In Android Java, how do I check if a foldable device is flat or folded?

Question

Following a tutorial in https://developer.android.com/guide/topics/large-screens/make-apps-fold-aware, which is in Kotlin, I'm attempting to use it in Java. I have issues with the library not being recognised. One of many compilation errors is: Cannot resolve method 'getInstance' in 'WindowManager'. Does anyone know how to check if a device is flat or folded in Android Java?

This is my code, but there are lots of compilation errors indicating the new library is not brought in.

build.gradle

implementation 'androidx.window:window:1.0.0'  

In Activity which extends AppCompactActivity

import androidx.window.layout.FoldingFeature;
import androidx.window.layout.WindowLayoutInfo;
import androidx.window.layout.WindowMetrics;
import androidx.window.WindowManager;

        WindowManager windowManager = WindowManager.getInstance(this);
        LiveData<WindowLayoutInfo> layoutInfoLiveData = windowManager.getWindowLayoutInfo();
        layoutInfoLiveData.observe(this, new Observer<WindowLayoutInfo>() {
            @Override
            public void onChanged(WindowLayoutInfo windowLayoutInfo) {
                List<FoldingFeature> foldingFeatures = windowLayoutInfo.getDisplayFeaturesOfType(FoldingFeature.class);
                if (!foldingFeatures.isEmpty()) {
                    // This is a foldable device
                    FoldingFeature foldingFeature = foldingFeatures.get(0);

                    switch (foldingFeature.getState()) {
                        case FoldingFeature.State.FLAT:
                            // The device is currently flat/unfolded
                            break;
                        case FoldingFeature.State.HALF_OPENED:
                            // The device is half-opened (like a laptop)
                            break;
                        case FoldingFeature.State.FOLDED:
                            // The device is fully folded
                            break;
                    }
                }
            }
        });