‘foreach’ statement is used to Traverse a Collection. Following example explains how to traverse a collection using for-each loop.
import java.util.Arrays;
import java.util.List;
public class Test {
public static void main(String args[]) {
ListString> list = Arrays.asList("Hi", "ptr", "How", "are", "you");
for (String s : list) {
System.out.println(s);
}
}
}
Output
Hi
ptr
How
are
you
To support for-each loop to your Custom collection, it should implement Iterable interface. In ‘Implement custom iterator in Java’ section, I explained about Iterable interface. . Suppose my collection has elements like 1, 2, 3, 4, 5, 6, 7, 8, 9. My for-each should traverse the elements at even positions like 1(is at 0th position), 3(is at 2nd position), 5, 7, 9.
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
public class EvenListT> implements IterableT> {
private ListT> list;
EvenList(ListT> list) {
this.list = list;
}
public IteratorT> iterator() {
return new EvenIteratorT>();
}
@SuppressWarnings("hiding")
private class EvenIteratorT> implements IteratorT> {
int size = list.size();
int currentPointer = 0;
public boolean hasNext() {
return (currentPointer size);
}
public T next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
@SuppressWarnings("unchecked")
T val = (T) list.get(currentPointer);
currentPointer += 2;
return val;
}
}
}
Total logic is in the next() method, here I am checking for an element in the collection using hasNext() method, it it returns false, I am throwing NoSuchElementException(). If element exists, then I am saving current element to a temporary variable and incrementing the currentPointer to 2.
import java.util.Arrays;
import java.util.List;
public class TestEvenList {
public static void main(String args[]) {
ListInteger> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
EvenListInteger> myList = new EvenList(list);
for(int i: myList){
System.out.println(i);
}
}
}
Run above application, you will get following output.
1
3
5
7
9
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This post first appeared on Java Tutorial : Blog To Learn Java Programming, please read the originial post: here
