NullPointerException, can I use throws because I "expect" code might crash because of NullPointerException?

Question

Can I declare my method with throws when code in method body might crash because of NullPointerException

I have code like a.getB().getC() inside this method

Edit:

I have tried with sample code,

class B {
    public void methodB() {}
}

class A {
    public void methodA(B b) throws NullPointerException {
        b.methodB();
    }
}

@Test
public void test_null_pointer() {
    boolean thrown1 = false;
    boolean thrown2 = false;
    A a = new A();

    try {
        B b = new B();
        a.methodA(b);
    } catch (NullPointerException n) {
        thrown1 = true;
    }

    try {
        a.methodA(null);
    } catch (NullPointerException n) {
        thrown2 = true;
    }

    assertFalse(thrown1);
    assertTrue(thrown2);
}

Test has succeeded.

Please go through these two pages - [How to ask a good question](https://stackoverflow.com/help/how-to-ask) and [How to create a Minimal, Complete, and Verifiable example](https://stackoverflow.com/help/mcve) — vinS, Dec 14 '17 at 06:13
It is not recommended to catch, but you can see this https://stackoverflow.com/a/15146645/5156075 — John Joe, Dec 14 '17 at 06:13

score 1 · Answer 1 · answered Dec 14 '17 at 06:18

Do your method throw the exception?

public static boolean getC() throws Exception{
    if(Some Condition)
        throw new Exception("Some Error");
    else
        return true;
}

or

public static boolean getC() throws Exception{
    try{
        ... Do Something ...
        return true;
    }catch(Exception e){
        throw e
    }
}

If it do, you can catch the exception when the method throw the exception back.

public static void main(String args[]){
    try{
        boolean isOK = getC(); 
    }catch(Exception e){
        System.out.println(e.getMessage());
    }
}

score 1 · Answer 2 · answered Dec 14 '17 at 06:29

You can use Optional

public YourObjectC getC(){
YOurObjectA a = new YourObjectA();
Optional<YourObjectC> opt = Optional.ofNullable(a)
                                    .map(YOurObjectA::getB)
                                    .map(YourObjectB::getC);

return opt.orElseThrow(NullPointerException::new);

}

Method will return object C but if object is null will throw Null Pointer exc

score 0 · Answer 3 · answered Dec 14 '17 at 06:30

You should not.

If this may be null, you must verify and apply your business rules in this case. Otherwise, I think is a good practice you to check if a must have parameter is null and then you throw an IllegalArgumentException. You can describe this behavior on your Javadoc, for instance. But to declare a method throws is useless.

NullPointerException, can I use throws because I "expect" code might crash because of NullPointerException?

3 Answers3