要检测ARCore在前置摄像头上是否有效，您可以使用以下代码示例：

import android.app.Activity;
import android.content.Context;
import android.hardware.camera2.CameraAccessException;
import android.hardware.camera2.CameraCharacteristics;
import android.hardware.camera2.CameraManager;
import android.os.Bundle;
import android.util.Log;

import com.google.ar.core.ARCore;

public class MainActivity extends Activity {

    private static final String TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // 检查ARCore是否可用
        if (ARCore.isSupported()) {
            // 获取前置摄像头ID
            String frontCameraId = getFrontCameraId();
            if (frontCameraId != null) {
                // 检查前置摄像头是否支持ARCore
                boolean isSupported = ARCore.isDepthModeSupported(
                        this, CameraCharacteristics.LENS_FACING_FRONT, frontCameraId);

                if (isSupported) {
                    Log.d(TAG, "ARCore is supported on front camera");
                } else {
                    Log.d(TAG, "ARCore is not supported on front camera");
                }
            } else {
                Log.d(TAG, "Front camera not found");
            }
        } else {
            Log.d(TAG, "ARCore is not supported");
        }
    }

    private String getFrontCameraId() {
        CameraManager cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
        try {
            for (String cameraId : cameraManager.getCameraIdList()) {
                CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(cameraId);
                Integer lensFacing = characteristics.get(CameraCharacteristics.LENS_FACING);
                if (lensFacing != null && lensFacing == CameraCharacteristics.LENS_FACING_FRONT) {
                    return cameraId;
                }
            }
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
        return null;
    }
}

这段代码首先检查设备是否支持ARCore，然后获取前置摄像头的ID。接下来，使用ARCore.isDepthModeSupported()方法来判断前置摄像头是否支持ARCore。如果支持，将打印日志信息"ARCore is supported on front camera"，如果不支持，将打印日志信息"ARCore is not supported on front camera"。如果设备没有前置摄像头，将打印日志信息"Front camera not found"。如果设备不支持ARCore，将打印日志信息"ARCore is not supported"。

请注意，此代码示例仅适用于使用ARCore和Camera2 API的Android应用程序。确保已将ARCore和Camera2 API添加到您的项目依赖项中。