为什么不能从 Java 执行包含 String[] 的 Julia 脚本

Question

public class ScriptProcess {

    private String[] command;

    public ScriptProcess(String[] c) {
        this.command = c;
    }

    public void exec() {
        try {
            Process p = Runtime.getRuntime().exec(this.command);
            BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream()));
            StringBuffer stringBuffer = new StringBuffer();
            String line = null;
            while((line = in.readLine()) != null){          
                stringBuffer.append(line + " --- ");
            }
            System.out.println(stringBuffer.toString());
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}

I can execute Julia script with this Java class.

For example, here is a julia script:

#main.jl
msgTest = Int64[]
push!(msgTest, 1)
push!(msgTest, 2)    
println(msgTest)

Then, I can initialize a ScriptProcess to execute the julia script above:

String[] command = {"C:\\Julia\\bin\\julia.exe", "C:\\doc\\Julia\\main.jl"};
ScriptProcess sp = new ScriptProcess(command);
sp.exec();

Everything's fine, I can get the result: [1,2] on the console of eclipse.

However, if I change the Int64 into String for the julia script like this:

#main.jl
msgTest = String[]
push!(msgTest, "aaa")
push!(msgTest, "bbb")    
println(msgTest)

And I run the same java project, I can't get anything.

However, I can run the julia script with command prompt:

C:\> C:\Julia\bin\julia.exe C:\doc\Julia\main.jl

I can get the result: AbstractString["aaa","bbb"] .

Answer 1

The new version Julia will generate a warning if String is used. String has been changed to AbstractString .

If we use String in Julia or some IDE of Julia, things will still be fine except a warning. However, if we want to execute a julia script with another language project, somehow we can't.

Answer 2

Since not a direct answer to the question, your example code is the base logic under an existing library, namely JuliaCaller, which is distributed with an open source license. You can pass Java objects to Julia, make calculations on the Julia side and get back the result into Java. Here is the link: JuliaCaller GitHub .

here is an example:

List<Double> values = List.of(1.0, 2.0, 10.0, -4.0);
caller.addJuliaObject(JuliaObject.createArrayVariable("a", values));
caller.Execute("using Statistics");
caller.Execute("ave = mean(a)");
double result = caller.getDouble("ave");
assertEquals(2.25, result);