Collections.replaceAll() method and List.replaceAll() method in Java

The replaceAll() method of Collections interface accepts a List object, two typed parameters representing old and new values, replaces the old values with the new values in the list.

Example

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class ReplaceAllExample {
   public static void main(String args[]) {
      List<String> list = new ArrayList<String>();
      list.add("Java");
      list.add("Java Script");
      list.add("HBase");
      list.add("CoffeeScript");
      list.add("TypeScript");
      System.out.println("Contents of list: "+list);
      Collections.replaceAll(list, "Java", "JAVA");
      System.out.print("Contents of list after replace operation: \n"+list);
   }
}

Output

Contents of list: [Java, Java Script, HBase, CoffeeScript, TypeScript]
Contents of list after replace operation:
[JAVA, Java Script, HBase, CoffeeScript, TypeScript]

The replaceAll() method of the List interface accept an object of the UnaryOperator representing a particular operation performs the specified operation on all the elements of the current list and replaces the existing values with the resultant values.

Example

import java.util.ArrayList;
import java.util.function.UnaryOperator;
class Op implements UnaryOperator<String> {
   public String apply(String str) {
      return str.toUpperCase();
   }
}
public class Test {
   public static void main(String[] args) throws CloneNotSupportedException {
      ArrayList<String> list = new ArrayList<>();
      list.add("Java");
      list.add("JavaScript");
      list.add("CoffeeScript");
      list.add("HBase");
      list.add("OpenNLP");
      System.out.println("Contents of the list: "+list);
      list.replaceAll(new Op());
      System.out.println("Contents of the list after replace operation: \n"+list);
   }
}

Output

Contents of the list: [Java, JavaScript, CoffeeScript, HBase, OpenNLP]
Contents of the list after replace operation:
[JAVA, JAVASCRIPT, COFFEESCRIPT, HBASE, OPENNLP]