How to remove specific object from ArrayList in Java?

Question

How can I remove specific object from ArrayList? Suppose I have a class as below:

import java.util.ArrayList;    
public class ArrayTest {
    int i;

    public static void main(String args[]){
        ArrayList<ArrayTest> test=new ArrayList<ArrayTest>();
        ArrayTest obj;
        obj=new ArrayTest(1);
        test.add(obj);
        obj=new ArrayTest(2);
        test.add(obj);
        obj=new ArrayTest(3);
        test.add(obj);
    }
    public ArrayTest(int i){
        this.i=i;
    }
}

How can I remove object with new ArrayTest(1) from my ArrayList<ArrayList>

Answer 1

ArrayList removes objects based on the equals(Object obj) method. So you should implement properly this method. Something like:

public boolean equals(Object obj) {     if (obj == null) return false;     if (obj == this) return true;     if (!(obj instanceof ArrayTest)) return false;     ArrayTest o = (ArrayTest) obj;     return o.i == this.i; } 

Or

public boolean equals(Object obj) {     if (obj instanceof ArrayTest) {         ArrayTest o = (ArrayTest) obj;         return o.i == this.i;     }     return false; } 

Answer 2

If you are using Java 8 or above:

test.removeIf(t -> t.i == 1); 

Java 8 has a removeIf method in the collection interface. For the ArrayList, it has an advanced implementation (order of n).

Answer 3

In general an object can be removed in two ways from an ArrayList (or generally any List), by index (remove(int)) and by object (remove(Object)).

In this particular scenario: Add an equals(Object) method to your ArrayTest class. That will allow ArrayList.remove(Object) to identify the correct object.