Java: How to check if object is null?


Question

I am creating an application which retrieves images from the web. In case the image cannot be retrieved another local image should be used.

While trying to execute the following lines:

Drawable drawable = Common.getDrawableFromUrl(this, product.getMapPath());
if (drawable.equals(null)) {
  drawable = getRandomDrawable();
}

The line if(drawable.equals(null)) throws an exception if drawable is null.

Does anyone know how should the value of drawable be checked in order not to throw an exception in case it is null and retrieve the local image (execute drawable = getRandomDrawable())?

1
70
8/17/2014 1:56:23 PM

Accepted Answer

Edited Java 8 Solution:

final Drawable drawable = 
    Optional.ofNullable(Common.getDrawableFromUrl(this, product.getMapPath()))
        .orElseGet(() -> getRandomDrawable());

You can declare drawable final in this case.

As Chasmo pointed out, Android doesn't support Java 8 at the moment. So this solution is only possible in other contexts.

33
10/20/2014 7:57:15 AM

Drawable drawable = Common.getDrawableFromUrl(this, product.getMapPath());
if (drawable == null) {
    drawable = getRandomDrawable();
}

The equals() method checks for value equality, which means that it compares the contents of two objects. Since null is not an object, this crashes when trying to compare the contents of your object to the contents of null.

The == operator checks for reference equality, which means that it looks whether the two objects are actually the very same object. This does not require the objects to actually exist; two nonexistent objects (null references) are also equal.


Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Icon