build-android-game-apk

SKILL: Build Android Game APK From Scratch

Philosophy

The smallest possible Android APK uses ZERO third-party libraries. Everything needed is already on the device inside android.jar. This skill produces a working game in ~16KB — compared to 5-15MB with Gradle + Kotlin + AndroidX.

Stack:

• Pure Java (no Kotlin — saves ~1MB Kotlin runtime)
• android.Canvas + SurfaceView for rendering (no game engine needed)
• MotionEvent for touch/swipe input
• android.jar only — no androidx, no dependencies
• Built manually: aapt2 → ecj → d8 → zip → zipalign → apksigner

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Project structure (minimal)

MyGame/
├── app/src/main/
│   ├── AndroidManifest.xml
│   ├── java/com/mygame/
│   │   ├── game/
│   │   │   └── GameLogic.java     ← pure game state, no Android imports
│   │   └── ui/
│   │       ├── GameView.java      ← SurfaceView + Canvas + touch
│   │       └── MainActivity.java  ← fullscreen setup, setContentView
│   └── res/values/
│       └── strings.xml            ← just app_name
└── AndroidManifest.xml            ← package, minSdk, activity

Key principle: separate game logic from rendering. GameLogic.java has zero Android imports — just plain Java. GameView.java handles all rendering and input.

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Step 1: Write the game logic (pure Java)

GameLogic.java — no Android imports at all:

package com.mygame.game;

import java.util.Random;

public class GameLogic {
    public static final int COLS = 10;
    public static final int ROWS = 20;

    // Game state fields
    public int[][] board;
    public int score = 0;
    public boolean gameOver = false;

    public GameLogic() {
        board = new int[ROWS][COLS];
        // initialize game...
    }

    // All game methods: move, rotate, collision, scoring
    public boolean moveLeft()  { /* ... */ return true; }
    public boolean moveRight() { /* ... */ return true; }
    public boolean moveDown()  { /* ... */ return true; }
    public void hardDrop()     { /* ... */ }
    public void rotate()       { /* ... */ }
}