Java Program to Empty an ArrayList in Java

14 Dec, 2021
ArrayList class is a resizable array, present in ‘java.util package’. The difference between a built-in array and an ArrayList in Java, is that the size of an array cannot be modified (i.e. if you want to append/add or remove element(s) to/from an array, you have to create a new array. However, elements can be added/appended or removed from an ArrayList without the need to create a new array.
Approaches :
Using clear() method.Using removeAll() method.
Using clear() method.
Using removeAll() method.
Method 1: Using clear() method as the clear() method of ArrayList in Java is used to remove all the elements from an ArrayList. The ArrayList will be completely empty after this call returns.
Syntax: 
public void clear() ;
Parameters: clear function takes no parameter
Return Value: This method does not return any value.
Exception: NA
Example:
Java
// Java Program  to empty an ArrayList in Java // Illustrating clear functionimport java.util.ArrayList; public class GFG {     // Main driver method    public static void main(String[] arg)    {         // Create an empty array list        // with an initial capacity of 4        ArrayList<String> numbers            = new ArrayList<String>(4);         // Use add() method to add elements        // in numbers ArrayList        numbers.add("10");        numbers.add("20");        numbers.add("30");        numbers.add("40");         // Printing numbers ArrayList        System.out.println("Numbers ArrayList : "                           + numbers);         // Finding size of numbers ArrayList        int numbers_size = numbers.size();         // Display message        System.out.println("Numbers ArrayList consists of: "                           + numbers_size + " elements");         // Display Message to between changes made in        // ArrayList         // System.out.println("Performing clear operation by        // using clear function");         // Using clear function        numbers.clear();         int numbers_size_new = numbers.size();         // Printing new ArrayList        System.out.println(            "Finally Numbers ArrayList consists of: "            + numbers_size_new + " elements");    }}
Numbers ArrayList : [10, 20, 30, 40]
Numbers ArrayList consists of 4 elements
Performing clear operation by using clear function
Finally Numbers ArrayList consists of 0 elements
Method 2: Using removeAll() method as this method of ArrayList class is used to remove from this list all of its elements that are contained in the specified collection.
Syntax:
public boolean removeAll(Collection c) ;
Parameters: This method takes collection c as a parameter containing elements to be removed from this list.
Return Value: This method returns true if this list changed as a result of the call.
Exception/s: This method throws NullPointerException if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null.
Example:
Java
// Java Program  to empty an ArrayList in Java// Java code to illustrate removeAll function // Importing ArrayList libraryimport java.util.ArrayList; public class GFG {     // Main driver method    public static void main(String[] arg)    {         // Create an empty array list        // with an initial capacity of 4        ArrayList<String> numbers            = new ArrayList<String>(4);         // Using add() method to add elements in numbers        // ArrayList        numbers.add("10");        numbers.add("20");        numbers.add("30");        numbers.add("40");         // Printing numbers ArrayList        System.out.println("Numbers ArrayList : "                           + numbers);         // Finding size of numbers ArrayList        int numbers_size = numbers.size();         // Display message        System.out.println("Numbers ArrayList consists of "                           + numbers_size + " elements");         // Display Message        System.out.println(            "Performing clear operation by using clear function");         // Using removeAll function        numbers.removeAll(numbers);         // Displaying final ArrayList count of elements        int numbers_size_new = numbers.size();        System.out.println(            "Finally Numbers ArrayList consists of "            + numbers_size_new + " elements");    }}
Numbers ArrayList : [10, 20, 30, 40]
Numbers ArrayList consists of 4 elements
Performing clear operation by using clear function
Finally Numbers ArrayList consists of 0 elements
anikakapoor
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