Java-如何使用文本文件中声明的变量

Question

I would like to use a variable declared in a fileknowing that it is a Function variable (interface). For each declaration of a function (one per line), I would like to add it to a function table. Is it possible ? Is there a function to retrieve the variables declared in the code ?

Thanks.

TestFunction.java

    ArrayList<Function> functions = new ArrayList<Function>();=

    Path file = Paths.get("./FunctionsDeclarations");
    try (InputStream in = Files.newInputStream(file);
        BufferedReader reader =
          new BufferedReader(new InputStreamReader(in))) {
        String line = null;
        while ((line = reader.readLine()) != null) {
            System.out.println(line);
    //Ex: line = "Function f = times(X, compose(SIN, times(constant(2.), X)));"
    //I want to use the Function variable f after the reading file : functions.add(f);
            new ScriptEngineManager().getEngineByName("js").eval(line);
        }
    } catch (IOException x) {
        System.err.println(x);
    }

FunctionsDeclarations

Function f = times(X, compose(SIN, times(constant(2.), X)));
Function f2 = times(X, compose(SIN, times(constant(8.), X)));
Function f3 = X;

Answer 1

You can eval functions and invoke later, using a ScriptEngine instance:

    ScriptEngineManager engineManager = new ScriptEngineManager();
    ScriptEngine engine = engineManager.getEngineByName("js");

    engine.eval("f = function() { return 1; }");

    Invocable invocable = (Invocable) engine;
    System.out.println(invocable.invokeFunction("f"));

1.0 is printed in this example.

If you need to evaluate Java expressions, take a look at JEXL: https://commons.apache.org/proper/commons-jexl/