Java:如何检查对象是否为空? [英] Java: How to check if object is null?

问题描述

我正在创建一个从Web检索图像的应用程序.如果无法检索到图像，则应使用其他本地图像.

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

尝试执行以下行时:

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

如果drawable为null，则if(drawable.equals(null))行会引发异常.

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

有人知道应该如何检查drawable的值，以免在它为null的情况下不引发异常并检索本地图像(执行drawable = getRandomDrawable())?

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())?

推荐答案

已编辑的Java 8解决方案:

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

在这种情况下，您可以声明 drawable final .

You can declare drawable final in this case.

正如Chasmo指出的那样，Android目前不支持Java 8.因此，此解决方案仅在其他情况下可行.

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

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