Java ArrayList set() Usage and Example

Java ArrayList Methods

The Java ArrayList set() method replaces the element at the specified position with the specified element from the arraylist.

The syntax of set() method is:

arraylist.set(int index, E element)

set() parameters

The set() method has two parameters.

• index - Position of the replaced element

• element - New element to be stored at index
  

set() return value

• Returns the element previously at the index
  

NoteIf the specified index is out of range, the set() method will throw IndexOutOfBoundsException.

Example1Replace element in ArrayList

import java.util.ArrayList;
class Main {
　　public static void main(String[] args) {
　　　　//Create ArrayList
　　　　ArrayList<String> languages = new ArrayList<>();
　　　　//Add elements to ArrayList
　　　　languages.add("Python");
　　　　languages.add("English");
　　　　languages.add("JavaScript");
　　　　System.out.println("ArrayList: "　+　languages);
　　　　//replacement index1element at the position
　　　　String element = languages.set(1, "Java");
　　　　System.out.println("Updated ArrayList: ",　+　languages);
　　　　System.out.println("The replaced element: ",　+　element);
　　}
}

Output Result

ArrayList: [Python, English, JavaScript]
Updated ArrayList: [Python, Java, JavaScript]
element being replaced: English

In the above example, we created an ArrayList named languages. Here, we use the set() method to replace the index1(English) element to replace Java.

Note：If you are not sure of the index number of an element, you can useArrayList indexOf()methods.

ArrayList set() and add() methods

The syntax of add() and set() methods looks very similar.

//　add() syntax
arraylist.add(int index, E element)
//　set() syntax
arraylist.set(int index, E element)

And, both methods add a new element to the arraylist. This is why some people think these two methods are similar.

However, there are major differences between them.

• The set() method is used to: Add a new element at the specified position by replacing the old element at the specified position.
  

• The add() method is used to: Add a new element at the specified position by moving the old element to the correct position.
  

Example2Usage of ArrayList set() and add()

import java.util.ArrayList;
class Main {
　　public static void main(String[] args) {
　　　　//Create ArrayList
　　　　ArrayList<String> languages1　= new ArrayList<>();
　　　　//Add elements to ArrayList
　　　　languages1.add("Python");
　　　　languages1.add("English");
　　　　languages1.add("JavaScript");
　　　　//create another one like language1similar ArrayList
　　　　ArrayList<String> languages2　= new ArrayList<>();
　　　　//Set languages1add all elements in languages2in
　　　　languages2.addAll(languages1);
　　　　System.out.println("ArrayList: "　+　languages1);
　　　　//Using the set() method
　　　　languages1.set(1, "Java");
　　　　System.out.println("set() after the ArrayList: "　+　languages1);
　　　　//Using the add() method
　　　　languages2.add(1, "Java");
　　　　System.out.println("add() after the ArrayList: "　+　languages2);
　　}
}

Output Result

ArrayList: [Python, English, JavaScript]
ArrayList after set(): [Python, Java, JavaScript]
ArrayList after add(): [Python, Java, English, JavaScript]

In the above example, we created two arraylists named languages1and languages2of the ArrayList. We usedArrayList addAll()methods, so that the two arraylists have the same elements.

Here,

• The set() method replaces the element at the position1The 'English' element at the position

• The add() method moves the element 'English' to the position2

Can be accessedJava ArrayList add()to learn more information.

Java ArrayList Methods