Vector indexOf() Method in Java

The java.util.vector.indexOf(Object element) method is used to check and find the occurrence of a particular element in the vector. If the element is present then the index of the first occurrence of the element is returned otherwise -1 is returned if the vector does not contain the element.

Syntax:

Vector.indexOf(Object element)

Parameters: This method accepts a mandatory parameter element of the type of Vector. It specifies the element whose occurrence is needed to be checked in the Vector.



Return Value: This method returns the index or position of the first occurrence of the element in the vector. Else it returns -1 if the element is not present in the vector. The returned value is of integer type.

Below programs illustrate the Java.util.Vector.indexOf() method:

Program 1:

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// Java code to illustrate indexOf()
import java.util.*;
  
public class VectorDemo {
    public static void main(String args[])
    {
  
        // Creating an empty Vector
        Vector<String> vec_tor = new Vector<String>();
  
        // Use add() method to add elements in the Vector
        vec_tor.add("Geeks");
        vec_tor.add("for");
        vec_tor.add("Geeks");
        vec_tor.add("10");
        vec_tor.add("20");
  
        // Displaying the Vector
        System.out.println("Vector: " + vec_tor);
  
        // The first position of an element
        // is returned
        System.out.println("The first occurrence of Geeks is at index:"
                           + vec_tor.indexOf("Geeks"));
        System.out.println("The first occurrence of 10 is at index: "
                           + vec_tor.indexOf("10"));
    }
}

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Output:

Vector: [Geeks, for, Geeks, 10, 20]
The first occurrence of Geeks is at index:0
The first occurrence of 10 is at index: 3

Program 2:

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// Java code to illustrate indexOf()
import java.util.*;
  
public class VectorDemo {
    public static void main(String args[])
    {
  
        // Creating an empty Vector
        Vector<Integer> vec_tor = new Vector<Integer>();
  
        // Use add() method to add elements in the Vector
        vec_tor.add(1);
        vec_tor.add(2);
        vec_tor.add(3);
        vec_tor.add(10);
        vec_tor.add(20);
  
        // Displaying the Vector
        System.out.println("Vector: " + vec_tor);
  
        // The first position of an element
        // is returned
        System.out.println("The first occurrence of Geeks is at index:"
                           + vec_tor.indexOf(2));
        System.out.println("The first occurrence of 10 is at index: "
                           + vec_tor.indexOf(20));
    }
}

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Output:

Vector: [1, 2, 3, 10, 20]
The first occurrence of Geeks is at index:1
The first occurrence of 10 is at index: 4


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