JAVA EE: Java Tutorial : Java inner class example

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DataStructure.java

public class DataStructure
{

    // Create an array
    private final static int SIZE = 6;
    private int[] arrayOfInts = new int[SIZE];

    public DataStructure()
    {
        // fill the array with ascending integer values
        for (int i = 0; i < SIZE; i++)
        {
            arrayOfInts[i] = i;
        }
    }

    public void printOdd()
    {

        // Print out values of even indices of the array
        DataStructureIterator iterator = this.new OddIterator();
        while (iterator.hasNext())
        {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();
    }

    interface DataStructureIterator extends java.util.Iterator<Integer>
    {
    }

    // Inner class implements the DataStructureIterator interface,
    // which extends the Iterator<Integer> interface
    // we can use inner classes to implement helper classes.

    private class OddIterator implements DataStructureIterator
    {

        // Start stepping through the array from the beginning
        private int nextIndex = 1;

        public boolean hasNext()
        {

            // Check if the current element is the last in the array
            return (nextIndex <= SIZE - 1);
        }

        // Return the odd element.
        public Integer next()
        {
            Integer retValue = Integer.valueOf(arrayOfInts[nextIndex]);
            nextIndex += 2;
            return retValue;
        }
    }

}

InnerClassTest.java

public class InnerClassTest
{

    public static void main(String s[])
    {

        // Fill the array with integer values and print out only
        // values of even indices
        DataStructure ds = new DataStructure();
        ds.printOdd();
    }

}

Output