使用ScriptEngine从String评估数学公式

这是我的代码:

double value = 2.55;
String formule = "x+x";

我想将句子中的x变量替换为value变量,所以我的下一个代码是:

formule = formule.replace("x", String.valueOf(value));
System.out.println(formule);

我已经0.0+0.0回到了终点站.

这是我的代码,其中x - > 0.0永远:

protected double Formule(Double Value) throws ScriptException
{
    String ValueString = Value.toString();
    ScriptEngineManager factory = new ScriptEngineManager();
    ScriptEngine engine = factory.getEngineByName("JavaScript");
    Double source = null;
    formule = formule.replace("sin", "Math.sin").
         replace("cos", "Math.cos").
         replace("tan", "Math.tan").
         replace("sqrt", "Math.sqrt").
         replace("sqr", "Math.pow").
         replace("log", "Math.log").
         replace("x", ValueString);
    try {
        source = (Double)engine.eval(formule);
    } catch(Exception exc) {
        JOptionPane.showMessageDialog(null, "Invalid input", "Error", JOptionPane.ERROR_MESSAGE);
    }
    this.repaint();
    return source;
}

解决!!!

我刚刚创建了名为的临时字符串tmp,现在看起来像这样

protected double Formule(Double Value) throws ScriptException
{       
    String tmp;
    tmp = formule.replace("sin", "Math.sin").
    replace("cos", "Math.cos").
    replace("tan", "Math.tan").
    replace("sqrt", "Math.sqrt").
    replace("sqr", "Math.pow").
    replace("log", "Math.log").
    replace("x", String.valueOf(Value));
    try {
        return (Double)engine.eval(tmp);
    } catch(Exception fexp) {
        return null;      
    }
    return 0;
}

因为String formule我班上是全局变量