removeIf() Method in Java Collection With Examples

In this post we'll see how to use removeIf() method to remove elements from the Collection that satisfy the given condition. The removeIf() method is included in java.util.Collection interface in Java 8. Since it is part of Collection interface so you can use it with Collections like ArrayList, HashSet that implements Collection interface. To use it with HashMap you will have to get a collection view of the Map, since Map doesn't implement Collection interface.

Table of contents

1. Java removeIf() method syntax
2. Removing elements from ArrayList using removeIf() method
3. Removing elements from HashSet using removeIf() method
4. Removing elements from HashMap using removeIf() method

Java removeIf() method syntax

boolean removeIf(Predicate<? super E> filter)

Parameter passed to this method is of type Predicate functional interface, which can be implemented as a boolean-valued function with one argument.

Method returns true if any elements were removed.

Removing elements from ArrayList using removeIf() method

In this example we'll have a list of cities and we'll remove elements from this ArrayList using removeIf() method. In passed Predicate if the condition holds true for any of the elements, then that element is removed from the list.

import java.util.ArrayList;
import java.util.List;

public class RemoveIf {

  public static void main(String[] args) {
    List<String> cityList = new ArrayList<String>();
    cityList.add("Delhi");
    cityList.add("Mumbai");
    cityList.add("Kolkata");
    cityList.add("Hyderabad");
    cityList.add("Bangalore");
    cityList.add("Mumbai");
    System.out.println("*** List Initially ***");
    System.out.println(cityList);
    cityList.removeIf(p -> p.equalsIgnoreCase("Hyderabad") || 
          p.equalsIgnoreCase("Bangalore"));
    System.out.println("After Removal " + cityList);
  }
}

Output

*** List Initially ***
[Delhi, Mumbai, Kolkata, Hyderabad, Bangalore, Mumbai]
After Removal [Delhi, Mumbai, Kolkata, Mumbai]

Removing elements from HashSet using removeIf() method

You can use removeIf() method with HashSet also to remove elements from the Set based on the passed condition. In the given example condition is to remove cities having name of length more than 6.

import java.util.HashSet;
import java.util.Set;

public class RemoveIf {

  public static void main(String[] args) {
    // creating a HashSet
    Set<String> citySet = new HashSet<String>();
    // Adding elements
    citySet.add("London");        
    citySet.add("Tokyo");
    citySet.add("New Delhi");
    citySet.add("Beijing");
    citySet.add("Nairobi");
    System.out.println("*** Set Initially ***");
    System.out.println(citySet);
    
    // Remove all cities having length more than 6
    citySet.removeIf(e -> e.length() > 6);
    System.out.println("After Removal " + citySet);
  }
}

Output

*** Set Initially ***
[Beijing, New Delhi, Nairobi, Tokyo, London]
After Removal [Tokyo, London]

Removing elements from HashMap using removeIf() method

To use removeIf() method with a Map you have to get Collection view of a Map. After getting the Collection view of a Map removeIf() method can be used.

import java.util.HashMap;
import java.util.Map;


public class RemoveIf {

  public static void main(String[] args) {
    Map<String, String> cityMap = new HashMap<String, String>();
    // Adding elements
    cityMap.put("1","New York City" );
    cityMap.put("2", "New Delhi");
    cityMap.put("3", "Mumbai");
    cityMap.put("4", "Beijing");
    cityMap.put("5", "Berlin");

    System.out.println("*** Map Initially ***");
    System.out.println(cityMap);
      
    // Use entrySet to get Set view of all Map entries. 
    // Remove entry from Map based on the condition for value.
    cityMap.entrySet().removeIf(entry -> entry.getValue().equals("Beijing"));
    System.out.println("*** Map After removal ***");
    System.out.println(cityMap);
  }
}

Output

*** Map Initially ***
{1=New York City, 2=New Delhi, 3=Mumbai, 4=Beijing, 5=Berlin}
*** Map After removal ***
{1=New York City, 2=New Delhi, 3=Mumbai, 5=Berlin}

That's all for this topic removeIf() Method in Java Collection With Examples. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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Related Topics

1. How to Remove Entry From HashMap in Java
2. How to Remove Elements From an ArrayList in Java
3. How to Remove Duplicate Elements From an ArrayList in Java
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