是否存在用于存储布尔表达式的数据结构？

Question

I need to store Boolean expressions like this:

x1 AND x2 AND x3 OR (x4 AND x5) AND (NOT x6)

Each x variable is a Boolean expression like == or != with values. The problem is to store nested AND and OR clauses (inside themselves and/or inside each other) and wrap them with NOT . The wrapping depth can be very deep.

Does the Java SDK have data structure for these expressions?

Answer 1

In Java 8 the functional interface Predicate<T> is the way to go.

Here are the Java docs .

And here are various examples .

So in your use case it will be something as follows:

public static Predicate<Integer> equals(Integer compare) {
    return i -> i.equals(compare);
}

public static Predicate<Integer> complex() {
    return equals(1).and(equals(2)).and(equals(3)).or(equals(4).and(equals(5))).and(equals(6).negate());
}

Remember — only Java 8 onwards!

Answer 2

You can try to use jexl ( http://commons.apache.org/jexl/ )

JexlEngine jexl = new JexlEngine();
    jexl.setSilent(true);
    jexl.setLenient(true);

    Expression expression = jexl.createExpression("(a || b && (c && d))");
    JexlContext jexlContext = new MapContext();

    //b and c and d should pass
    jexlContext.set("b",true);
    jexlContext.set("c",true);
    jexlContext.set("d",true);

    assertTrue((Boolean)expression.evaluate(jexlContext));

    jexlContext = new MapContext();

    //b and c and NOT d should be false
    jexlContext.set("b",true);
    jexlContext.set("c",true);

    //note this works without setting d to false on the context
    //because null evaluates to false

    assertFalse((Boolean)expression.evaluate(jexlContext));

Example from this question

ps: It is not included in standard sdk but quite easy to use.

Answer 3

abstract class Predicate {...}
class AndPredicate extends Predicate {
  private Predicate[] conjuncts;
  ...
}
class OrPredicate extends Predicate {
  private Predicate[] disjuncts;
  ...
}
class NotPredicate extends Predicate {
  Predicate negated;
  ...
}

What is the problem?