Question

complete this code for me, this is java question.

// Some comments omitted for brevity

import java.util.*;

/*
* A class to demonstrate an ArrayList of Player objects
*/
public class ListOfPlayers
{
// an ArrayList of Player objects
private ArrayList players;

public ListOfPlayers()
{
// creates an empty ArrayList of Players
players = new ArrayList<>();
}

public void add3Players()
{
// adds 3 Player objects
players.add(new Player("David", 10));
players.add(new Player("Susan", 5));
players.add(new Player("Jack", 25));
}
  
public void displayPlayers()
{
// asks each Player object to display its contents
// - what if the list is empty?
for (Player currentPlayer : players)
currentPlayer.display();
}
  
// Q.4(a) for Week 8
public void clearPlayers()
{
/* Add code to clear all the Player objects from the ArrayList
* (ie. the list will be emptied after the operation)
*
* Hints:
* - display the list before AND after the operation to check
* if it was performed correctly
*/
  
// wrote your code here...
players.clear();
}

// Q.4(b) for Week 8
public void addPlayer()
{
/* Add code to ask user to input a name and a position,
* then use the data to add a new Player object into the
* players attribute.
*
* There is no need for any input validations.
*
* Hints:
* - use a Scanner to get user inputs
* - create a new Player object
* - use the add() method of the ArrayList class to add it into the list
*/
  
// wrote your code here...
}

// Q.4(c) for Week 8
public int findPlayer(String name)
{
int index = -1;
  
/* Add code to allow user to search for an existing Player object
* in players. The parameter is a string representing the name
* of the Player object to search. The return value is the index
* where the object is found, or -1 if the object is not found.
*
* Assume there are no duplate names in the list.
*
* Hints:
* - use a loop to search through the ArrayList
* - compare the given name to each Player's name in the list
* - use the indexOf() method to return the required index
*/
  
// wrote your code here...
  
return index;
}

// Q.4(d) for Week 8
public boolean updatePlayerName(int index)
{
boolean success = false;
  
/* Add code to allow user to modify an existing Player object
* in players. The parameter is the index to the Player object
* in the ArrayList. Your code should first check if the given
* index is within the correct range (between 0-max, where max
* if the ize of the list. If the index is not valid,
* or the player list is empty,
* print out an error message, otherwise ask the user to input
* a new name and update the Player object with that name.
* If the update operation is successful, return true (otherwise
* return false).
*
* Hints:
* - check if index is valid and list is not empty
* - if yes, use it to get at the correct Player in the list
* - update the Player's name
* - return the appropriate boolean result
*/

// wrote your code here...
  
return success;
}
  
// *** Pre-tute Task 1 for Week 9 ***
public boolean removePlayer(String name)
{
boolean success = false;
  
/* Add code to allow user to remove an existing Player object
* in players. The parameter is the name of the Player object
* to be removed. Your code should first check if th object
* with that name does exist.
*
* Your code *MUST* make a call to the findPlayer() method you
* wrote in Q.4(c) above.
*
* If the remove operation is successful, return true (otherwise
* return false, and print a simple error message).
*
* Hints:
* - use the findPlayer() method to find the position of the object
* - remove the Player if it exists
* - return the appropriate boolean result
*/
  
// wrote your code here...
  
return success;
}
  
// *** Pre-tute Task 2 for Week 9 ***
public boolean updatePlayerName(String oldName, String newName)
{
boolean success = false;
  
/* Add code to allow user to modify an existing Player object
* in players. This time the method takes 2 parameters: oldName
* is the name for an Player object to be searched for, newName
* is the name to update the object with. Your code should first
* check if the object with the oldName does exist.
*
* Your code *MUST* make a call to the findPlayer() method you
* wrote in Q.4(c) above.
*
* If the update operation is successful, return true (otherwise
* return false, and print a simple error message).
*
* Hints:
* - use the findPlayer() method to find the position of the object
* - update the Player's name with the given parameter (newName)
* - return the appropriate boolean result
*/
  
// wrote your code here...

return success;
}
}

Answer 1

ListOfPlayers.java

import java.util.ArrayList;
import java.util.Scanner;

public class ListOfPlayers {
   //I changed from a generic ArrayList to parameterized ArrayList
   //Otherwise the for-each loop will give error in displayPlayers method
  
   private ArrayList<Player> players;

   public ListOfPlayers()
   {
       // creates an empty ArrayList of Players
       players = new ArrayList<Player>();
   }

   public void add3Players()
   {
       // adds 3 Player objects
       players.add(new Player("David", 10));
       players.add(new Player("Susan", 5));
       players.add(new Player("Jack", 25));
   }
  
   public void displayPlayers()
   {
       // asks each Player object to display its contents
       // - what if the list is empty?
       for (Player currentPlayer : players)
           currentPlayer.display();
      
       //For loop is inherently safe against empty, if the list is empty,
       //It never executes.
   }
  
   // Q.4(a) for Week 8
   public void clearPlayers()
   {
       /* Add code to clear all the Player objects from the ArrayList
       * (ie. the list will be emptied after the operation)
       *
       * Hints:
       * - display the list before AND after the operation to check
       * if it was performed correctly
       */
       //Display old players
       this.displayPlayers();
       players.clear();
       this.displayPlayers();
   }

   // Q.4(b) for Week 8
   public void addPlayer()
   {
   /* Add code to ask user to input a name and a position,
   * then use the data to add a new Player object into the
   * players attribute.
   *
   * There is no need for any input validations.
   *
   * Hints:
   * - use a Scanner to get user inputs
   * - create a new Player object
   * - use the add() method of the ArrayList class to add it into the list
   */
  
       Scanner scan = new Scanner(System.in);
       System.out.println("Adding player.....");
       System.out.println("Enter name: ");
       String name = scan.nextLine();
       System.out.println("Enter position: ");
       int position = scan.nextInt();
       Player p = new Player(name, position);
       players.add(p);
   }

   // Q.4(c) for Week 8
   public int findPlayer(String name)
   {
   int index = -1;
  
   /* Add code to allow user to search for an existing Player object
   * in players. The parameter is a string representing the name
   * of the Player object to search. The return value is the index
   * where the object is found, or -1 if the object is not found.
   *
   * Assume there are no duplate names in the list.
   *
   * Hints:
   * - use a loop to search through the ArrayList
   * - compare the given name to each Player's name in the list
   * - use the indexOf() method to return the required index
   */
       for(Player p: players) {
           if(p.name.contentEquals(name))
               index = players.indexOf(p);
       }
      
       return index;
   }

   // Q.4(d) for Week 8
   public boolean updatePlayerName(int index)
   {
   boolean success = false;
  
   /* Add code to allow user to modify an existing Player object
   * in players. The parameter is the index to the Player object
   * in the ArrayList. Your code should first check if the given
   * index is within the correct range (between 0-max, where max
   * if the ize of the list. If the index is not valid,
   * or the player list is empty,
   * print out an error message, otherwise ask the user to input
   * a new name and update the Player object with that name.
   * If the update operation is successful, return true (otherwise
   * return false).
   *
   * Hints:
   * - check if index is valid and list is not empty
   * - if yes, use it to get at the correct Player in the list
   * - update the Player's name
   * - return the appropriate boolean result
   */
       //If valid index
       if(index>=0 && index<players.size()) {
           System.out.println("Updating player name at index " + index);
           Scanner scan = new Scanner(System.in);
           System.out.println("Enter name: ");
           String name = scan.nextLine();
           //Create new player with new name and old position
           Player p = new Player(name, players.get(index).position);
           //Remove old object at the specified index
           players.remove(index);
           //Add updated player at the index
           players.add(index, p);
           success = true;
       } else {
           System.out.println("Error updating player name. ");
       }
  
       return success;
   }
  
   // *** Pre-tute Task 1 for Week 9 ***
   public boolean removePlayer(String name)
   {
   boolean success = false;
  
   /* Add code to allow user to remove an existing Player object
   * in players. The parameter is the name of the Player object
   * to be removed. Your code should first check if th object
   * with that name does exist.
   *
   * Your code *MUST* make a call to the findPlayer() method you
   * wrote in Q.4(c) above.
   *
   * If the remove operation is successful, return true (otherwise

   * Hints:
   * - use the findPlayer() method to find the position of the object
   * - remove the Player if it exists
   * - return the appropriate boolean result
   */
  
       int index = findPlayer(name);
       //If object found in players list
       if(index>0) {
           players.remove(index);
           success = true;
       }
  
   return success;
   }
  
   // *** Pre-tute Task 2 for Week 9 ***
   public boolean updatePlayerName(String oldName, String newName)
   {
   boolean success = false;
  
   /* Add code to allow user to modify an existing Player object
   * in players. This time the method takes 2 parameters: oldName
   * is the name for an Player object to be searched for, newName
   * is the name to update the object with. Your code should first
   * check if the object with the oldName does exist.
   *
   * Your code *MUST* make a call to the findPlayer() method you
   * wrote in Q.4(c) above.
   *
   * If the update operation is successful, return true (otherwise
   * return false, and print a simple error message).
   *
   * Hints:
   * - use the findPlayer() method to find the position of the object
   * - update the Player's name with the given parameter (newName)
   * - return the appropriate boolean result
   */
  
       int index = findPlayer(oldName);
       if(index>=0) {
           //Create new player with new name
           Player p = new Player(newName, players.get(index).position);
           //Remove old player
           players.remove(index);
           //Add new player at that index
           players.add(index, p);
           success = true;
       }else
           System.out.println("Error updating old player name with new name.");
       return success;
   }
   //Test of above methods
   public static void main(String[] args) {
       ListOfPlayers lop = new ListOfPlayers();
       lop.add3Players();
       lop.displayPlayers();
       lop.addPlayer();
       lop.clearPlayers();
       lop.add3Players();
       lop.updatePlayerName(0);
       lop.displayPlayers();
       lop.removePlayer("Robert");
       lop.updatePlayerName("Robert", "David");
   }
}

Player.java

public class Player {
   String name;
   int position;
   Player(String s, int r){
       name = s;
       position = r;
   }
   public void display() {
       System.out.println("Name: " + name + " Position: " + position);
   }
}

I've addes some simple statements in main method to test. You can add more statements in main to test and understand, although I've included everything in comments.