Java - Check Not Null for a number, else assign default string value

Question

I am looking for a way to set the default value of a variable depending on whether a value is null or not.

The value in question is a double, and the default value (if that value is null) should be a string.

I tried using the following way but it failed because .orElse expects a double (aka same data type as "value"). Is there any Java methods that I can use to achieve that?

Double value = 8.0;
Optional.ofNullable(value).orElse("not found")

Answer 1

您不远，只需映射值即可：

String strDouble = Optional.ofNullable(value).map(Objects::toString).orElse("not found");

Answer 2

您编译的方法版本：

Object result = Optional.<Object>ofNullable(value).orElse("not found");

Answer 3

Since the left side of the the assignment operator can be either a Double or a String , the best that can be done is to specify its type as Object .

This will work:

Object value2 = Optional.<Object>ofNullable(value).orElse("not found");

(ie The only shared class in the class hierarchy for Double and String is Object)

Answer 4

That depends on what you want to do when you have null.

If you can use a default long value - then use your approach and instead of the string put the default value in the orElse .

If you just want to know if a null was passed, and if so do something different, but you don't want to have ==null , you can use the Optional::isPresent call inside an if .

If not having a value is not a state you can tolerate, you can use Optional::orElseThrow to throw an Exception.

Finally, if you just want to do something if you indeed have a value, take a look at Optional::ifPresent - it is the most fitting for this scenario.

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If you detail your use-case a bit more, I'll try to fine-tune this answer to fit better.

These are all the APIs for java 8, in later versions you have some more flexibility.