cannot resolve Arrays.stream in android studio

Question

I am trying to use a lambda expression in Android Studio to filter an array

String[] a = { "s", "", "1", "", "" };
a = Arrays.stream(a).filter(s -> !s.isEmpty()).toArray(String[]::new);

I am getting an error on compilation 'Cannot resolve method stream'

Other Lambda expressions (say for click events) are working and I am targetting java 1.8 in my app gradle:

compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
    incremental = false;
}

Under File -> Project Stucture I am using the embedded JDK and even when I switch to the latest Java 8 JDK i still get the error.

Interestingly if i switch back to VERSION_1_7 then my prevously working lambda statements give a compile error.

How can I get this filter working in Android Studio?

Could there be an old rt.jar in your compiler configuration? — Paul Hicks, Oct 27 '16 at 03:24
@PaulHicks could you indicate where I check the compiler configuration? — wal, Oct 27 '16 at 03:27
[They don't](https://developer.android.com/guide/platform/j8-jack.html) — Sergey Gornostaev, Oct 27 '16 at 03:36
@SergeyGornostaev see my updated screenshot above please. the lambda compiles on android studio (and runs on android 5.1.1) but `Arrays.stream` doesnt — wal, Oct 27 '16 at 03:37
I think this is only an emulation. Maybe IDE change the lamdas to anonymous classes at compile time. Streams are more complex. — Sergey Gornostaev, Oct 27 '16 at 03:44

revau.lt · Accepted Answer · 2016-10-27T07:51:31.437

There is a difference between Java8 language features and Java8-API. Android supports only a subset of each. Lambdas are a Java8 language feature. Whereas the stream API is an API introduced in the Java8-API.

Language features are implemented by the compiler and might need some API-Support, whereas the Java-API needs to be present on the device.

This means you can use lambdas with apps having minSdkVersion < 24 but you can't use the stream API, since it is only part of the sdk for >=24.

https://developer.android.com/guide/platform/j8-jack.html#supported-features

You have the same in other "Java-technologies". Typically the Eclipse compiler can have a source compatibility of 1.8 and a target compatibility of 1.7, this would allow you to use lambdas, but not streams (when running on a java7 vm, on a java8 vm it would work)

cannot resolve Arrays.stream in android studio

1 Answers1