Question

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Evaluating a math expression given in string form

How can I boolean evaluate a string containing bool expressions? Like:

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

The user should be able to define his own variables (a = 1), and define his own boolean expression (a & b & c). So I will have all expressions only as a string. How can I evaluate them?

Answer 1

You can use a ScriptEngine as commented by Nambari:

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));

prints 0.

Also note that the expression is not a boolean expression but a bitwise operation.