Is it possible to write a loop in Java that does not actually use a loop method?

Question

I was curious if, in Java, you could create a piece of code that keeps iterating a piece of code without the use of a for or while loop, and if so, what methods could be used to solve this?

Answer 1

Look at recursion. A recursive function is a function which calls itself until a base case is reached. An example is the factorial function:

int fact(int n)
{
    int result;

    if(n==1)
        return 1;

    result = fact(n-1) * n;
    return result;
}

Answer 2

You could use the Java 8 Streams methods for iterating over the elements of a Collection. Among the methods you can use are filtering methods (get all the elements of a collection that satisfy some conditions), mapping methods (map a Collection of one type to a Collection of another type) and aggregation methods (like computing the sum of all the elements in a Collection, based on some integer member of the Element stored in the collection).

For example - Stream forEach :

List<Element> = new ArrayList<Element>();
...
list.stream().forEach (element -> System.out.println(element));

Or you can do it without a Stream :

List<Element> = new ArrayList<Element>();
...
list.forEach (element -> System.out.println(element));

Answer 3

Another variant of recursion:

public class LoopException extends Exception {
    public LoopException(int i, int max) throws LoopException {
        System.out.println( "Loop variable: "+i);
        if (i < max)
          throw new LoopException( i+1, max );
    }
}

Of course this is just a bit of fun, don't ever do it for real.

Answer 4

Java does not have a goto statement (that's a lie), so that way is a dead end.

But you could always make a piece of code endlessly iterate using recursion. Old factorial function seems to be the favorite, but since it is not an infinite loop, I will go for this simple function:

int blowMyStack(int a) {
    return blowMyStack(a + 1);
}

There will be many ways to do this using various features of the language. But it always falls to an underlying recursion.

Answer 5

In case you're referring of something like C's goto, the answer is no.

In other cases, you can use recursive functions.