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Possibilitys to iterate

Why does this not work? import java.util.Iterator; import java.util.LinkedList; public class MyClass { public static void main(String[ ] args) { LinkedList<String> animals = new LinkedList<String>(); animals.add("fox"); animals.add("cat"); animals.add("dog"); animals.add("rabbit"); for(int i=0; i<5; i++){ Iterator<String> it = animals.iterator(); String value = it.next(); System.out.println(value); } } } Reust is 5 times fox. But I want to iterate all values. Thanks!

22nd May 2020, 3:46 PM
Michael Herrmann
Michael Herrmann - avatar
13 Antworten
+ 1
iterator has hasNext() method which return boolean true if it has value to iterate.. u can use that in while loop condition
22nd May 2020, 3:57 PM
durian
durian - avatar
+ 1
You shloud write, assigning Iterator before the loop... And you have only 4 elements added so use i<4 or size() method return size of list... Iterator<String> it = animals.iterator(); for(int i=0; i< 4; i++){ //or use i<animals.size(); String value = it.next(); System.out.println(value);} Edit: Simple way,..! if just to display, not need to iterate : System.out.println(animals) ;
22nd May 2020, 3:59 PM
Jayakrishna ­čç«­čç│
+ 1
Simple way: for(String animal : animals) { System.out.println(animal); } Less simple: You can use an iterator. But then you have to loop while it has a next element, like Lily mentioned. Currently you do only access five times the first element.
22nd May 2020, 4:02 PM
Sandra Meyer
Sandra Meyer - avatar
+ 1
Iterator<String> it = animals.iterator(); // for(int i=0; i<5; i++){ for(int i=0; i<4; i++) { // Iterator<String> it = animals.iterator(); String value = it.next(); System.out.println(value); }
22nd May 2020, 4:17 PM
zemiak
+ 1
Sandra Meyer why? Maybe sometimes you don't have to iterate whole collection?
22nd May 2020, 6:04 PM
Michal
Michal - avatar
0
Iterating based on the length is acceptable for sololearn, but not for real projects.
22nd May 2020, 4:21 PM
Sandra Meyer
Sandra Meyer - avatar
0
Then I would prefer a stop condition. Iterating on the previously requested length is only secure if you are sure, that nobody and nothing could access the list in the meantime. This is usually given here, but not based on my project experience.
22nd May 2020, 6:27 PM
Sandra Meyer
Sandra Meyer - avatar
0
Sandra Meyer then you should use immutable collections if you worry about collection to be changed.
22nd May 2020, 6:30 PM
Michal
Michal - avatar
0
Could be a valid change, e.g. insertions. It's just not good style to use a counter, unnecessary additional variables and loop less secure where 2 clean valid implementations are given.
22nd May 2020, 6:35 PM
Sandra Meyer
Sandra Meyer - avatar
0
Sandra Meyer if there insertions happens, then size() method also returns changed size.. Is not it..?
22nd May 2020, 6:51 PM
Jayakrishna ­čç«­čç│
0
The size is only requested once with starting the loop. There are reasons why the for-each loop is called the enhanced for-loop. Iterator is another possibility but in fact not required here, because it is determined for completely other use cases. https://www.programiz.com/java-programming/enhanced-for-loop
22nd May 2020, 7:41 PM
Sandra Meyer
Sandra Meyer - avatar
0
And here a quite useful explanation what iterator is used for: http://www.javapractices.com/topic/TopicAction.do?Id=125
22nd May 2020, 7:42 PM
Sandra Meyer
Sandra Meyer - avatar
0
Thank you guys!
23rd May 2020, 11:19 AM
Michael Herrmann
Michael Herrmann - avatar