Question

我想使用在文件中声明的变量，它是一个Function变量（接口）。对于函数的每个声明（每行一个），我想将它添加到函数表中。可能吗？是否有函数来检索代码中声明的变量？

感谢。

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

您可以使用ScriptEngine实例来评估函数并稍后调用：

    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"));

在此示例中打印

1.0。

如果您需要评估Java表达式，请查看JEXL：https://commons.apache.org/proper/commons-jexl/

Java - 如何使用在文本文件中声明的变量

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