.set()

In Java, the .set() method replaces the element present at a specified position with another element in an ArrayList. After execution, the method returns the replaced element.

Understanding how .set() works is crucial when dealing with mutable lists in Java, especially when updating or modifying elements during processing.

Syntax

arrayList.set(index, element);

Parameters:

• index: The position in the list where the element should be replaced.
• element: The new element that will replace the old one at the given index.

Return value:

The .set() method returns the replaced element.

Note: The element must be of the same data type as the rest of the elements in the arrayList. Otherwise, an error will occur.

Example 1: Basic Usage of .set()

This example uses the .set() method to replace elements at multiple positions in an ArrayList:

import java.util.ArrayList;

public class Students {
  public static void main(String[] args) {
    // Create an ArrayList
    ArrayList<String> studentList = new ArrayList<String>();

    // Add values to the ArrayList
    studentList.add("John");
    studentList.add("Lily");
    studentList.add("Samantha");
    studentList.add("Tony");

    // Replace elements at multiple positions in the ArrayList
    String replacedStudentOne = studentList.set(1, "David");
    String replacedStudentTwo = studentList.set(2, "George");

    // Print the updated ArrayList
    System.out.println("Updated ArrayList: " + studentList);
  }
}

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Here is the output:

Updated ArrayList: [John, David, George, Tony]

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Example 2: Using .set() with Integers

This example uses the .set() method to replace an integer with another integer in an ArrayList:

import java.util.ArrayList;

public class Example2 {
  public static void main(String[] args) {
    // Create an ArrayList
    ArrayList<Integer> numbers = new ArrayList<>();

    // Add values to the ArrayList
    numbers.add(10);
    numbers.add(20);
    numbers.add(30);

    // Replace the second element
    numbers.set(1, 99);

    // Print the updated ArrayList
    System.out.println(numbers);
  }
}

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Here is the output:

[10, 99, 30]

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Example 3: Handling Index Errors

This example attempts to replace an element at an out-of-bounds index using the .set() method, resulting in an IndexOutOfBoundsException:

import java.util.ArrayList;

public class Example3 {
  public static void main(String[] args) {
    // Create an ArrayList
    ArrayList<String> colors = new ArrayList<>();

    // Add values to the ArrayList
    colors.add("Red");
    colors.add("Green");

    try {
        colors.set(5, "Blue");
    } catch (IndexOutOfBoundsException e) {
        System.out.println("Error: " + e.getMessage());
    }
  }
}

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In this example, the try...catch block is used to catch the exception and display the error message.

Here is the output:

Error: Index 5 out of bounds for length 2

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Frequently Asked Questions

1. Can .set() be used to add new elements to a list?

No. The .set() method replaces an existing element at a given index. To insert a new element, use .add() instead.

2. Is .set() available for all collections in Java?

No. .set() is only available for classes that implement the List interface, such as ArrayList, LinkedList, and Vector.

3. Does .set() change the size of the list?

No. .set() only modifies the value at the specified index.