J2ME

J2ME games are the Java games that phones from Nokia, Sony Ericsson, Motorola, and others ran before smartphones. The optional J2ME content pak adds a J2ME system with its own Roms/J2ME/ folder, and the FreeJ2ME-Plus core that runs the games. The pak brings the Java runtime that core needs, so you don’t install anything else, and it doesn’t add an app to the Apps tab.

FreeJ2ME-Plus is the work of Paulo Sousa (AShiningRay), David Richardson (recompileorg), Saket Dandawate (hex007), and the FreeJ2ME-Plus contributors. The pak builds their code with a small patch so it runs from inside a pak.

Requires Leaf 0.13

The pak needs Leaf 0.13 or newer. Older releases don’t offer it in Pak Rat.

Install

Open System with the Menu button, go to Actions, then choose Pak Rat. Pick J2ME and install it over Wi-Fi. The download is about 38 MB, and the pak takes about 70 MB on the card, most of it Java. When the install finishes, J2ME appears with your other systems rather than in Apps.

The pak is open source and independently packaged in the J2ME-pak repository. It doesn’t include any games.

Add a game

Copy your games straight into Roms/J2ME/:

Roms/J2ME/
  Diamond Rush.jar
  Gravity Defied.jar

A J2ME game is a single .jar, sometimes with a .jad file beside it. You only need the .jar; Leaf ignores the .jad. Japanese KDDI games come as .kjx, which the core reads too. Don’t unzip either one: a .jar already is a zip, and the core reads it as it is. File names can be in any language: a game named in Chinese, Japanese, or Korean starts like any other.

Press MENU, then choose Actions → Rescan Library after copying games. For box art, put Images/J2ME/Diamond Rush.png beside the example above, named like the game, or let Leaf fetch it from ScreenScraper. ScreenScraper finds J2ME games by file name, so name each .jar after the game’s full title: Asphalt 4 Elite Racing.jar finds its art, but Asphalt 4.jar doesn’t. Anything in parentheses is ignored, so a name such as Diamond Rush (Gameloft) (1.0.1).jar works too. Phone games never came in boxes, so the box art ScreenScraper has for them is one it made from a screenshot. A game without box art shows the J2ME system icon.

A game takes about 6 to 9 seconds to start, because Java starts with it.

Delete Game isn’t offered for J2ME games, as for every system a content pak adds. Use Hide Game, or delete the file from your computer.

Controls

The buttons press the keys of a phone keypad:

Button	Phone key
D-pad	the arrow keys
A	OK / Fire, the center key
B	7
X	0
Y	9
L1 / R1	1 / 3
L2 / R2	* / #
Select / Start	left / right soft key
Left stick	2, 4, 6, 8
L3 (press the stick)	5

Most games need only the D-pad, A, and the soft keys, which are the two buttons under a phone’s screen. The number keys are there for games that use the whole keypad, like Doom II RPG. When a game says “press 5”, A usually works too.

Everything else matches Leaf’s other RetroArch cores.

• Menu opens Leaf’s in-game menu over the game; see The in-game menu. Choose Quit there to leave the game. Save State and Load State show No states, because this core can’t save states; see Saves.
• Menu held with another button works as it does on other cores. By default, Menu + Select opens the Game Switcher, and any RetroArch hotkey you’ve bound works the same way. See Hotkeys.

Games that ask you to touch the screen

Some later games were made for touchscreen phones and wait for a tap. Final Fantasy is one. FreeJ2ME gives these games a pointer, which follows the right stick by default. The MLP1 has only a left stick, so for each of these games, move the pointer to that stick:

1. Start the game and press MENU.
2. Open RetroArch Settings, then Quick Menu → Core Options → Advanced Settings, and set Pointer Stick to Left Stick.
3. Go back to Core Options, open Manage Core Options, and choose Save Game Options, so the change applies to this game only.

The left stick now moves the pointer, and pressing the stick (L3) taps where it points. Aim with the left stick, let go, then press L3 within about 3 seconds to tap. After that the pointer hides and L3 presses 5 again. Pressing any other button hides the pointer at once, so you can go back to the keys without waiting. While Pointer Stick is set, the left stick no longer presses 2, 4, 6, and 8, and the D-pad works as before.

A game is cut off or too small

Games are drawn at 240x320 by default, which suits most of them. Older Nokia games often want 176x208, touchscreen games often want 360x640, and a few landscape games want 640x480. A game that is cut off at the edges, sits small in a corner, or says it doesn’t support portrait mode needs a different resolution.

To set one for a single game:

1. Start the game and press MENU.
2. Open RetroArch Settings, then Quick Menu → Core Options → System, and change Phone Resolution.
3. Go back to Core Options, open Manage Core Options, and choose Save Game Options.
4. Quit the game and start it again. Until you do, it keeps drawing at the old size.

Larger resolutions are slower. Asphalt 4 at 640x480 plays, but at about 40 frames per second instead of 60.

A game stays on a white screen

Open RetroArch Settings, then Quick Menu → Core Options → Compatibility Settings, and set Repaint on MIDP Display setCurrent to Enabled. Save it as a game option the same way as the resolution, and restart the game. Need for Speed: Most Wanted needs this.

A game doesn’t start

FreeJ2ME-Plus doesn’t run every phone game, and a few never start; Nokia’s Bounce is one. The same game often exists in several builds for different phones, so another build of it may work.

Saves

Phone games save in their own menus, and there are no save states. Each game’s saves go to Saves/FreeJ2ME-Plus/freej2me/rms/, in a folder named after the game. Some games keep your place only when you leave through their own menu: Final Fantasy saves when you choose Quit in its menu. Leave a game that way before you choose Quit in Leaf’s in-game menu.

• FreeJ2ME’s own settings for each game go to Saves/FreeJ2ME-Plus/freej2me/config/.
• Core options, including the game options you save, are kept with the rest of Leaf’s RetroArch settings, in .umrk/mlp1/retroarch/ on your main card.
• FreeJ2ME also creates a freej2me_system/ folder in BIOS/ for its log.

Removing the pak removes the system on the next rescan. It doesn’t remove your files under Roms/, Images/, Saves/, or BIOS/.

How it works

Phone games are Java programs, and the MLP1 has no Java. The pak carries its own, Eclipse Temurin 17, cut down to the parts FreeJ2ME uses. When you start a game, the core starts that Java beside it, FreeJ2ME runs the game, and each frame goes to RetroArch. Starting Java is why a game takes a few seconds to appear, and why the pak is larger than most cores. Game text is drawn with the MLP1 firmware’s fonts, so Chinese, Japanese, and Korean games show their text too.

The pak sets a few defaults for a handheld: A is Fire, the green tint of an old phone screen is off, and music plays on two synthesizers instead of four, which starts games about half a second faster.