ArrayList in Java

ArrayList in Java

Objectives

• Understand ArrayList in Java.

• Efficiently manage collections of objects.

• Enhance code readability.

• Improve program performance.

What is ArrayList?

• A resizable array.

• Also known as a Dynamic Array.

• In contrast to Array, ArrayList enables the user to use it without declaring the value and size as it automatically adjusts its capacity.

• It allows users to manipulate data inside the ArrayList by adding, removing, accessing, and changing the value of elements.

Methods that can be used in ArrayList

1. add() - Adds elements inside the ArrayList.

2. remove() – Removes an element using the index number.

3. get() – Accesses an element using the index number.

4. set() – Modifies an element referring to the index number.

5. clear() – Removes all elements in the ArrayList.

6. size() – Finds out how many elements are inside the ArrayList.

Creating an ArrayList

• Before using ArrayList, you need to import the package first:
  java import java.util.ArrayList;

• Initializing ArrayList, the TYPE here indicates the data type:
  java ArrayList<String> Name = new ArrayList<>();

Method Examples

1. add()

• Adds elements inside the ArrayList.

  package SampleForm;
  import java.util.ArrayList;
  public class ArrayListUsingAdd {
      public static void main(String[] args) {
          ArrayList<String> Name = new ArrayList<>();
          Name.add("Karina");
          Name.add("Winter");
          Name.add("Giselle");
          Name.add("Ningning");
          System.out.println(Name);
      }
  }
  

  Output:

  [Karina, Winter, Giselle, Ningning]
  

  Example using javax.swing.JFrame:

  package SampleForm;
  import java.util.ArrayList; // import
  public class ArrayListSample extends javax.swing.JFrame {
      public ArrayList<String> Color = new ArrayList<>(); //initialize arrayList
      String UserInput;
      public ArrayListSample() {
          initComponents();
      }
      @SuppressWarnings("unchecked")
      //Generated Code
      private void AddActionPerformed(java.awt.event.ActionEvent evt) {
          UserInput = UserField.getText();
          Color.add(UserInput);
          UserField.setText("");
          System.out.println(Color);
      }
  }
  

  Button Functionality:

  • Gets the value from the user and adds it to the ArrayList named Color.

2. get()

• Accesses an element using the index number.

  package SampleForm;
  import java.util.ArrayList;
  public class ArrayListUsingAdd {
      public static void main(String[] args) {
          ArrayList<String> Name = new ArrayList<>();
          Name.add("Karina");
          Name.add("Winter");
          Name.add("Giselle");
          Name.add("Ningning");
          String Display = Name.get(3);
          System.out.println(Display);
      }
  }
  

  Output:

  Ningning
  

  Button Functionality:

  • Gets the number from the user and displays the output according to its index.

  private void GetActionPerformed(java.awt.event.ActionEvent evt) {
      UserInput = UserField.getText();
      int value = Integer.parseInt(UserInput);
      System.out.println(Color.get(value));
  }
  

  Example:

  • ArrayList: [Anna, Sam]

  • Output if user inputs index 1: Sam

3. remove()

• Removes an element inside the ArrayList using the index number.

  Button Functionality:

  • Gets the user input and uses the method indexOf() to check the index of the inserted value and remove it.

4. set()

• Modifies an element referring to the index number.

  package SampleForm;
  import java.util.ArrayList;
  public class ArrayListUsingAdd {
      public static void main(String[] args) {
          ArrayList<String> Name = new ArrayList<>();
          Name.add("Karina");
          Name.add("Winter");
          Name.add("Giselle");
          Name.add("Ningning");
          Name.set(0, "Naevis");
          System.out.println(Name);
      }
  }
  

  Output:

  [Naevis, Winter, Giselle, Ningning]
  

  Button Functionality:

  • Adds value first on ArrayList and input the inserted value on first JOptionPane after that change the value.

  • Checks if there are changes in the ArrayList.

5. clear()

• Removes all elements in the ArrayList.

  package SampleForm;
  import java.util.ArrayList;
  public class ArrayListUsingAdd {
      public static void main(String[] args) {
          ArrayList<String> Name = new ArrayList<>();
          Name.add("Karina");
          Name.add("Winter");
          Name.add("Giselle");
          Name.add("Ningning");
          Name.clear();
          System.out.println(Name);
      }
  }
  

  Output:

  []
  

  Button Functionality:

  private void clearActionPerformed(java.awt.event.ActionEvent evt) {
      System.out.println("Previous ArrayList Values: " + Color);
      Color.clear();
      System.out.println("After clearing: " + Color);
  }
  

  Example:

  • Previous ArrayList Values: [a, v, c, d, e]

  • After clearing: []

6. size()

• Finds out how many elements are inside the ArrayList.

  package SampleForm;
  import java.util.ArrayList;
  public class ArrayListUsingAdd {
      public static void main(String[] args) {
          ArrayList<String> Name = new ArrayList<>();
          Name.add("Karina");
          Name.add("Winter");
          Name.add("Giselle");
          Name.add("Ningning");
          int ArrayListSize = Name.size();
          System.out.println(ArrayListSize);
      }
  }
  

  Output:

  4
  

  Button Functionality:

  • Gets the size of ArrayList depending on the added values.

    private void SizeActionPerformed(java.awt.event.ActionEvent evt) {
        int ArrayListSize = Color.size();
        System.out.println("ArrayList Size: " + ArrayListSize);
    }
    

  Example:

  • ArrayList: [INF231, INF232, INF233, INF234]

  • Output: ArrayList Size: 4