How to make String as a condition in java

Question

Is there any way to make a string as a condtion in java.

Sample is shown below

class A {
    public static void main(String args[]) {

        B b = new B(10, 20);
        b.setCondition("val1>val2");
    }
}

class B {
    int val1 = 0;
    int val2 = 0;

    public B(int v1, int v2) {
        val1 = v1;
        val2 = v2;
    }

    public void setCondition(String condition){
   //the string should be evaluated as conditon like below.
     if(condition) ->  if(val1>val2)

   }
}

Is this is possibility in java. Thank you.

No, it's not possible, `if` should contain a statement that'll be evaluated to `true` or `false`, not a String. — Maroun, Feb 05 '15 at 07:42
possible duplicate of [Is there an eval() function in Java?](http://stackoverflow.com/questions/2605032/is-there-an-eval-function-in-java) — Jens, Feb 05 '15 at 07:43

score 0 · Answer 1 · answered Feb 05 '15 at 07:44

0

You have to implement your own parser, since Java code needs to be compiled. There is no evaluate() method, such as PHP or other scripting languages provide it.

answered Feb 05 '15 at 07:44

user1438038

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score 0 · Answer 2 · answered Feb 05 '15 at 07:48

Whatever is inside an if statement should evaluate to a boolean, in other words to true or false.

You want to be able to pass arbitrary conditions in String form, then you are gonna have to define a parser for your Strings.

If you really need to do this, which I kinda doubt for the record, consider defining a class that takes a String as constructor argument, two integer values to be evaluated and returns a boolean. Something like:

class Evaluator{
  public Evaluator(String condition){
    // parse condition
  }
  public boolean evaluate(int v1, int v2){ 
    // return true if condition is satisfied, false otherwise
  }
}

How to make String as a condition in java

2 Answers2