How Can a Variable Be Both 1 and 12? Exploring Impossible JS/Java Conditions

Recently I stumbled upon an intriguing post that posed the question: how can the JavaScript condition if(a == 1 && a == 12) ever evaluate to true? At first glance it seems impossible for a single variable to meet both conditions at once.

var a = ???;
if(a == 1 && a == 12){
  console.log(a);
}

After deeper thought, I realized the problem is interesting because it forces us to consider how a variable might change its value dynamically during evaluation.

Solution Overview

If we assume the condition can be true, the variable cannot be a normal primitive; it must be capable of altering its value on the fly.

JavaScript Version

One answer leverages object coercion tricks. The following image illustrates the approach:

This method may look baffling to Java or other OOP developers, but it demonstrates a viable way to satisfy the condition.

Java Version

The Java solution manipulates the internal Integer cache to make multiple integer instances reference the same value, allowing the same variable to appear equal to 1, 2, and 3 simultaneously:

Class cache = Integer.class.getDeclaredClasses()[0];
Field c = cache.getDeclaredField("cache");
c.setAccessible(true);
Integer[] array = (Integer[]) c.get(cache);
// array[129] is 1
array[130] = array[129]; // Set 2 to be 1
array[131] = array[129]; // Set 3 to be 1
Integer a = 1;
if(a == (Integer)1 && a == (Integer)2 && a == (Integer)3){
   System.out.println("Success");
}

Another more advanced answer uses PowerMockRunner to achieve the same effect, as shown in the following image:

Conclusion

The purpose of this article is not to deeply explore language internals, but to showcase a fun and thought‑provoking puzzle that tests both language‑specific knowledge and problem‑solving methodology.