Get reverse iterator for the given array in Java

Write a method that takes an array as input and return the reverse iterator.

 

Signature

public static <T> Iterator<T> reverseIterator(T[] array)

Define ArrayReverseIterator

 

ArrayReverseIterator.java

package com.sample.app.iterators;

import java.util.Iterator;
import java.util.NoSuchElementException;

public class ArrayReverseIterator<T> implements Iterator<T>, Iterable<T> {

	private final T[] array;
	private int currentIndex;

	public ArrayReverseIterator(T[] array) {
		if (array == null) {
			throw new IllegalArgumentException("Array can't be null to get an interator");
		}

		this.array = array;
		final int length = array.length;
		currentIndex = length > 0 ? (length - 1) : -1;
	}

	@Override
	public boolean hasNext() {
		return currentIndex > -1;
	}

	@Override
	public T next() {
		if (currentIndex <= -1) {
			throw new NoSuchElementException();
		}
		return array[currentIndex--];
	}

	@Override
	public void remove() {
		throw new UnsupportedOperationException();
	}

	@Override
	public Iterator<T> iterator() {
		return this;
	}
}

 

Use ArrayReverseIterator to read the array elements from last.

ArrayReverseIteratorDemo.java

package com.sample.app.arrays;

import java.util.Iterator;

import com.sample.app.iterators.ArrayReverseIterator;

public class ArrayReverseIteratorDemo {

	public static <T> Iterator<T> reverseIterator(T[] array) {
		return new ArrayReverseIterator<T>(array);
	}

	public static void main(String[] args) {
		ArrayReverseIterator<Integer> iterator = (ArrayReverseIterator) reverseIterator(new Integer[] { 2, 3, 5, 7, 11 });

		for (Integer ele : iterator) {
			System.out.println(ele);
		}
	}

}

 

Output

11
7
5
3
2

 

  

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