size (); java arraylist

stackoverflow.com › questions › 8896758 › initial-size-for-the-arraylist

You're confusing the size of the array list with its capacity:

the size is the number of elements in the list;
the capacity is how many elements the list can potentially accommodate without reallocating its internal structures.

When you call new ArrayList<Integer>(10), you are setting the list's initial capacity, not its size. In other words, when constructed in this manner, the array list starts its life empty.

One way to add ten elements to the array list is by using a loop:

for (int i = 0; i < 10; i++) {
  arr.add(0);
}

Having done this, you can now modify elements at indices 0..9.

Answer from NPE on Stack Overflow

GeeksforGeeks

geeksforgeeks.org › java › arraylist-size-method-in-java-with-examples

ArrayList size() Method in Java with Examples - GeeksforGeeks

July 11, 2025 - Example 2: Here, we use the size() method to get the number of elements in an ArrayList of strings. ... // Java program to demonstrate the use of // size() method for String ArrayList import java.util.ArrayList; public class GFG { public static void main(String[] args) { // Creating an ArrayList of Strings ArrayList<String> f = new ArrayList<>(); // Adding elements to the ArrayList f.add("Apple"); f.add("Banana"); f.add("Orange"); // Getting and printing the // size of the ArrayList int s = f.size(); System.out.println("" + s); } }

Stack Overflow

stackoverflow.com › questions › 8896758 › initial-size-for-the-arraylist

java - Initial size for the ArrayList - Stack Overflow

Top answer

1 of 16

515

You're confusing the size of the array list with its capacity:

the size is the number of elements in the list;
the capacity is how many elements the list can potentially accommodate without reallocating its internal structures.

When you call new ArrayList<Integer>(10), you are setting the list's initial capacity, not its size. In other words, when constructed in this manner, the array list starts its life empty.

One way to add ten elements to the array list is by using a loop:

for (int i = 0; i < 10; i++) {
  arr.add(0);
}

Having done this, you can now modify elements at indices 0..9.

2 of 16

168

If you want a list with a predefined size you can also use:

List<Integer> arr = Arrays.asList(new Integer[10]);

Discussions

how to set a maximum size for ArrayList?

Use an if statement and the size() of the ArrayList. More on forum.processing.org

forum.processing.org

May 20, 2013

ArrayList default initialization size

Because index 5 is out of range. The starting size of 10 means that the array under the hood has a size of 10. Thats just so that it doesnt need to be resized immediately. It does not mean that you can add something to those later indexes. Think about it, by your logic an empty list would return a size of 10. More on reddit.com

r/javahelp

November 23, 2022

[JAVA] Why is my ArrayList size always 0

Your ArrayList contains 0 elements, so the size is 0. Your top is also initially -1, so the expression top == stack.size() - 1 will evaluate to -1 == 0 - 1, which is always true (until something is added to the stack). You may be confusing size (number of elements in the current ArrayList) with the capacity (maximum number of elements allowed in the current ArrayList). In any case, if you're trying to write a stack for learning purposes, you'd probably get more out of it if you implemented it on a more basic level, and used an array internally instead of an ArrayList which basically has already implemented most of the logic for you. Alternatively, if you just need a stack, you should probably use java.util.Stack instead of re-implementing one. More on reddit.com

r/learnprogramming

February 26, 2017

[Java] How to write .size() method for an ArrayList?

Look ar ArrayList's implementation, create your own class, and implement the most useful methods(add,get,remove,size). It should be pretty straightforward. As you'll see, there is a private variable size, that increases and decreases when you add/remove an object. More on reddit.com

r/learnprogramming

April 30, 2013

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