One cause of java.lang.StackOverflowError is a method calling itself without exit condition. The following Room class overrides toString method to produce more meaningful string representation, but is implemented wrong:

public class Room {
    public static void main(String args[]) {
        System.out.println("Created Room: " + new Room());
    }

    @Override public String toString() {
        return "Room: " + this.toString();  
        //change to super.toString() to avoid StackOverflowError
    }
}

Running Room class would fail with java.lang.StackOverflowError.