How and where to store expressions in variables

Question

Can I make expressions in Java and store them into a variable of Boolean datatype? So that I can use them in conditional use? If so please tell how.
Expressions like:
(temp.name(0) && temp.name(1))
and save them into a variable which can either be true or false.

Possible duplicate of [Is there an eval() function in Java?](http://stackoverflow.com/questions/2605032/is-there-an-eval-function-in-java) — ryanyuyu, Jan 09 '15 at 20:20

score 2 · Answer 1 · edited Jan 09 '15 at 20:41

2

Expressions themselves cannot be saved as a variable to be reused (like a function). You can do one of a few things:

1) Store the value of an expression

boolean nameValid = name.length() >= 1;

2) Define a method

public boolean isNameValid(String name) {
    return name != null && name.length() >= 1;
}

edited Jan 09 '15 at 20:41

Hoopje

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answered Jan 09 '15 at 20:19

Todd

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1

There are some scripting api can be used to parse the expressions. It is not impossible. – kosa Jan 09 '15 at 20:40
Yes, good call. However, I didn't include that because I felt that wasn't the intent of the question. But yeah, there are, and they do work if you need that sort of thing. – Todd Jan 09 '15 at 20:41

score 0 · Answer 2 · answered Jan 09 '15 at 20:27

You can use this approach if the condition execution time is very high, so you want to only calculate one time and store the result to use it after that many times. Thus, you save your time from repeating the calculation.

Example:

if (veryLongCalc() || someCond) {
   if (veryLongCalc()) {
      // veryLongCalc() will be called here 2 times
   } else { // someCond == true

   }
}

Can be better:

boolean b = veryLongCalc();
if (b || someCond) {
   if (b) {
      // veryLongCalc() only called once !!
   } else {

   }
}

How and where to store expressions in variables

2 Answers2