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Difference between ArrayList.clear() and ArrayList.removeAll() in java?
The ArrayList class in Java is a Resizable-array implementation of the List interface. It allows null values.
The clear() method this class removes all the elements from the current List object.
Example
import java.util.ArrayList; public class ClearExample { public static void main(String[] args){ //Instantiating an ArrayList object ArrayList<String> list = new ArrayList<String>(); list.add("JavaFX"); list.add("Java"); list.add("WebGL"); list.add("OpenCV"); list.add("Impala"); System.out.println("Contents of the Array List: \n"+list); //Removing the sub list list.clear(); System.out.println("Contents of the ArrayList object after invoking the clear() method: "+list); } }
Output
Contents of the Array List: [JavaFX, Java, WebGL, OpenCV, Impala] Contents of the ArrayList object after invoking the clear() method: []
Whereas, the removeAll() method of the ArrayList class accepts another collection object as a parameter and removes all the contents of it from the current ArrayList.
Example
import java.util.ArrayList; public class ClearExample { public static void main(String[] args){ //Instantiating an ArrayList object ArrayList<String> list1 = new ArrayList<String>(); list1.add("JavaFX"); list1.add("Java"); list1.add("WebGL"); list1.add("OpenCV"); list1.add("OpenNLP"); list1.add("JOGL"); list1.add("Hadoop"); list1.add("HBase"); list1.add("Flume"); list1.add("Mahout"); list1.add("Impala"); System.out.println("Contents of the Array List1 : \n"+list1); ArrayList<String> list2 = new ArrayList<String>(); list2.add("JOGL"); list2.add("Hadoop"); list2.add("HBase"); list2.add("Flume"); list2.add("Mahout"); list2.add("Impala"); System.out.println("Contents of the Array List1 : \n"+list2); //Removing elements list1.removeAll(list2); System.out.println("Contents of the Array List after removal: \n"+list1); } }
Output
Contents of the Array List1 : [JavaFX, Java, WebGL, OpenCV, OpenNLP, JOGL, Hadoop, HBase, Flume, Mahout, Impala] Contents of the Array List1 : [JOGL, Hadoop, HBase, Flume, Mahout, Impala] Contents of the Array List after removal: [JavaFX, Java, WebGL, OpenCV, OpenNLP]
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