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Stack indexOf(Object, int) method in Java with Example
  • Last Updated : 24 Dec, 2018

The Java.util.Stack.indexOf(Object element, int index) method is used to the index of the first occurrence of the specified element in this Stack, searching forwards from index, or returns -1 if the element is not found. More formally, returns the lowest index i such that (i >= index && Objects.equals(o, get(i))), or -1 if there is no such index.

Syntax:

public int indexOf(Object element, 
                        int index)

Parameters: This method accepts two parameters:

  • element of the type of Stack. It specifies the element whose occurrence is needed to be checked in the Stack.
  • index of the type Integer. It specifies the index to start searching from

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

Exception: This method throws IndexOutOfBoundsException if the specified index is negative.



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

Program 1:

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

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Output:

Stack: [Geeks, for, Geeks, 10, Geeks]
The first occurrence of Geeks is at index:0
The second occurrence of Geeks is at index: 0

Program 2: To demonstrate IndexOutOfBoundsException

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// Java code to illustrate indexOf()
import java.util.*;
  
public class StackDemo {
    public static void main(String args[])
    {
  
        // Creating an empty Stack
        Stack<Integer> stack = new Stack<Integer>();
  
        // Use add() method to add elements in the Stack
        stack.add(1);
        stack.add(2);
        stack.add(3);
        stack.add(10);
        stack.add(20);
  
        // Displaying the Stack
        System.out.println("Stack: " + stack);
  
        // Get the -1 occurrence of Geeks
        // using indexOf() method
        System.out.println("The -1 occurrence"
                           + " of Geeks is at index: ");
  
        try {
            stack.indexOf("Geeks",
                          stack.indexOf("Geeks"));
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

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Output:

Stack: [1, 2, 3, 10, 20]
The -1 occurrence of Geeks is at index: 
java.lang.ArrayIndexOutOfBoundsException: -1

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