CopyOnWriteArrayList indexOf() method in Java

The indexOf(Object o) method of CopyOnWriteArrayList returns the first occurrence of the element passed in the list. It returns -1 if the element is not present in the list. 

Syntax: 

public int indexOf(Object o)

Parameters: The function accepts a parameter o whose first occurrence is to be returned. 

Return Value: The function returns the first occurrence of the element. It returns -1 if the element is not present in the list. 

Below programs illustrate the above function: 

Program 1:

Java

// Java Program to illustrate the CopyOnWriteArrayList
// indexOf() method in Java
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.*;

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

        // create object of CopyOnWriteArrayList
        CopyOnWriteArrayList<Integer> ArrLis
            = new CopyOnWriteArrayList<Integer>();

        // Add elements
        ArrLis.add(32);
        ArrLis.add(67);
        ArrLis.add(67);
        ArrLis.add(100);

        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: " + ArrLis);

        // first occurrence of 67
        System.out.println("indexOf value: " + ArrLis.indexOf(67));
    }
}

Output:

CopyOnWriteArrayList: [32, 67, 67, 100]
indexOf value: 1

Program 2: 

Java

// Java Program to illustrate the CopyOnWriteArrayList
// indexOf() method in Java
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.*;

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

        // create object of CopyOnWriteArrayList
        CopyOnWriteArrayList<Integer> ArrLis
            = new CopyOnWriteArrayList<Integer>();

        // Add elements
        ArrLis.add(32);
        ArrLis.add(67);
        ArrLis.add(67);
        ArrLis.add(100);

        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: "
                                         + ArrLis);

        // 200 is not present
        System.out.println("indexOf value: "
                         + ArrLis.indexOf(200));
    }
}

Output:

CopyOnWriteArrayList: [32, 67, 67, 100]
indexOf value: -1

The indexOf(E e, int index) method of CopyOnWriteArrayList returns the first occurrence of the element passed in the list after position index. It returns -1 if the element is not present in the list. 

Syntax: 

public int indexOf(E e, int index)

• Parameters: The function accepts two parameters which are described below:
  • index: specifies the index from which the occurrence is to be searched.
  • e: specifies the element whose first occurrence from position index is to be returned.

Return Value: The function returns the first occurrence of the element after position index. It returns -1 if the element is not present in the list.

Exceptions: The function throws an IndexOutOfBoundsException if the specified index is negative.

Below programs illustrate the above function:

Program 1:

Java

// Java Program to illustrate the CopyOnWriteArrayList
// indexOf() method in Java
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.*;

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

        // create object of CopyOnWriteArrayList
        CopyOnWriteArrayList<Integer> ArrLis
            = new CopyOnWriteArrayList<Integer>();

        // Add elements
        ArrLis.add(32);
        ArrLis.add(67);
        ArrLis.add(67);
        ArrLis.add(67);

        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: "
                                        + ArrLis);

        // first occurrence of 67 from 2nd index
        System.out.println("indexOf value: "
                        + ArrLis.indexOf(67, 2));
    }
}

Output:

CopyOnWriteArrayList: [32, 67, 67, 67]
indexOf value: 2

Program 2:

Java

// Java Program to illustrate the CopyOnWriteArrayList
// indexOf() method in Java
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.*;

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

        // create object of CopyOnWriteArrayList
        CopyOnWriteArrayList<Integer> ArrLis
            = new CopyOnWriteArrayList<Integer>();

        // Add elements
        ArrLis.add(32);
        ArrLis.add(67);
        ArrLis.add(67);
        ArrLis.add(100);

        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: "
                                        + ArrLis);

        // -1 is out of range, hence exception
        System.out.println("indexOf value: "
                    + ArrLis.indexOf(-1, 200));
    }
}

Output:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1
    at java.util.concurrent.CopyOnWriteArrayList.indexOf(CopyOnWriteArrayList.java:198)
    at java.util.concurrent.CopyOnWriteArrayList.indexOf(CopyOnWriteArrayList.java:263)
    at GFG.main(GFG.java:24)