ScriptJava
Java REPL today
There are a lot of benefits for a programming language to have a REPL. It helps one learn and explore the language features, gives ability to execute fast a code in question without launching IDE or modifiying existing project.
Writing whole Java code in command line seems like an overkill. Creating a class, then main method, then call to System.out.print()
to execute such simple as Integer.MAX_VALUE
command seems like a long way. What's why ScriptJava is not completely Java REPL. For example, semicolons( ;
) are mostly optional. There are a lot of build-ins methods, that can save a coder a few keyboard strokes. So, yeah, to know the value of Integer.MAX_VALUE
you just input Integer.MAX_VALUE
.
Build-in functions
bool()
-> inspired by python's function. In short:null
,0
, or""
(empty string) returnsfalse
. Defined inBool.java
len()
- > inspired by python's function. Unifies calls to get length of different objects. Defined inLength.java
str()
- > returns good object representation as a String. Defined inStr.java
. In case of a file (if exists) returns file contents as a Stringprint()
> do as expected. Accepts multiple objects:print(1, 2, 3, 4)
. Every object's string representation will be obtained viastr()
callprintf()
-> Helper method to callSystem.out.printf()
. Won't change the objects representationlist()
-> creates a list from supplied arguments,list(1, 2, 3, 4)
map()
-> original signature of this method is a bit scary:map(String[] keys, Object[] values)
, but with the help of the substitution command becomes more friendly:map(key1: 1, key2: 2)
bin()
-> returns binary representation of an integer valuehex()
-> return hex representation of an integer valuedate()
-> helper method to callnew Date()
now()
-> helper method to callSystem.currentTimeMillis()
exec()
-> executes supplied command as a String in a different process, returns String (the process output):exec("java -version")
file()
-> this method has different signatures. Called without parameters returns current execution folder. Called with a String as a parameter -> constructs File object with specified pathdel()
-> removes file, takes a File object or a pathwrite()
-> takes a File object and it's contents as a String. Will write contents to a filejson()
-> Super primitive json parser that returnsElement
with the following methods:key(String)
-> retrieves an JSON object by the key;at(int)
-> retrieves a value from JSON array at give index;get()
-> returns JSON primitive. Please note that exception will be thrown if method called on wrong JSON type (for exampleat
will be called on JSON object)get()
-> executes GET http request, returns response as a Stringpost()
-> executes POST http request, returns response as a Stringrange()
-> creates a range of integers to be easily interated,for (int i: range(10))
. Returnsint[]
. has 3 signatures:range(end)
,range(start, end)
,range(start, end, step)
dict()
-> returns object's meta info (class name, parent class name, implements), fields and values. Has ability to return also info about methodstype()
-> returns human readable Type info (redirects call tostr()
)toMap()
-> converts an object into aMap<String, Object>
(no recursive calls)fromMap()
-> constructs an object from suppliedMap<String, Object>
set()
-> tries to modify objects field given the name and value. Can modifyfinal
fieldsni()
-> simple call forClass.newInstance()
store()
-> stores a variable between script recompilations (actually can be useful only when removing previously retrieved value withret
call)ret()
-> retirievs previously stored valiable or tries to obtain it if not presentcopy()
-> copies supplied argument to the system clipboard and returns the value unmodified.copy(exec("echo HelloThere | cowsay -e --"))
will copy result value of theexec
call and print it.
Also, by default java.util.Math
is statically imported, so pow()
, sin()
, cos()
, etc are available
Special commands
import
-> adds an import statement for a script, for exampleimport java.text.*
clean
-> completely cleans scriptquit
-> exits from REPLbytecode
-> prints bytecode for current script (ifjavap
is present in PATH)
Substitutions
map(key1: 1, key2: 2, key3: "some string")
this (invalid in Java syntax) will be substituted new a call to build-in function map:map(new String[] { "key1", "key2", "key3" } , new Object[] { 1, 2, "some string" } )
ret("key", someCommand())
-> will be sustituted with:ret("key", new Provider() { Object provide() { return someCommand(); } } )
. This is done to skip initialization command if value is already defined, else the Provider object will be called to retrieve the value
Default imports
Except build-in functions these packages are imported by default:
java.util.*
java.text.*
java.io.*
Custom libraries
Right now if there is a folder called libs
inside execution directory, all jars that are inside it will be added to the script class path. Anyway you still need to import desired class first (here is no surprices).
Drawbacks
As we cannot achive completely scripting behavior from Java, there are certain things to be aware of. First, everytime you hit Enter
the whole script is compiled from scratch. That's why all the variables will be set anew. For example:
Date d = date() // hit Enter d // will print the *current* date, not the date value, that we obtained earlier
There is a woraround for this: build-in function ret
:
Date d = ret("d", date()) d // will print the first obtained value
Installation
Before launching the executable make sure, that there is javac
in the system PATH. Most likely that you already have it there. Also, if you wish to use bytecode
function (that prints Java bytecode of compiled script) make sure that there is also a javap
in the PATH.
Building
The main project has no dependencies, so it's a straight-forward process. However, building from IDE (when project is created from the source code) won't work, as current functionality requires the project's jar in the execution directory (due to build-in imports & IScript)
Tests require Gson
(for json testing)
License
Copyright 2016 Dimitry Ivanov ([email protected])
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.