Replacing All Occurrences of Specified Element of Java ArrayList - GeeksforGeeks

15 Nov, 2021
ArrayList is present in java.util package and it is the implementation class of List interface. It does allow the duplicates elements and also it maintains the insertion order of the elements. It dynamically resized its capacity. Though, it may be slower than standard arrays but can be helpful in programs where lots of manipulation in the array is needed.
Example: In this program, we will first create an ArrayList of Integers and add elements using add() method, Now we will iterate over the ArrayList elements using the for each loop.
Java
import java.io.*;import java.util.ArrayList;import java.util.Collections;class GFG {    public static void main(String[] args)    {        // ArrayList of Integers        ArrayList<Integer> gfg = new ArrayList<>();         // adding members into the list now        gfg.add(1);        gfg.add(20);        gfg.add(21);        gfg.add(13);        gfg.add(21);        gfg.add(10);        gfg.add(21);         // printing all the elements using for each loop        for (Integer value : gfg) {            System.out.println(value);        }    }}
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Approach(Using replaceAll() method)
In this program, we will create an ArrayList of Integers and add elements in it using add() method, then we will replace all occurrences of 21 with 200 using replaceAll() method.
Syntax:
public static  boolean replaceAll(List list, T oldVal, T newVal)
Parameters: This method takes the following argument as a Parameter
list: the list in which replacement is to occur.
oldVal: the old value to be replaced.
newVal: the new value with which oldVal is to be replaced.
Return Value: This method returns true if list contained one or more elements e such that (oldVal==null ? e==null : oldVal.equals(e)).
Example 1:
Java
// Java program for Replacing All Occurrences of Specified// Element of ArrayList import java.io.*;import java.util.ArrayList;import java.util.Collections; class GFG {    public static void main(String[] args)    {        // ArrayList of Integers        ArrayList<Integer> gfg = new ArrayList<>();         // adding members into the list now        gfg.add(1);        gfg.add(20);        gfg.add(21);        gfg.add(13);        gfg.add(21);        gfg.add(10);        gfg.add(21);         // replacing 21 with 100 using replaceAll() method        Collections.replaceAll(gfg, 21, 200);         // printing all the elements using for each loop        for (Integer value : gfg) {            System.out.println(value);        }    }}
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Example 2:
Java
// Java program to demonstrate// replaceAll() method for Integer value import java.util.*; public class GFG {    public static void main(String[] argv) throws Exception    {        // creating object of List<String>        List<String> list = new ArrayList<String>();         // populate the vector        list.add("?");        list.add("For");        list.add("?");         // printing the vector        System.out.println("Initial values are :" + list);         // replacing value        // using replaceAll() method        Collections.replaceAll(list, "?", "Geeks");         System.out.println("Value after replace :" + list);    }}
Initial values are :[?, For, ?]
Value after replace :[Geeks, For, Geeks]
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