Develop Reference

How to fix null error when I've already declared the variable

I am making a PVP RPG game and the display box comes out with "null" instead of the variable I have already declared.
I have declared the variable as the user's next input and stored that information in the variable. Then when I try to display the variable, it only shows "null",
System.out.println("Welcome, Player One and Player Two!");
delay(1500);
System.out.println("What is your name, Player One?");
playerOne.name = userInput.nextLine();
I already declared playerOne as a new character(different class)
System.out.println("Your turn, " + playerOne.name+".");
if (p1Swordgo == 1) {
This is the problem I'm coming up with. It is in the same main method and the variables are declared in the main method, and yes I imported scanner and declared the variable userInput
I expected it to be what the user typed in, but it came up with null. As I've said previous, it's in the same main method and nothing should go wrong, but it comes up with "null"
import java.util.Random;
import java.util.Scanner;
public class Arena {
Random generator = new Random();
public static void main(String[] args) {
Character playerOne = new Character(10,10,0);
Character playerTwo = new Character(10,10,0);
boolean P1hasClass = false;
boolean P2hasClass = false;
int p1Swordgo = 0;
int p2Alchgo = 0;
int p2Archgo = 0;
Scanner userInput = new Scanner(System.in);
System.out.println("Welcome, Player One and Player Two!");
delay(1500);
System.out.println("What is your name, Player One?");
playerOne.name = userInput.nextLine();
delay(1000);
System.out.println("Hello, " +playerOne.name +".");
delay(1000);
System.out.println("What is your name, Player Two?");
playerTwo.name = userInput.nextLine();
delay(1000);
System.out.println("Hello, " +playerTwo.name +".");
delay(1500);
countdown();
System.out.println("Your turn, " + playerOne.name+".");
if (p1Swordgo == 1) {
if (p2Archgo == 1 || p2Alchgo == 1) {
if (playerOne.move == 1){
System.out.println("What do you want to do?" +'\n' +"1 = Move into range of " +playerTwo.name +'\n' +"2 = Heal" +'\n' +"3 = Forfeit");
int P1Choice = userInput.nextInt();
if (P1Choice == 1) {
playerOne.move --;
System.out.println(playerOne.move);
}
}
}
}
}
public static void delay ( int time){
try {
Thread.sleep(time);
} catch (InterruptedException ex) {
Thread.currentThread().interrupt();
}
}
public static void countdown() {
delay(500);
System.out.println("Get ready to fight in 5,");
delay(1000);
System.out.println("4");
delay(1000);
System.out.println("3");
delay(1000);
System.out.println("2");
delay(1000);
System.out.println("1");
delay(1000);
System.out.println("Fight!");
delay(750);
}
}
And then in a class called Character
public class Character {
public int strength;
public double health;
public int move;
public String name;
public Character(double health, int strength, int move) {
this.health = health;
this.strength = strength;
this.name = name;
this.move = move;
}
}
And in a class called SwordFighter
public class SwordFighter extends Character {
public SwordFighter() {
super(60,15, 1);
}
}
And in a class called Archer
public class Archer extends Character{
public Archer() {
super(45,20, 0);
}
}
And finally, in a class called Alchemist
public class Alchemist extends Character {
public Alchemist() {
super(50,15, 0);
}
}
Thank you for your patience, by the way

Once the two players have chosen their name and you have set it using playerOne.name = userInput.nextLine();, you assign a different object, with a null name, to playerOne:
playerOne = new SwordFighter();
So, after this line has been executed, playerOne.name is null.

EDIT (judge harshly): My display() method won't display and I'm not sure why

I recently posted a question in regards to my display() method only displaying certain objects, and was able to correct that with some feedback I received earlier in regards to my toString() method. However, I had to change my idNum to an int, and now my displayMethod() won't display at all. I tried retracing my steps and am unsure what happened.
The object array that is supposed to hold an identification number, a sales amount, and the persons name. However, when I display the array, nothing is displaying. I've tried the for loop, enhanced for loop and tried just a system.out.print invoking the get() methods.
I don't know if it has something to do with my displayDatabase() method, the way I am using my Scanner variable (USER_INPUT) to set the data entered, or something to do with my constructors.
My constructor looks like this:
==================================================
public class Salesperson
{
private String salesName;
private int salesID;
private double annualSales;
public Salesperson(String salesName, int salesIDNum, double yearlySales)
{
this.salesName = salesName;
salesID = salesIDNum;
annualSales = yearlySales;
}
public String getSalesName()
{
return salesName;
}
public void setSalesName(String salesName)
{
this.salesName = salesName;
}
public double getSalesID()
{
return salesID;
}
public void setSalesID(int salesIDNum)
{
salesID = salesIDNum;
}
public double getAnnualSales()
{
return annualSales;
}
public void setAnnualSales(double yearlySales)
{
annualSales = yearlySales;
}
#Override
public String toString()
{
return String.format("%s-%-10s%-10.2f", salesName,
salesID, annualSales);
}
}
And my code for application looks like this:
import java.util.Arrays;
import java.util.Scanner;
public class CreateSalesperson
{
private static final Scanner USER_INPUT = new Scanner(System.in);
private static final int UPPER_SIZE_LIMIT = 20;
private static final int LOWER_SIZE_LIMIT = 0;
private static Salesperson[] salesStaffInDatabase = new
Salesperson[20];
private static int numOfSalesPpl = 0;
private static boolean loop = true;
public static void main(String[] args)
{
String selection;
selection = programMenu();
String response;
while(loop)
switch(selection)
{
case "A":
if(numOfSalesPpl == UPPER_SIZE_LIMIT)
{
System.out.print("Database has reached capacity.");
System.out.print(" Please delete a record before ");
System.out.println("adding to the database.");
}
else
{
addRecord();
}
break;
case "a":
if(numOfSalesPpl == UPPER_SIZE_LIMIT)
{
System.out.print("Database has reached capacity.");
System.out.print(" Please delete a record before ");
System.out.println("adding to the database.");
}
else
{
addRecord();
}
break;
case "C":
if(numOfSalesPpl == LOWER_SIZE_LIMIT)
{
System.out.print("Database is empty. ");
System.out.print("Please add a record.");
}
else
{
changeRecord();
}
break;
case "c":
if(numOfSalesPpl == LOWER_SIZE_LIMIT)
{
System.out.print("Database is empty. ");
System.out.print("Please add a record.");
}
else
{
changeRecord();
}
break;
case "E":
System.out.print("You Are Leaving Database");
loop = false;
break;
case "e":
System.out.print("You Are Leaving Database");
loop = false;
break;
}
}
public static void changeRecord()
{
String idNum;
String salesName;
double salesAmount;
String response;
System.out.print("Enter Sales ID: ");
idNum = USER_INPUT.nextLine();
if(isValidID(idNum))
{
int searchResult = Arrays.binarySearch(salesStaffInDatabase, idNum);
System.out.println(salesStaffInDatabase[searchResult]);
}
else
{
System.out.println("Invalid Sales ID");
}
}
public static boolean isValidID(String idNum)
{
boolean isValid= false;
for(int val = 0;val < numOfSalesPpl && !isValid; ++val)
{
if(salesStaffInDatabase[val].equals(idNum))
{
isValid = true;
}
}
return isValid;
}
public static void addRecord()
{
int idNum;
String salesName;
double salesAmount;
String idNo;
String response;
do
{
System.out.print("Please enter sales ID: ");
idNum = USER_INPUT.nextInt();
idNo = Integer.toString(idNum);
if(idNo.length() != 8)
System.out.println("Sales ID must be 8 digits long: ");
}
while(idNo.length() < 8 || idNo.length() > 8);
System.out.print("Name: ");
salesName = USER_INPUT.nextLine();
USER_INPUT.nextLine();
System.out.print("Sales Amount: ");
salesAmount = Double.parseDouble(USER_INPUT.nextLine());
salesStaffInDatabase[numOfSalesPpl] = new
Salesperson(salesName,idNum,salesAmount);
salesStaffInDatabase[numOfSalesPpl].setSalesName(salesName);
salesStaffInDatabase[numOfSalesPpl].setSalesID(idNum);
salesStaffInDatabase[numOfSalesPpl].setAnnualSales(salesAmount);
System.out.print("Do you want to display database Y/N?: ");
response = USER_INPUT.nextLine();
while(response.equalsIgnoreCase("Y")||response.equalsIgnoreCase("yes"))
{
displayDatabase();
}
}
public static void displayDatabase()
{
for(int val=0;val < numOfSalesPpl; val++)
{
System.out.println(salesStaffInDatabase[val]);
}
}
public static String programMenu()
{
String selection;
do
{
System.out.println("(A)dd a Record");
System.out.println("(C)hange a Record");
System.out.println("(E)xit Database");
System.out.print("Enter selection: ");
selection = USER_INPUT.nextLine();
}
while(!selection.equalsIgnoreCase("a") &&
!selection.equalsIgnoreCase("c")
&& !selection.equalsIgnoreCase("e"));
return selection;
}
}
=================================================================

In Java, whenever you want to display an object as string, you must override the toString() method.
The code that you posted, the Salesperson's toString() method returns only the salesID and anualSales. If you want to display another attribute, you must place it in the toString() method.
If you want to display the first name on the beginning of the output, you can do:
#Override public String toString() {
return String.format("%s - %-10s%-10.2f", salesFirstName, salesID, annualSales);
}

edit the toString()method in Salesperson class :
#Override
public String toString() {
return "Salesperson{" +
"salesFirstName='" + salesFirstName + '\'' +
", salesLastName='" + salesLastName + '\'' +
", salesID='" + salesID + '\'' +
", annualSales=" + String.format("%-10.2f", annualSales)+
'}';
}

Set up while statement to print out methods?

Not the best title but basically I want to ask the user to enter a temperature, and then displays a list of substances that will freeze at that temperature and those that boil at that temperature. I want it to be in a while loop and I want the user to be able to go until they want to stop. Heres what I have so far, my first class and then a tester
public class FreezingPoint {
private int temperature;
public double getTemperature() {
return temperature;
}
public void setTemperature() {
this.temperature = temperature;
}
public boolean isEthylFreezing() {
boolean status;
if (temperature <= -173.0)
status = true;
else
status = false;
return status;
}
public boolean isEthylBoiling() {
boolean status;
if (temperature >= 172.0)
status = true;
else
status = false;
return status;
}
public boolean isOxygenFreezing() {
boolean status;
if (temperature <= -362.0)
status = true;
else
status = false;
return status;
}
public boolean isOxygenBoiling() {
boolean status;
if (temperature >= -306.0)
status = true;
else
status = false;
return status;
}
public boolean isWaterFreezing() {
boolean status;
if (temperature <= 32)
status = true;
else
status = false;
return status;
}
public boolean isWaterBoiling() {
boolean status;
if (temperature >= 212)
status = true;
else
status = false;
return status;
}
}
and now tester class
import java.util.Scanner;
public class TestFreezingPoint {
public static void main(String[] args) {
FreezingPoint fp = new FreezingPoint();
double temperature;
Scanner sc = new Scanner(System.in);
System.out.println("please enter a temp");
temperature = sc.nextDouble();
System.out.println("Is Water Freezing?" + fp.isWaterFreezing());
}
}
My problem is that the code isn't working properly and I'm confused as to where to go from here. I know how to setup the while loop and how to make it go until I want to stop but I'm not sure on how to properly print out the list of substances that will be displayed based off the users inputted temperature
Any help appreciated, pretty new to java and been stuck on this awhile
Thanks

I think you should use a different way of testing if something boils or freezes at a given temperature. In your example you would have to add two methods for every substance and then find a way to cycle through them.
It would probably be a lot easier if you used for example a list and then use a switch() statement to only add the substances to the list that boil or freeze at the given temperature. If you make a method that does so and give it the temperature as a parameter and have it return the populated list, you could easily loop through the list and print out every element.
I made a quick example for you:
public List<String> getSubstances(int temperature){
List<String> substances = new ArrayList<String>();
switch(temperature){
case 0:
substances.add("Water");
case 100:
substances.add("Water");
}
return substances;
}
This would be a way easier solution and you can cycle through the list very easily to print it out.

I would suggest to use a class to represent the substances:
public class Substance {
private String name;
private double tempFreeze;
private double tempBoil;
public Substance(String name, double tempFreeze, double tempBoil) {
this.name = name;
this.tempFreeze = tempFreeze;
this.tempBoil = tempBoil;
}
public double getTempBoil() { return tempBoil; }
public double getTempFreeze() { return tempFreeze; }
public String getName() { return name; }
public String getState(double temp) {
if (temp <= tempFreeze) {
return "freeze";
} else if (temp >= tempBoil) {
return "boil";
}
return "liquid";
}
}
To be used like :
public static void main(String[] args) {
List<Substance> list = new ArrayList<>();
list.add(new Substance("ethyl", -173, 172));
list.add(new Substance("Oxygen", -362, -306));
list.add(new Substance("water", 32, 212));
Scanner sc = new Scanner(System.in);
do {
System.out.println("please enter a temp");
double temperature = sc.nextDouble();
sc.nextLine(); //consume return char
for (Substance s : list) {
System.out.println(s.getName() + " is in state : " + s.getState(temperature));
}
System.out.println("\nDo you want to stop ? Write 'yes' to stop");
} while (!sc.nextLine().contains("y"));
}
Execution example :
please enter a temp
125
ethyl is in state : liquid
Oxygen is in state : boil
water is in state : liquid
Do you want to stop ? Write 'yes' to stop
y

Trying to use 2 objects in Java

My goal is to have 2 different objects fight each other, and show the results. My problem is I cant figure out how to set the attack and health properly so that it actually updates the way it is supposted to.
import java.util.Random;
import java.util.Scanner;
/**
*
* #author Brenton
*/
public class Fighter {
private String name;
private int attack;
private int level = 1;
private int health = 50;
private boolean isAlive = true;
private Fighter fighterTwo;
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
public int getAttack() {
Random generator = new Random();
attack = generator.nextInt(10) * level + 1;
return attack;
}
public void setAttack(int attack) {
this.attack = attack;
}
public int getLevel() {
if(level >= 60)
{
level = 60;
}
return this.level;
}
public void setLevel(int level) {
this.level = level;
}
public int getHealth() {
if(this.health <= 0)
{
this.health = 0;
}
return this.health;
}
public void setHealth(int health) {
this.health = health;
}
public boolean isAlive() {
if(this.health <= 0)
{
this.isAlive = false;
}
return this.isAlive;
}
public static String getWelcome() {
String welcome = "Hello and welcome to FightClub, do you wish to fight, yes or no? ";
return welcome;
}
public String getPunch(Fighter fighterTwo) {
this.fighterTwo = fighterTwo;
String hit = "You choose to punch the other fighter and dealt " + getAttack() + " damage, your opponent now has " + this.decreaseHitPoints(fighterTwo) + " health remaining";
return hit;
}
public int decreaseHitPoints(Fighter fighterTwo) {
this.fighterTwo = fighterTwo;
int health = fighterTwo.getHealth();
int attack = getAttack();
health = health - attack;
return health;
}
public static String invalidInput() {
String invalid = "I am sorry that is not a valid input option ";
return invalid;
}
public void getWinner(Fighter fighterTwo) {
this.fighterTwo = fighterTwo;
if(this.isAlive() == false && fighterTwo.isAlive() == false)
{
System.out.println("Both fighters have fallen heroically");
}
else if(this.isAlive() == true && fighterTwo.isAlive() == false)
{
System.out.println(this.getName() + " is victorious! ");
}
else if(this.isAlive() == false && fighterTwo.isAlive() == true)
{
System.out.println(fighterTwo + " is victorious! ");
}
else
{
System.out.println("ERROR ERROR ERROR");
}
}
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
Fighter a = new Warrior();
Fighter b = new Dragon();
System.out.print(getWelcome());
while(in.hasNextLine())
{
switch(in.nextLine())
{
case "no":
System.out.println("Wow, you are not even gonna try, you have lost!");
break;
case "yes":
System.out.println("Let the fight begin! ");
while(a.isAlive() && b.isAlive())
{
System.out.println("Do you want to punch, kick, or headbutt the other fighter? ");
switch(in.nextLine())
{
case "punch":
System.out.println(a.getPunch(b));
break;
/*case "kick":
System.out.println(a.getKick(b));
break;
case "headbutt":
System.out.println(a.getHeadbutt(b));
break;*/
default :
System.out.println(invalidInput());
break;
}
}
default:
System.out.println(invalidInput());
break;
}//end of first switch statement
}//end of first while loop
}//end of main
}

You're calculating the attack correctly. You're just not updating the state of the other fighter.
In your main() method you launch the attack with
System.out.println(a.getPunch(b));
That's just fine. a throws a Punch at b, then you print out the hit points returned from getPunch(). So let's dig deeper into getPunch() to try to find the problem.
In getPunch() you end up invoking
this.decreaseHitPoints(fighterTwo)
while constructing the return String. This seems like the right approach, so is there a problem in decreaseHitPoints()?
public int decreaseHitPoints(Fighter fighterTwo) {
this.fighterTwo = fighterTwo;
int health = fighterTwo.getHealth();
int attack = getAttack();
health = health - attack;
return health;
}
You assign the fighterTwo argument to your fighterTwo field. Not sure why, but that's not wrong per se. Then you get his health into a local variable called health. Then you get the attack into a local variable called attack. Then you subtract attack from health, and then return the calculated value. But you never update the health value on fighterTwo! So you just need one more line in your program: right before your return statement, insert
fighterTwo.setHealth(health);

Accepting method parameters in Java

my problem is confusing me because I have done this before and it worked in previous programs but this particular program will not work. I just need to use the method typeInput and popularityNumber with the 2 variables I passed to them but I cannot call them in my main method without error. Either a ")" or ";" expected occurs, and it looks to me like there are parenthesis and semi colons where needed. I'm sure it's a quick fix and would appreciate learning how to fix it. Thank you!
public static void main(String[] args) {
// TODO code application logic here
nameInput();
typeInput(Scanner keyboard, CartoonStar star);
popularityNumber();
}
/**
*
* #param name
*/
public static void nameInput() {
System.out.println("What is the name of the cartoon character : ");
Scanner keyboard = new Scanner(System.in);
CartoonStar star = new CartoonStar();
String name = keyboard.next();
star.setName(name);
}
public static void typeInput(Scanner keyboard, CartoonStar star){
System.out.println("What is the cartoon character type: 1 = FOX,2 = CHICKEN,3 = RABBIT,4 = MOUSE,5 = DOG,\n"
+ "6 = CAT,7 = BIRD,8 = FISH,9 = DUCK,10 = RAT");
switch (keyboard.nextInt())
{case 1 :
star.setType(CartoonType.FOX);
break;
case 2 :
star.setType(CartoonType.CHICKEN);
break;
case 3 :
star.setType(CartoonType.RABBIT);
break;
case 4 :
star.setType(CartoonType.MOUSE);
break;
case 5 :
star.setType(CartoonType.DOG);
break;
case 6 :
star.setType(CartoonType.CAT);
break;
case 7 :
star.setType(CartoonType.BIRD);
break;
case 8 :
star.setType(CartoonType.FISH);
break;
case 9 :
star.setType (CartoonType.DUCK);
break;
case 10 :
star.setType(CartoonType.RAT);
break;
}
}
public static void popularityNumber(Scanner keyboard, CartoonStar star){
System.out.println("What is the cartoon popularity number?");
int popularity = keyboard.nextInt();
star.setPopularityIndex(popularity);
System.out.println(star.getName() + star.getType() + star.getPopularityIndex());
}
}
CartoonStar class (just in case you want it):
public class CartoonStar {
private String name;
private CartoonStar.CartoonType type;
enum CartoonType {
FOX(1),CHICKEN(2),RABBIT(3),MOUSE(4),DOG(5),CAT(6),BIRD(7),FISH(8),DUCK(9),RAT(10);
private final int animalType;
private static Map <Integer, CartoonType> map = new HashMap <Integer, CartoonType>();
private CartoonType(int animalType){
this.animalType=animalType;
}
public int getAnimlType(){
return animalType;}
}//enum types
private int popularityIndex; //1 to 10 10 being the most popular
public CartoonStar() {
}//end no argument construtor
public CartoonStar(String name,CartoonStar.CartoonType type, int popularityIndex) {
setName(name);
setType(type);
setPopularityIndex(popularityIndex);
}//end full constructor
//getters and setters
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setType(CartoonStar.CartoonType type) {
this.type = type;
}
public CartoonStar.CartoonType getType() {
return type;
}
public void setPopularityIndex(int popularityIndex){
this.popularityIndex = popularityIndex;
}
public int getPopularityIndex(){
return popularityIndex;
}
}

In your main method, you call your method as follows:
typeInput(Scanner keyboard, CartoonStar star);
The typeInput method expects a declared keyboard and declared star. You have called it incorrectly.
Your best option will be as follows:
public static void main(String[] args) {
// TODO code application logic here
nameInput();
popularityNumber();
}
public static void nameInput() {
System.out.println("What is the name of the cartoon character : ");
Scanner keyboard = new Scanner(System.in);
CartoonStar star = new CartoonStar();
String name = keyboard.next();
star.setName(name);
typeInput(keyboard, star);
}
I added typeInput() in your nameInput() method and removed it from the main() method.