CODEWITHSUNDEEP
javapost-increment
Elliott
Elliott

Reputation: 5609

Why does this cause an infinite loop

Consider this simple code:

 // E1 
  public void doTest(String pattern) {
    int counter = 0;

    while (counter < 3) {
        counter = counter++;
    }
    System.out.println("Done");
}

This causes an infinite loop.

However if the statement that increments the counter is written like this:

E2.  counter = ++counter;

or this

E3.    counter++;

It terminates normally. I understand that the incrementing occurs after the assignment in the version that fails which explains why E2 works, but I thought java assigned the results of an increment in the variable that is incremented as in E3. So I'm perplexed as to why E1 fails but E3 does not.

Upvotes: 5

Views: 1378

Answers (4)

fastcodejava
fastcodejava

Reputation: 41077

It is better to avoid this kind assignment. The ++ is intended to be used by itself. If you want to increment by yourself you could have done counter += 1.

Upvotes: 0

Abhishek
Abhishek

Reputation: 882

Replace 

 counter = counter++;

by: 1) 

counter+=1;

or

2)

counter++;

Cheers!

Upvotes: 1

Rohit Jain
Rohit Jain

Reputation: 213193

counter = counter++;

The above code has no effect on counter. It is effectively same as:

int temp = counter;
counter++;
counter = temp;

So, the value of counter is not changing at all.

On the other hand, if you use:

counter = ++counter;

The counter is incremented first, and then is re-assigned to counter. Essentially, you can simply ignore the assignment part, and keep it simply this:

counter++; // Or ++counter

Upvotes: 17

Mike Strobel
Mike Strobel

Reputation: 25623

The problem is that the value of counter at the end of the loop body is the same as it was at the beginning. The statement counter = counter++ is equivalent to:

int temp = counter;
counter = counter + 1;
counter = temp;

The postIncrement++ operator returns the value before the increment; the ++preIncrement operator returns the incremented value.

Upvotes: 2

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