How do I shuffle elements of an array?

By Wayan in Core API, Util Package 0 Comment 
package org.kodejava.util;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class ArrayShuffle {
    public static void main(String[] args) {
        // Initialize the contents of our array
        String[] alphabets = {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J"};

        // As the Collections.shuffle() method need a list for the parameter
        // we convert our array into List using the Arrays class.
        List<String> list = Arrays.asList(alphabets);

        // Here we just simply used the shuffle method of Collections class
        // to shuffle out defined array.
        Collections.shuffle(list);

        // Run the code again and again, then you'll see how simple we do
        // shuffling
        for (String alpha : list) {
            System.out.print(alpha + " ");
        }
    }
}

An example of the generated results are:

F H E A B I G J D C

How do I know the minimum and maximum number in an array?

By Wayan in Core API, Util Package 0 Comment 
package org.kodejava.util;

import java.util.Arrays;
import java.util.Collections;

public class ArrayMinMax {
    public static void main(String[] args) {
        // Creates an array of integer numbers in it.
        Integer[] numbers = {8, 2, 6, 7, 0, 1, 4, 9, 5, 3};

        // To get the minimum or maximum value from the array we can
        // use the Collections.min() and Collections.max() methods.
        // But as this method requires a list type of data we need
        // to convert the array to list first.
        int min = Collections.min(Arrays.asList(numbers));
        int max = Collections.max(Arrays.asList(numbers));

        // Viola! we get the minimum and the maximum value from the
        // array.
        System.out.println("Min number: " + min);
        System.out.println("Max number: " + max);
    }
}

And here are the results:

Min number: 0
Max number: 9

How do I create an empty collection object?

By Wayan in Core API, Util Package 3 Comments

Sometimes you need to return an empty collection from your Java methods. The java.util.Collections utility class have three different static constants for creating empty List, Set and Map.

  • Collections.EMPTY_LIST
  • Collections.EMPTY_SET
  • Collections.EMPTY_MAP

There are also methods when you want to create type-safe empty collections.

  • Collections.emptyList()
  • Collections.emptySet()
  • Collections.emptyMap()

Bellow it the code example.

package org.kodejava.util;

import java.util.*;

public class EmptyCollectionDemo {
    public static void main(String[] args) {
        List list = Collections.EMPTY_LIST;
        System.out.println("list.size()  = " + list.size());
        Set set = Collections.EMPTY_SET;
        System.out.println("set.size()   = " + set.size());
        Map map = Collections.EMPTY_MAP;
        System.out.println("map.size()   = " + map.size());

        // For the type-safe example use the following methods.
        List<String> strings = Collections.emptyList();
        System.out.println("strings.size = " + strings.size());

        Set<Long> longs = Collections.emptySet();
        System.out.println("longs.size() = " + longs.size());

        Map<String, Date> dates = Collections.emptyMap();
        System.out.println("dates.size() = " + dates.size());
    }
}

The output are:

list.size()  = 0
set.size()   = 0
map.size()   = 0
strings.size = 0
longs.size() = 0
dates.size() = 0