What is the better way of generating levels in android game using LibGDX

What is the better way of generating levels in android game using LibGDX

I downloaded the source code of metagun for android from https://github.com/libgdx/libgdx/tree/master/demos/metagun/metagun-android
The game uses a png image to create the level. It uses the following code ...I am finding difficulties in understanding it well...the following code inside the Level.java
@SuppressWarnings("unchecked") public Level (GameScreen screen, int w, int h, int xo, int yo, int xSpawn, int ySpawn) { this.screen = screen; this.xSpawn = xSpawn; this.ySpawn = ySpawn;
    walls = new byte[w * h];
    entityMap = new ArrayList[w * h];
    this.width = w;
    this.height = h;

    for (int y = 0; y < h; y++) {
        for (int x = 0; x < w; x++) {
            entityMap[x + y * w] = new ArrayList<Entity>();

            int col = (Art.level.getPixel(x + xo * 31, y + yo * 23) & 0xffffff00) >>> 8;
            byte wall = 0;

            if (col == 0xffffff)
                wall = 1;
            else if (col == 0xFF00FF)
                wall = 2;
            else if (col == 0xffff00)
                wall = 3;
            else if (col == 0xff0000)
                wall = 4;
            else if (col == 0xB7B7B7)
                wall = 5;
            else if (col == 0xFF5050)
                wall = 6;
            else if (col == 0xFF5051)
                wall = 7;
            else if (col == 0x383838)
                wall = 8;
            else if (col == 0xA3FFFF)
                wall = 9;
            else if (col == 0x83FFFF) {
                BossPart prev = new Boss(x * 10 - 2, y * 10 - 2);
                int timeOffs = random.nextInt(60);
                ((Boss)prev).time = timeOffs;
                add(prev);
                for (int i = 0; i < 10; i++) {
                    BossNeck b = new BossNeck(x * 10 - 1, y * 10 - 1, prev);
                    b.time = i * 10 + timeOffs;
                    prev = b;
                    add(prev);
                }
            } else if (col == 0x80FFFF) {
                Gremlin g = new Gremlin(0, x * 10 - 10, y * 10 - 20);
                g.jumpDelay = random.nextInt(50);
                add(g);
            } else if (col == 0x81FFFF) {
                Gremlin g = new Gremlin(1, x * 10 - 10, y * 10 - 20);
                g.jumpDelay = random.nextInt(50);
                add(g);
            } else if (col == 0x82FFFF) {
                Jabberwocky g = new Jabberwocky(x * 10 - 10, y * 10 - 10);
                g.slamTime = random.nextInt(30);
                add(g);
            } else if (col == 0xFFADF8) {
                add(new Hat(x * 10 + 1, y * 10 + 5, xo * 31 + x, yo * 23 + y));
            } else if ((col & 0x00ffff) == 0x00ff00 && (col & 0xff0000) > 0) {
                add(new Sign(x * 10, y * 10, col >> 16 & 0xff));
            } else if (col == 0x0000ff) {
                // if (xSpawn == 0 && ySpawn == 0) {
                this.xSpawn = x * 10 + 1;
                this.ySpawn = y * 10 - 8;
                // }
            } else if (col == 0x00FFFF) {
                Gunner e = new Gunner(x * 10 + 2, y * 10 + 10 - 6, 0, 0);
                e.chargeTime = random.nextInt(Gunner.CHARGE_DURATION / 2);
                e.xa = e.ya = 0;

                add(e);