- Given an arraylist collection of String objects in java.
- We would like to retain certain elements of arraylist (and would like to remove rest of elements of arraylist).
- Arraylist has following method to retain elements.
- boolean retainAll(Collection<?> c)
- Retains only the elements in this list that are contained in the specified collection.
- We will create array list containing number of sports.
- OrignalArrayList:[archery, badminton, canoe, boxing, diving, beach volleyball]
- We would like to retain elements in original array list, which are present in retainSportsList.
- e.g. retainSportsList: [soccer, judo, archery, badminton]
- The output of OrignalArrayList.retainAll(retainSportsList) should return [archery, badminton]
- i.e. All elements of retainSportsList will be retained in OrignalArrayList (if present in OriginalArrayList).
1. Retain/remove String objects/elements of arraylist collection in java
package org.learn.collection.list.arrayList;
import java.util.ArrayList;
public class DemoRetainInOfArrayList {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<>();
arrayList.add("archery");
arrayList.add("badminton");
arrayList.add("canoe");
arrayList.add("boxing");
arrayList.add("diving");
arrayList.add("beach volleyball");
System.out.println("Demo of retain method: ");
demoRetainAll(arrayList);
}
private static void demoRetainAll(ArrayList<String> arrayList) {
System.out.println("1. Orignal ArrayList:" + arrayList);
ArrayList<String> retainSportsList = new ArrayList<>();
retainSportsList.add("soccer");
retainSportsList.add("judo");
retainSportsList.add("archery");
retainSportsList.add("badminton");
System.out.println("2. Elements in retainSportsList:"+retainSportsList);
arrayList.retainAll(retainSportsList);
//What ever element presents in source list, will be retained.
System.out.println("3. Retained elements in arraylist: " + arrayList);
}
}
2. Retain/remove String objects/elements of arraylist collection (example)
Demo of retain method:
1. Orignal ArrayList:[archery, badminton, canoe, boxing, diving, beach volleyball]
2. Elements in retainSportsList:[soccer, judo, archery, badminton]
3. Retained elements in arraylist: [archery, badminton]