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Learning Java: Using Array to Store Many Things

How to use Array
What will we do if we have a lot of data that will be stored in Vairabel?
Suppose we want to store the names of friends in a variable.
Then maybe we will do it like this:
String namaTeman1 = "Linda";
String namaTeman2 = "Santi";
String namaTeman3 = "Susan";
String namaTeman4 = "Mila";
String namaTeman5 = "Ayu";
This is fine.
However…
The problem is when there is a lot of data, for example there are 100 data, of course tired of not making that many variables.
Therefore, we can store it all in an array.
What is an Array?
An array is a variable that can store a lot of data in one variable.
Arrays use indexes to facilitate access to the data they store.
Example Array
The array index always starts from 0...
... and need to know also, the index is not always in the form of numbers. It can also be characters or text.

How to make arrays in Java

How to make an empty array:
// cara pertama
String[] nama;

// cara kedua
String nama[];

// cara ketiga dengan kata kunci new
String[] nama = new String[5];
Take note :
  • We use square brackets []to make arrays;
  • Square brackets can be placed after the data type or array name;
  • Numbers 5in parentheses means the limit or size of the array.
An empty array is ready to be filled with data. Be sure to fill it with data that matches the data type.
We can fill it like this:
nama[0] = "Linda";
nama[1] = "Santi";
nama[2] = "Susan";
nama[3] = "Mila";
nama[4] = "Ayu";
Or if you don't want to bother, you can create an array and fill it right away.
String[] nama = {"Linda", "Santi", "Susan", "Mila", "Ayu"};

Retrieving Data from Arrays

As we already know, arrays have an index to make it easier for us to access the data.
Therefore, we can retrieve the data in this way:
// membuat array
String[] nama = {"Linda", "Santi", "Susan", "Mila", "Ayu"};

// mengambil data array
System.out.println(teman[2]);
What do you think about the output?
Yep! really, the output is:
Susan
Because it is Susanlocated in the 2nd index.

Using looping

Retrieving data one by one from an array may be quite tiring, because we have to re-name the array with a different index.
Example:
System.out.println(teman[0]);
System.out.println(teman[1]);
System.out.println(teman[2]);
System.out.println(teman[3]);
What if the array data is up to 1000, then we have to type the code a thousand times.
Therefore, this is where the repetition plays.
Examples of arrays that are accessed by looping
Pay attention :
There we use attributes lengthto take the length of the array.
So, looping will be done as much as the contents of the array.

Now Let's Exercise

Please make a class named Buah, then follow the following code:
import java.util.Scanner;

public class Buah {
    public static void main(String[] args) {

        // membuat array buah-buahan
        String[] buah = new String[5];

        // membuat scanner
        Scanner scan = new Scanner(System.in);

        // mengisi data ke array
        for( int i = 0; i < buah.length; i++ ){
            System.out.print("Buah ke-" + i + ": ");
            buah[i] = scan.nextLine();
        }

        System.out.println("---------------------------");

        // menampilkan semua isi array
        for( String b : buah ){
            System.out.println(b);
        }

    }
}
The output results:
The output program array results
Pay attention :
There we use the foreach loop to display the contents of the array.
As we have learned in the Repetition material in Java , we can use this loop to display the contents of the array.

Multi Dimensional Arrays

Multi-dimensional arrays mean arrays that have more than one dimension.
Or we can call an array in an array.
The number of dimensions is unlimited, depending on how much we can 😄.
The following example is a two-dimensional array:
String[][] kontak = {
    {"Lili","08111"},
    {"Lala","08122"},
    {"Maya","08133"}
};
The index to the 0array kontakcontains an array {"lili","08111"}.
Two-dimensional array
Example of how to access data from a two-dimensional array:
Example of a 2-Dimensional Array in Java

Examples of Multi-Dimensional Array Programs

To make our understanding of multi-dimensional arrays even stronger, let's try to make a program.
Please create a new class named RuangKelasthen follow the following code:
import java.util.Scanner;

public class RuangKelas {
    public static void main(String[] args) {

        // Membuat Array dan Scanner
        String[][] meja = new String[2][3];
        Scanner scan = new Scanner(System.in);

        // mengisi setiap meja
        for(int bar = 0; bar < meja.length; bar++){
            for(int kol = 0; kol < meja[bar].length; kol++){
                System.out.format("Siapa yang akan duduk di meja (%d,%d): ", bar, kol);
                meja[bar][kol] = scan.nextLine();
            }
        }

        // menampilkan isi Array
        System.out.println("-------------------------");
        for(int bar = 0; bar < meja.length; bar++){
            for(int kol = 0; kol < meja[bar].length; kol++){
                System.out.format("| %s | \t", meja[bar][kol]);
            }
            System.out.println("");
        }
        System.out.println("-------------------------");
    }
}
The output results:
Results of the output of the 2d program array
In the program, we use nesting looping to take input and display its output .
Because a two-dimensional array is similar to a table, we must repeat the rows and columns.
Then what about 3D, 4D, 5D arrays, and so on?
Of course we have to make as many nesting loops as possible.
For three, yes for three repetitions.

Array List

The arrays that we discussed above actually have some disadvantages, such as:
  • Not able to store data of different types.
  • The size is not dynamic.
Therefore, there is an Array List that covers these shortcomings.
Array list is a class that allows us to create an object to hold anything.
To use the Array List, we must import it first.
import java.util.ArrayList;
After that, we can create an Array List object like this:
 ArrayList al = new ArrayList();
Let's try ...

Example Program with Array List

Please create a class with a name Doraemon, then follow the following code:
import java.util.ArrayList;

public class Doraemon {
    public static void main(String[] args) {

        // membuat objek array list
        ArrayList kantongAjaib = new ArrayList();

        // Mengisi kantong ajaib dengan 5 benda
        kantongAjaib.add("Senter Pembesar");
        kantongAjaib.add(532);
        kantongAjaib.add("tikus");
        kantongAjaib.add(1231234.132);
        kantongAjaib.add(true);

        // menghapus tikus dari kantong ajaib
        kantongAjaib.remove("tikus");

        // Menampilkan isi kantong ajaib
        System.out.println(kantongAjaib);

        // menampilkan banyak isi kantong ajaib
        System.out.println("Kantong ajaib berisi "+ kantongAjaib.size() +" item");
    }
}
The output results:
The output of the array list program output
Because array list ( kantongAjaib) is an object made from the Array List class, it has a method to do something.
  • Function add()to add something to the Array List;
  • Function remove()to delete something in the Array List;
  • Function size()to retrieve the size of the Array List;
  • Function get(id)to retrieve items in an Array List based on a particular ID or index.
  • and many other functions.
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