Java System API

Java system APIs live under sdk/java/picodroid/ and mirror the Android API surface; the java.* classes the SDK ships as source (java.time, java.util.Objects, java.util.zip.CRC32, …) sit beside them under sdk/java/java/. Native implementations are in crates/picodroid-core/src/native_handler/, and the built-in java.lang / java.util classes in crates/jvm/src/native/.

The reference is split by package family. Pick the area you need.

Area	Packages	Covers
Core language	java.lang, java.util, java.util.zip, java.time, java.io	String (incl. String.format, String.join), StringBuilder, Math, wrapper classes, exceptions, Random, ArrayList, HashMap / HashSet, Iterator / for-each, enums, Arrays / Collections / List / Comparable / Comparator, Objects, CRC32, java.time, the java.io streams (InputStream / OutputStream, BufferedReader, PrintWriter, …), Class, AutoCloseable, System.arraycopy, lambdas and method references
System & concurrency	picodroid.util, picodroid.os, picodroid.content.pm, picodroid.concurrent	Log, SystemClock, System.currentTimeMillis, Runtime (GC stats), Build, PackageManager / PackageInstaller, Thread and Object.wait / notify, Executors (main-thread FIFO + background pool), ScheduledExecutorService, ExecutorService / Future / Callable, the atomics, CountDownLatch, TimeUnit
Services & DI (Preview)	picodroid.app, picodroid.content, javax.inject, picodroid.di	Service / IBinder / Notification / NotificationManager, AlarmManager / PendingIntent (getActivity, getBroadcast), BroadcastReceiver / IntentFilter / registerReceiver / sendBroadcast, bindService / startService, ServiceConnection, compile-time DI (@Inject / @Singleton, @Module / @Provides, Provider<T> / Lazy<T>, automatic injection of Application / Activity / Service), manual DI components (ApplicationComponent, ActivitySingletonComponent)
Peripherals	picodroid.pio	PeripheralManager, Gpio (output and input), UartDevice, I2cDevice, SpiDevice, Pwm, Adc, AutoCloseable idiom
Storage	picodroid.io, picodroid.content, picodroid.os, picodroid.app.usage	File / FileInputStream / FileOutputStream (LittleFS), the per-app sandbox under /data/<package>, the Context private-file API, the storage reserve and per-app cap, StatFs, StorageStatsManager, SharedPreferences / Editor
Networking	picodroid.net	Socket, ServerSocket, DatagramSocket, DatagramPacket, InetAddress, NetworkInfo, ConnectivityManager + NetworkCallback / Network / NetworkCapabilities / NetworkRequest, HttpURLConnection + URL (Pico 2 W on hardware; sim always works)
JSON	picodroid.json	JSONObject, JSONArray, JSONException with Android’s org.json surface, over a native node pool (boards with has_json = true: every RP2350 board, not testbench_rp2040)
Protocol Buffers	picodroid.protobuf	CodedInputStream, CodedOutputStream, MessageLite, WireFormat, InvalidProtocolBufferException with protobuf-javalite’s surface over a native wire codec, plus protoc-gen-picodroid for message classes (boards with has_protobuf = true: every RP2350 board, not testbench_rp2040)
Sensors	picodroid.hardware	SensorManager, Sensor, SensorEvent, SensorEventListener — BME688 (temperature / humidity / pressure / gas), LTR559 (light / proximity)
Audio	picodroid.media	ToneGenerator with Android’s tone table, AudioManager stream constants — square-wave tones and melodies on a board’s piezo buzzer (boards with an [audio] section; no sampled audio anywhere)
Graphics & UI	picodroid.app, picodroid.graphics, picodroid.view, picodroid.widget, picodroid.debug	Application / Activity full lifecycle + back stack, Display / DisplayDebug, Color, Theme, GradientDrawable, View (incl. animate(), per-View touch, focus nav), ViewGroup, MotionEvent, GestureDetector, ViewPropertyAnimator, KeyEvent (with auto-repeat and long-press) / OnKeyListener / ViewConfiguration, OnSwipeListener, typed listener interfaces, the Adapter / ArrayAdapter pattern, 20+ widgets including Toast, AlertDialog, Keyboard, DatePicker, TimePicker, Snackbar, SwipeRefreshLayout, ImageView

Apps can be written in Kotlin against the same classes — see the Kotlin guide. What each Android and java.* API supports, and what it leaves out, is tabulated in the compatibility matrix.

Quick example

A complete mini-app that opens a GPIO pin, blinks it, and logs the result. See Peripherals for the full PIO surface and System & concurrency for Log and SystemClock.

package myapp;

import picodroid.util.Log;
import picodroid.os.SystemClock;
import picodroid.pio.PeripheralManager;
import picodroid.pio.Gpio;

public class MyApp {
    public static void main(String[] args) {
        PeripheralManager pm = PeripheralManager.getInstance();
        try (Gpio led = pm.openGpio("GP25")) {
            led.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);
            for (int i = 0; i < 5; i++) {
                led.setValue(true);
                SystemClock.sleep(500);
                led.setValue(false);
                SystemClock.sleep(500);
                Log.i("MyApp", "Blink " + String.valueOf(i + 1));
            }
        }
    }
}