throws java.lang.Exception
{
    // your code goes here
    Class<?>[] my = {RuntimeException.class};
    System.out.println(isPresent(RuntimeException.class, my));
    System.out.println(isPresent(IOException.class, my)); 
    System.out.println(isPresent(ArithmeticException.class, my));
}

output:

true
false
true

Check if an exception instance is present in a generics array

2 Answers2