How do I convert Set into Array?

package org.kodejava.example.util;

import java.util.*;

public class SetToArray {
    public static void main(String[] args) {
        // Create a java.util.Set object and add some integers into the Set.
        Set<Integer> numberSet = new HashSet<>();
        numberSet.add(1);
        numberSet.add(2);
        numberSet.add(3);
        numberSet.add(5);
        numberSet.add(8);

        // Converting a java.util.Set into an array can be done by creating a
        // java.util.List object from the Set and then convert it into an array
        // by calling the toArray() method on the list object.
        List<Integer> numberList = new ArrayList<>(numberSet);
        Integer[] numbers = numberList.toArray(new Integer[numberList.size()]);

        // Display the content of numbers array.
        for (int i = 0; i < numbers.length; i++) {
            Integer number = numbers[i];
            System.out.print(number + (i < numbers.length - 1 ? ", " : "\n"));
        }

        // Display the content of numbers array using the for-each loop.
        for (Integer number : numbers) {
            System.out.print(number + ", ");
        }
    }
}

How do I convert Set into List?

The code below gives you an example of converting a java.util.Set into a java.util.List. It simply done by creating a new instance of List and pass the Set as the argument of the constructor.

package org.kodejava.example.util;

import java.util.*;

public class SetToList {
    public static void main(String[] args) {
        // Create a Set and add some objects into the Set.
        Set<Object> set = new HashSet<>();
        set.add("A");
        set.add(10L);
        set.add(new Date());

        // Convert the Set to a List can be done by passing the Set instance into
        // the constructor of a List implementation class such as ArrayList.
        List<Object> list = new ArrayList<>(set);
        for (Object o : list) {
            System.out.println("Object = " + o);
        }
    }
}

How do I remove duplicate element from array?

This example demonstrates you how to remove duplicate elements from an array using the help of java.util.HashSet class.

package org.kodejava.example.util;

import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class ArrayRemoveDuplicate {
    public static void main(String[] args) {
        // A string array with duplicate values.
        String[] data = {"A", "C", "B", "D", "A", "B", "E", "D", "B", "C"};
        System.out.println("Original array         : " + Arrays.toString(data));

        // Convert a string array into java.util.List because we need a list
        // object to create the java.util.Set object.
        List<String> list = Arrays.asList(data);

        // A set is a collection object that cannot have a duplicate values,
        // by converting the array to a set the duplicate value will be removed.
        Set<String> set = new HashSet<>(list);

        // Convert the java.util.Set back to array using the toArray() method of
        // the set object copy the value in the set to the defined array.
        String[] result = set.toArray(new String[set.size()]);
        System.out.println("Array with no duplicate: " + Arrays.toString(result));
    }
}

The result of the code snippet above:

Original array         : [A, C, B, D, A, B, E, D, B, C]
Array with no duplicate: [A, B, C, D, E]

How do I convert Array to Set?

package org.kodejava.example.util;

import java.util.*;

public class ArrayToSetExample {
    public static void main(String[] args) {
        Integer[] numbers = {7, 7, 8, 9, 10, 8, 8, 9, 6, 5, 4};

        // To convert an array into a java.util.Set firstly we need to convert the
        // array into a java.util.List using the Arrays.asList() method. With the
        // List object created we can instantiate a new java.util.HashSet and pass
        // the list as the constructor parameter.
        List<Integer> numberList = Arrays.asList(numbers);
        Set<Integer> numberSet = new HashSet<>(numberList);

        // Or we can simply combine the line above into single line.
        Set<Integer> anotherNumberSet = new HashSet<>(Arrays.asList(numbers));

        // Display what we get in the set using iterator.
        for (Iterator<Integer> iterator = numberSet.iterator(); iterator.hasNext(); ) {
            Integer number = iterator.next();
            System.out.print(number + ", ");
        }

        // Display what we get in the set using for-each.
        for (Integer number : anotherNumberSet) {
            System.out.print(number + ", ");
        }
    }
}