Remove One Array From Another Array in Java

For removing one array from another array in java we will use the removeAll() method. This will remove all the elements of the array1 from array2 if we call removeAll() function from array2 and array1 as a parameter.

Syntax:

public boolean removeAll(Collection c)

Parameters: This method takes collection c as a parameter containing elements to be removed from this list.

Returns Value: This method returns true if this list changed as a result of the call.

Example 1:

Java

// Java program to Remove One Array From Another Array

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

class GFG {
    public static void main(String[] args)
    {

        // creating first array
        List<Integer> firstList = new ArrayList<>();

        // creating second array
        List<Integer> secondList = new ArrayList<>();

        // adding elements in first array
        firstList.add(100);
        firstList.add(200);
        firstList.add(300);
        firstList.add(400);
        firstList.add(500);
        firstList.add(600);

        // adding elements in second array
        secondList.add(300);
        secondList.add(500);

        // displaying element of first array
        System.out.println("elements in first array "
                           + firstList);

        // displaying element of second array
        System.out.println("elements in second array "
                           + secondList);

        // removing elements from firstarray
        firstList.removeAll(secondList);

        // displaying elements of first array
        // after removing elements of second array
        // from first array
        System.out.println("first array after removing second array from first array\n"
            + firstList);
    }
}

Output

elements in first array [100, 200, 300, 400, 500, 600]
elements in second array [300, 500]
first array after removing second array from first array
[100, 200, 400, 600]

Example 2:

In this example instead of using wrapper classes of java, we will use user-defined class but for using user-defined class we need to override equals() and hashCode() method.

Java

// Java program to Remove One Array From Another Array

import java.io.*;
import java.util.*;

class friendsDetail {

    // class field
    private String name;
    private String nickName;

    // parameterised constructor
    public friendsDetail(String name, String nickName)
    {
        this.name = name;
        this.nickName = nickName;
    }

    // getter for name
    public String getName() { return name; }

    // setter for name
    public void setName(String name) { this.name = name; }

    // getter for nickname
    public String getnickName() { return nickName; }

    // setter for nickname
    public void setNickName(int id)
    {
        this.nickName = nickName;
    }

    @Override public boolean equals(Object o)
    {

        if (this == o)
            return true;

        if (!(o instanceof friendsDetail))
            return false;

        friendsDetail that = (friendsDetail)o;

        return Objects.equals(getName(), that.getName())
            && Objects.equals(nickName, that.nickName);
    }

    @Override public int hashCode()
    {
        return Objects.hash(getName(), nickName);
    }

    // overriding toString method
    public String toString()
    {
        // return super.toString();
        return "(" + this.getName() + ":"
                        + this.getnickName() + ")";
    }
}
public class GFG {
    public static void main(String[] args)
    {
        ArrayList<friendsDetail> firstArrayList = new ArrayList<>();

        System.out.println("Our First ArrayList\n");

        // adding elements to first ArrayList
        firstArrayList.add(new friendsDetail("Amit", "Ghulla"));
        firstArrayList.add(new friendsDetail("Yashdeep", "Dopa"));
        firstArrayList.add(new friendsDetail("Jyoti", "Kauwa"));
        firstArrayList.add(new friendsDetail("Suraj", "Bhindi"));
        firstArrayList.add(new friendsDetail("Himanshu", "Lalten"));
        firstArrayList.add(new friendsDetail("Sarthak", "Nagin"));
        firstArrayList.add(new friendsDetail("Tsering", "Battak"));
        firstArrayList.add(new friendsDetail("Abhishek", "Liquid"));

        // Displaying output of first array using enhanced
        // for loop
        for (friendsDetail friend : firstArrayList) {
            System.out.println(friend);
        }

        ArrayList<friendsDetail> secondArrayList = new ArrayList<>();

        System.out.println("\nOur Second ArrayList\n");

        // adding elements to second ArrayList.
        secondArrayList.add(new friendsDetail("Amit", "Ghulla"));
        secondArrayList.add(new friendsDetail("Jyoti", "Kauwa"));
        secondArrayList.add(new friendsDetail("Himanshu", "Lalten"));
        secondArrayList.add(new friendsDetail("Abhishek", "Liquid"));

        // Displaying output of original array using
        // enhanced for loop
        for (friendsDetail friend : secondArrayList) {
            System.out.println(friend);
        }

        // removing second array elements from first array
        firstArrayList.removeAll(secondArrayList);

        System.out.println(
          "\nFirst array after removing second array from first array\n");

        // Displaying first array after removing second
        // array elements from first array
        for (friendsDetail friend : firstArrayList) {
            System.out.println(friend);
        }
    }
}

Output

Our First ArrayList

(Amit:Ghulla)
(Yashdeep:Dopa)
(Jyoti:Kauwa)
(Suraj:Bhindi)
(Himanshu:Lalten)
(Sarthak:Nagin)
(Tsering:Battak)
(Abhishek:Liquid)

Our Second ArrayList

(Amit:Ghulla)
(Jyoti:Kauwa)
(Himanshu:Lalten)
(Abhishek:Liquid)

First array after removing second array from first array

(Yashdeep:Dopa)
(Suraj:Bhindi)
(Sarthak:Nagin)
(Tsering:Battak)