How do I copy some items of an array into another array?

By Wayan in Core API, Lang Package 0 Comment

In the code snippet below we are going to learn how to use the System.arraycopy() method to copy array values. This method will copy array from the specified source array, starting from the element specified by starting position. The array values will be copied to the target array, placed at the specified start position in the target array and will copy values for the specified number of elements.

The code snippet below will copy 3 elements from the letters array and place it in the results array. The copy start from the third elements which is the letter U and will be place at the beginning of the target array.

package org.kodejava.lang;

public class ArrayCopy {
    public static void main(String[] args) {
        // Creates letters array with 5 chars inside it.
        String[] letters = {"A", "I", "U", "E", "O"};

        // Create an array to where we are going to copy
        // some elements of the previous array.
        String[] results = new String[3];

        // Copy 3 characters from letters starting from the
        // third element and put it inside result array
        // beginning at the first element
        System.arraycopy(letters, 2, results, 0, 3);

        // Just print out what were got copied, it will
        // contains U, E, and O
        for (String result : results) {
            System.out.println("result = " + result);
        }
    }
}

The output of the code snippet:

result = U
result = E
result = O

How do I convert a collection object into an array?

By Wayan in Core API, Util Package 0 Comment

To convert collection-based object into an array we can use toArray() or toArray(T[] a) method provided by the implementation of Collection interface such as java.util.ArrayList.

package org.kodejava.util;

import java.util.List;
import java.util.ArrayList;

public class CollectionToArrayExample {
    public static void main(String[] args) {
        List<String> words = new ArrayList<>();
        words.add("Kode");
        words.add("Java");
        words.add("-");
        words.add("Learn");
        words.add("Java");
        words.add("by");
        words.add("Examples");

        String[] array = words.toArray(new String[0]);
        for (String word : array) {
            System.out.println(word);
        }
    }
}

Our code snippet result is shown below:

Kode
Java
-
Learn
Java
by
Examples

How do I convert an array into a collection object?

By Wayan in Core API, Util Package 0 Comment

To convert array based data into List / Collection based we can use java.util.Arrays class. This class provides a static method asList(T... a) that converts array into List / Collection.

package org.kodejava.util;

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

public class ArrayAsListExample {
    public static void main(String[] args) {
        String[] words = {"Happy", "New", "Year", "2021"};
        List<String> list = Arrays.asList(words);

        for (String word : list) {
            System.out.println(word);
        }
    }
}

The results of our code are:

Happy
New
Year
2021

How do I compare if two arrays are equal?

By Wayan in Core API, Util Package 0 Comment

Using Arrays.equals() methods we can compare if two arrays are equal. Two arrays are considered to be equal if their length, each element in both arrays are equal and in the same order to one another.

package org.kodejava.util;

import java.util.Arrays;

public class CompareArrayExample {
    public static void main(String[] args) {
        String[] abc = {"Kode", "Java", "Dot", "Org"};
        String[] xyz = {"Kode", "Java", "Dot", "Org"};
        String[] java = {"Java", "Dot", "Com"};

        System.out.println(Arrays.equals(abc, xyz));
        System.out.println(Arrays.equals(abc, java));
    }
}

The Arrays.equals() can be used to compare array of any primitive data type and array of Object. If you run this example you will have a result as follows:

true
false