Question

可能重复：
Evaluating a math expression given in string form

我如何布尔值计算包含bool表达式的字符串？像：

String userVar[] = {"a = 1", "b = 1", "c = 0"};
String expr = "a & b & c";
boolean result = evaluate(expr); //would evaluate to false

用户应该能够定义自己的变量（a = 1），并定义自己的布尔表达式（a & b & c）。所以我将所有表达式仅作为字符串。我该如何评估它们？

Answer 1

您可以使用Nambari评论的ScriptEngine：

ScriptEngine engine = new ScriptEngineManager().getEngineByName("JavaScript");
String userVar[] = {"a = 1", "b = 1", "c = 0"};

for (String s : userVar) {
    engine.eval(s);
}

String expr = "a & b & c";
System.out.println(engine.eval(expr));

打印0。

另请注意，表达式不是布尔表达式，而是按位运算。

Answer 2

最后，我为上述问题的解决方案制作了代码。

public static void main(String[] args) {
        String userVar[] = { "a = 1", "b = 0", "c = 1" };
        String expr = "a & b & c";

        // System.out.println(Boolean.valueOf("true"));
        Map<String, Boolean> booleanMap = getBooleanMap(userVar);
        // System.out.println(booleanMap);
        boolean evaluate = evaluate(booleanMap, expr);
        System.out.println("Final Result = " + evaluate);

    }

    public static boolean evaluate(Map<String, Boolean> operVal, String eq) {
        String[] split = eq.split(" ");
        boolean orgVal = false;
        boolean prevVal = false;
        boolean firstTime = true;
        String lastOpr = "&";
        for (String exp : split) {
            // System.out.println(orgVal + "  " + exp);
            // System.out.println(exp);
            if (exp.equals("&")) {
                lastOpr = "&";
                orgVal = orgVal && prevVal;
            } else if (exp.equals("|")) {
                lastOpr = "|";
                orgVal = orgVal || prevVal;
            } else {
                prevVal = operVal.get(exp);
                if (firstTime) {
                    orgVal = prevVal;
                    firstTime = false;
                }
            }
        }
        if (lastOpr.equals("&")) {
            lastOpr = "&";
            orgVal = orgVal && prevVal;
        } else if (lastOpr.equals("|")) {
            lastOpr = "|";
            orgVal = orgVal || prevVal;
        }

        // System.out.println(orgVal);
        return orgVal;
    }

    public static Map<String, Boolean> getBooleanMap(String[] val) {
        Map<String, Boolean> result = new HashMap<String, Boolean>();

        for (String exp : val) {
            String[] split = exp.split("=");
            // System.out.println(split[0].trim());
            // System.out.println(split[1].trim());
            String opr = split[0].trim();
            int intVal = Integer.valueOf(split[1].trim());
            boolean boolVal = false;

            if (intVal == 1) {
                boolVal = true;
            }

            result.put(opr, boolVal);

        }

        return result;

    }

测试用例 - 1

String userVar[] = {"a = 1", "b = 1", "c = 0"};

输出最终结果= false

测试用例 - 2

String userVar[] = { "a = 1", "b = 1", "c = 1" };

输出最终结果= true

评估布尔字符串表达式？

2 个答案: