This program generates an ArrayList having 100 elements. All but one
reference String objects with the value "XXX". One references "Waldo".
Your job is to fill-in the blanks to find the index of "Waldo",
replace that element with a reference to "XXX", and prove that "Waldo"
no longer exists. Do NOT modify any existing code.

import java.util.*;
public class Lab23C {
  public static void main(String[] args) {
    ArrayList names = new ArrayList();
    for (int i = 0, n = (int)(Math.random()*100); i < 100; i++) {
      if (i == n) {
        names.add("Waldo");
      }
      else {
        names.add("XXX");
      }
    }
    int index = _________________;    // Find the index of "Waldo"
    System.out.println("\"Waldo\" at index: " + index);
    ____________________;             // Replace the element with a
reference to "XXX"
    if (!_______________________) {   // Prove that "Waldo" no longer exists
      System.out.println("Waldo is gone");
    }
  }
} 

      When successful, the program should display output similar to
the following (the index will vary):

 

     "Waldo" at index: 43
  Waldo is gone

Here is the code:

import java.util.*;
public class Lab23C {
  public static void main(String[] args) {
    ArrayList names = new ArrayList();
    for (int i = 0, n = (int)(Math.random()*100); i < 100; i++) {
      if (i == n) {
        names.add("Waldo");
      }
      else {
        names.add("XXX");
      }
    }
    int index = names.indexOf("Waldo");    // Find the index of "Waldo"
    System.out.println("\"Waldo\" at index: " + index);

    names.set(index, "XXX");             // Replace the element with a
reference to "XXX"

    if (!names.contains("Waldo")) {   // Prove that "Waldo" no longer exists
      System.out.println("Waldo is gone");
    }
  }
}