Java ArrayList ensureCapacity() Method
Java ArrayListThe ensureCapacity() method is used to set the dynamic array to have a specified capacity size.
The syntax of the ensureCapacity() method is:
arraylist.ensureCapacity(int minCapacity)
Note:arraylist is an object of the ArrayList class.
Parameter Description:
- minCapacity - the capacity of the dynamic array
Return Value
No return value.
Example
ArrayList sureCapacity() usage example:
Example
class Main {
public static void main(String[] args){
// Create a dynamic array
ArrayList<String> sites = new ArrayList<>();
// Set the capacity size of the arraylist
sites.ensureCapacity(3);
sites.add("Google");
sites.add("Example");
sites.add("Taobao");
System.out.println("Website list: " + sites);
}
}
Executing the above program produces the following output:
网站列表: [Google, Example, Taobao]
In the above example, we created an array named sites.
Note this line:
sites.ensureCapacity(3);
We use the ensureCapacity() method to adjust the size of the dynamic array to be able to store 3 elements.
An ArrayList in Java can dynamically adjust its size. That is, if we add more than 3 elements to the arraylist, it will automatically adjust its size, for example:
Example
class Main {
public static void main(String[] args){
// Create a dynamic array
ArrayList<String> sites = new ArrayList<>();
// Set the capacity size of the arraylist
sites.ensureCapacity(3);
sites.add("Google");
sites.add("Example");
sites.add("Taobao");
// Add the fourth element
sites.add("Wiki");
System.out.println("Website list: " + sites);
}
}
Executing the above program produces the following output:
网站列表: [Google, Example, Taobao, Wiki]
In the above example, we use the ensureCapacity() method to adjust the size of the dynamic array to store 3 elements. However, when we add a 4th element to the arraylist, the arraylist adjusts its size automatically.
Then, if the arraylist can automatically adjust its size, why do we still need to use the ensureCapacity() method to adjust the size of the arraylist?
This is because if we use the ensureCapacity() method to adjust the size of the arraylist, the arraylist will immediately adjust to the specified capacity. Otherwise, the size of the arraylist will be adjusted every time an element is added.
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