Luaj++

Introduction

A modified version of luaj by nirenr, adding better support for Java. The following content is from the NeLuaj Luaj++ reference manual, hoping it helps you understand luaj++.

Entry Files

Activity main.lua

Service service.lua

AccessibilityService accessibility.lua

NotificationListenerService notification.lua

WallpaperService wallpaper.lua

Services can use setLuaDir(dir) to set the running directory, setEnabled(context) to open the service settings interface, and getInstance() to get the service instance.

Omit Non-Essential Keywords

• Omit then

if a then

end

-->

if a

end

• Omit do

while a do

end

-->

while a

end

• Omit in

for k,v in pairs(t) do

end

-->

for k,v pairs(t)

end

• Omit function

local function a()
    
end

-->

local a()

end

• Support switch

switch a
  case 1,3,5,7,9
    print(1)
  case 2,4,6,8
    print(2)
  case 0
    print(0)
  default
    print(nil)
end

• Support when

a = when a
   case 1,3,5,7,9
     return 1
   case 2,4,6,8
     return 2
   case 0
     return 0
   default
     return nil
 end

• Support continue

for n = 1,10
  if n%2 == 0
    continue
  end
  print(n)
end

Support foreach

for k,v : t
end

for k,v in t
end

Support defer

defer statements will run when the function ends. Multiple defers run in LIFO (Last In First Out) order.

Support ? Operator

?a print(1)`print(2)
a = ?a print(1)`print(2)

Support Ternary if

b = if a 1 else 2
print(b)

Support try-catch-finally

try
  error("err")
catch(e)
  print("catch", e)
finally
  print("finally")
end

Support lambda, can use backslash to replace lambda keyword

lambda a,b->a+b

lambda a,b=>print(a+b)

lambda a,b:print(a+b)

lambda () -> print("lambda")

Support import

import "package"
-- Imports package and sets as local variable

import "java.lang.String"
-- Returns javaClass

import "java.lang.*"
-- Returns javaPackage

import str "java.lang.String"
-- Set alias

import "java.lang. *", "java.io.* "
-- Import multiple packages or classes at once

Support module

module has its own environment, default setting environment table metatable to itself.

module "name"

Support Self-Assignment local

local:print

Sets global print as local print.

Operator Optimization

!= can replace ~=
！ can replace not
&& can replace and
|| can replace or

Support Bitwise Operations

• Bitwise AND a=1&2
• Bitwise OR a=1|2
• Bitwise XOR a=1~2
• Right Shift a=1>>8
• Left Shift a=8<<2
• Bitwise NOT a=~2

Support 64-bit Integers

i=0xffffffffff

Support += -= *= /= %= ^= //= &= |= ~= <<= >>= ..= operations

a+=1
a-=1
a*=1
a/=1

Java Call Optimization

• javaClass Extension Functions/Properties

Object.array{} -- Create array
print(Object.new) -- Class constructor
print(Object.class) -- Get class itself
Object.override{} -- Override methods

• Direct () to build instance or implement interface/abstract class

b = ArrayList()
m = HashMap()
i = interface { 
    methodName=function(arg)
    end
}
c = abstract {
    methodName=function(super, arg)
    end
}

• Support Override Methods

list = ArrayList.override {
  function add(superCall, arg)
    superCall(arg)
  end
}()
list = ArrayList {
  add = function(s, a)
  end
}

• Support Metamethods

function Button:print()
  print(self)
end
Button(this):print()

• Support Batch Property Setting

Button(this) {
  text="test",
  enabled=false
}

• Direct Array Creation

i=int[10]
i=int{1,2,3}
i=Integer[10]

• Java Method Call using .

b.add(!)

• is Method Shorthand

view.isActivated()
-->
view.Activated

• Java getter/setter Optimization

b.setText("")
-->
b.text=""
m.abc=1

t=b.getText()
-->
t=b.text
t=m.abc

• Syntactic Sugar Example

  mBtn.setOnClickListener(View.OnClickListener {
    onClick = function(v)
      print(v)
    end
  })
  --> Ignore interface type
  mBtn.setOnClickListener({
    onClick = function(v)
      print(v)
    end
  })
  --> Shorthand functional interface
  mBtn.setOnClickListener(function(v)
    print(v)
  end)
  --> Shorthand this class method
  mBtn.onClick = function(v)
    print(v)
  end

• Array Operations

Use # to get length of common Java data types
Use ["index"] or .index to access array directly

• Index Optimization

t={}
t."end"=123
t.end=123

• Non-essential Interface Types Can Be Omitted

mViewPager.addOnPageChangeListener(
  ViewPager.OnPageChangeListener{
    onPageSelected = function(_)
    end
  }
)
-->
mViewPager.addOnPageChangeListener{
  onPageSelected = function(_)
  end
}

• Functional Interfaces Can Be Shortened

obj.run(Runnable {
  run = function()
    -- do something
  end
})
-->
obj.run(function()
  -- do something
end)

Support Enhanced String Formatting

a/A Signed hexadecimal float,

b Boolean,

B Unsigned byte,

c char type, number to character,

i/d Signed integer type, string to decimal,

I Unsigned int integer,

e/E/f/g/G Signed float,

o Octal signed integer,

L Unsigned long integer,

u/U String to unicode,

x/X Hexadecimal signed integer, string to hex,

r Parse string escape,

q Format as valid string form,

s To string,

l url encode,