Remove all elements from the ArrayList in Java
Prerequisite: ArrayList in Java
Given an ArrayList, the task is to remove all elements of the ArrayList in Java.
Examples:
Input: ArrayList = [1, 2, 3, 4]
Output: ArrayList = []
Input: ArrayList = [12, 23, 34, 45, 57, 67, 89]
Output: ArrayList = []
- Using clear() method:
Syntax:
collection_name.clear();
Code of clear() method:
public void clear() {
for (int i = 0; i < size; i++)
list[i] = null;
size = 0;
}
Below is the implementation of the above approach:
import java.util.ArrayList;
public class GFG {
public static void main(String[] args)
{
ArrayList<String> list = new ArrayList<>();
list.add( "Geeks" );
list.add( "for" );
list.add( "Geeks" );
list.add( "Gaurav" );
System.out.println( "ArrayList: " + list);
System.out.println( "Size of ArrayList = "
+ list.size());
list.clear();
System.out.println( "\nAfter clear\n\n"
+ "ArrayList: " + list);
System.out.println( "Size of ArrayList = "
+ list.size());
}
}
|
Output:
ArrayList: [Geeks, for, Geeks, Gaurav]
Size of ArrayList = 4
After clear
ArrayList: []
Size of ArrayList = 0
Time Complexity: O(N)
- Using removeAll() method
Syntax:
collection_name.removeAll(collection_name);
Code of removeAll() method:
public boolean removeAll(Collection list) {
boolean isModi = false;
Iterator ite= iterator();
while (ite.hasNext()) {
if (list.contains(ite.next())) {
ite.remove();
isModi = true;
}
}
return isModi;
}
Below is the implementation of the above approach:
import java.util.ArrayList;
public class GFG {
public static void main(String[] args)
{
ArrayList<String> list = new ArrayList<>();
list.add( "Geeks" );
list.add( "for" );
list.add( "Geeks" );
list.add( "Gaurav" );
System.out.println( "ArrayList: " + list);
System.out.println( "Size of ArrayList = "
+ list.size());
list.removeAll(list);
System.out.println( "\nAfter clear\n\n"
+ "ArrayList: " + list);
System.out.println( "Size of ArrayList = "
+ list.size());
}
}
|
Output:
ArrayList: [Geeks, for, Geeks, Gaurav]
Size of ArrayList = 4
After clear
ArrayList: []
Size of ArrayList = 0
Time Complexity: O(N^2)
Last Updated :
11 Dec, 2018
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