Skip to content

java_bridge.md

Latest commit

 

History

History
79 lines (68 loc) · 2.76 KB

java_bridge.md

File metadata and controls

79 lines (68 loc) · 2.76 KB

Java Bridge

Introduction

Java Bridge is a component that allows accessing Java resources (classes, objects, etc) in Lua. There are three types of resources:

  • Object (jobject) - any type of object, even a java.lang.Class object
  • Method (jmethod_id) - a reference to a method
  • Field (jfield_id) - a reference to a field

Note: All type signatures are in internal form. (I, [B, Ljava/lang/String;, etc)

Fields and Methods

Field and method references are represented in Java by the java.lang.reflect.Field and java.lang.reflect.Method classes. They reference a field or method of a class and are not associated with any instance of that class.

Field API

Fields contains the following properties:

  • name - field name
  • sig - signature
  • class - the class of which this field is a declared member
  • modifiers - a table of modifiers
  • enum synthetic volatile public private transient final static protected

Field references can be accessed through the Class.fields property:

yt> print(dump(java.lang.String.fields))
{
["CASE_INSENSITIVE_ORDER"] = jfield_id@0x7fc124002b00 java.lang.String.CASE_INSENSITIVE_ORDER type=Ljava/util/Comparator;,
["serialPersistentFields"] = jfield_id@0x7fc124003030 java.lang.String.serialPersistentFields type=[Ljava/io/ObjectStreamField;,
["HASHING_SEED"] = jfield_id@0x7fc1240012c0 java.lang.String.HASHING_SEED type=I,
["value"] = jfield_id@0x32 java.lang.String.value type=[C,
["hash"] = jfield_id@0x42 java.lang.String.hash type=I,
["serialVersionUID"] = jfield_id@0x7fc124003050 java.lang.String.serialVersionUID type=J,
["hash32"] = jfield_id@0x52 java.lang.String.hash32 type=I,
}

Static fields can be accessed directly on the class object:

yt> print(java.lang.String.fields.CASE_INSENSITIVE_ORDER.modifiers.static)
true
yt> print(java.lang.String.CASE_INSENSITIVE_ORDER)
jobject@0x7fc1240095d8: java.lang.String$CaseInsensitiveComparator@3bf0d7f5

Instance fields can be accessed directly on the object: (field access is not restricted)

yt> print(java.lang.String.fields.hash.modifiers.private)
true
yt> x = java.lang.String.new("xyz")
yt> print(x.hash) -- it's 0 until accessed
0
yt> print(x.hashCode())
119193
yt> print(x.hash)
119193

Method API

Methods contain the following properties:

  • name - method name
  • class -
  • sig -
  • args, ret -
  • modifiers -
  • line_number_table -
  • local_variable_table -

Objects

Objects are accessible by reference in a similar manner as in Java.

Examples:

  • Classes can be referenced by fully-qualified name:
  • > print(java.lang.String)
  • jobject@0x7fcdec0426d8: class java.lang.String
  • Objects can be instantiated by calling the new method on a class with appropriate constructor arguments:
  • uhmm... yeah... it needs some work