我正在编写一个应该玩HiLo游戏的程序。 HiLo是一款游戏，其中会生成一个随机数，玩家必须猜测它。如果他们猜错了，他们会被告知答案是高于还是低于他们的猜测，然后允许他们再次猜测。如果需要，我的程序应该能够限制猜测的数量，设置可以从中选择答案的值的范围（因此也可以猜测的范围）。我还需要选择一个人是否会玩游戏，或者是否让计算机玩，如果是的话，以什么技能水平（差，中，好）进行选择。
我已经写了3类：GameManager，HiLo和Player。
GameManager类允许玩多个游戏并跟踪获胜次数。
public class GameManager {
private HiLo game;
private int wins;
private int totalRounds;
private int player;
/**
* Constructor for objects of class GameManager
*/
public GameManager()
{
player = 2;
}
public void playGames(int rounds)
{
int i = 0;
while(i < rounds) {
game = new HiLo(player);
game.play();
wins += game.getHasWon();
i++;
}
totalRounds += rounds;
}
public void changePlayer(int playerType)
{
player = playerType;
}
} //This should be indented better, but it won't format properly, apologies
HiLo课程基本上是设置并玩HiLo的个人游戏。
public class HiLo {
private int guessLimit;
private int lowerLimit;
private int upperLimit;
private int guesses;
private int answer;
private boolean hasWon;
private Player player;
private String result;
/**
* Constructor for objects of class HiLo
*/
public HiLo(int playerType) //Set default values
{
guessLimit = 10;
lowerLimit = 0;
upperLimit = 50;
hasWon = false;
player = new Player(playerType);
}
public HiLo(int guessLimit, int lowerLimit, int upperLimit, int playerType) //Overload
{
this.guessLimit = guessLimit;
this.lowerLimit = lowerLimit;
this.upperLimit = upperLimit;
hasWon = false;
player = new Player(playerType);
}
//Returns lower limit
public int getLowerLimit()
{
return lowerLimit;
}
//Returns upper limit
public int getUpperLimit()
{
return upperLimit;
}
//Returns 1 if hasWon is true and 0 if hasWon is false
public int getHasWon()
{
if(hasWon) {
return 1;
} else {
return 0;
}
}
//Returns the number of guesses so far
public int getGuesses()
{
return guesses;
}
//Play a game of HiLo
public void play()
{
answer = randInt(lowerLimit, upperLimit);
guesses = 0;
while(guesses < guessLimit) {
int guess = player.guess(); //This gets a guess from the player
result = isCorrect(guess); //Was the guess correct?
if(result.equals("Win")) {
break; //If the player has won, break from the while loop
}
guesses++;
}
}
//Checks if the guess was correct
public String isCorrect(int guess)
{
if(guess == answer) {
hasWon = true;
return "Win";
} else if(guess < answer) {
lowerLimit = guess;
return "Higher";
} else {
upperLimit = guess;
return "Lower";
}
}
public int randInt(int min, int max)
{
Random rand = new Random();
int randomNum = rand.nextInt((max - min) + 1) + min;
return randomNum;
}
}
玩家类别确定哪个玩家正在玩（0 =人类，1 = badComp，2 = medComp，3 = goodComp）以及他们将用来猜测的策略。
import java.util.Random;
import java.util.Scanner;
public class Player {
private int playerType;
private HiLo game;
private int range;
private int lowestLimit; //This is the starting value of lowerLimit
/**
* Constructor for objects of class Player
*/
public Player(int playerType)
{
if(playerType < 0 || playerType > 3) {
System.out.println("ERROR. Please pick a valid playerType");
}
this.playerType = playerType;
range = 0;
range = setRange();
lowestLimit = game.getLowerLimit();
}
public int guess()
{
if(playerType == 0) {
return humanPlayer();
} else if(playerType == 1) {
return badComputerPlayer();
} else if(playerType == 2) {
return mediumComputerPlayer();
} else {
return goodComputerPlayer();
}
}
//Guess from a good computer player
public int goodComputerPlayer()
{
return (game.getUpperLimit() - game.getLowerLimit())/2;
}
//Guess from a medium computer player
public int mediumComputerPlayer()
{
return randInt(game.getLowerLimit(), game.getUpperLimit());
}
//Guess from a bad computer player
public int badComputerPlayer()
{
return randInt(lowestLimit, range);
}
public int humanPlayer()
{
Scanner keyboard = new Scanner(System.in);
System.out.println("enter an integer");
int myint = keyboard.nextInt();
return myint;
}
//Generates a random number in the range maz-min
public int randInt(int min, int max)
{
Random rand = new Random();
int randomNum = rand.nextInt((max - min) + 1) + min;
return randomNum;
}
//Set the range of values to guess from for bad player
public int setRange()
{
int r = game.getUpperLimit() - game.getLowerLimit();
return r;
}
}
当我从HiLo类创建对象并输入所有参数时，出现NullPointException：
java.lang.NullPointerException
at Player.setRange(Player.java:75)
at Player.<init>(Player.java:26)
at HiLo.<init>(HiLo.java:35)
我是编程和Java的新手，这是我的第一个NullPointException错误。我已经阅读了其他一些文章，但我无法弄清楚。
我也不认为播放器类也不完全按照我的要求做。从概念上讲，Player类的每个新实例都与创建该实例的HiLo游戏实例相关，因为HiLo游戏一次只能有一个玩家。我希望Player类的新实例引用创建它的HiLo类的实例：
lowestLimit = game.getLowerLimit();
我正在尝试将lowerLimit =设置为创建此Player实例的HiLo游戏实例的下限，但是我认为这只是引用从HiLo类创建的对象游戏，而不是创建此实例的实例。播放器实例。抱歉，如果这令人困惑，我正在尽力解释:)
我也在Player类中的许多其他方法中执行此操作。我已经读过一些有关使用反射来潜在地解决此问题的知识，但我真的不确定我是否理解。
任何帮助和/或想法将不胜感激，
谢谢。
编辑：只是以为我会让你知道我正在使用BlueJ环境。
最佳答案
setRange()方法取决于game不是null。因为setRange()是在Player的构造函数中调用的，所以由于NullPointerException实例变量尚未初始化，因此它将始终抛出game。
解决此问题的一种方法是使Player的构造函数接受HiLo参数，并在调用game之前将setRange()设置为该值：
public Player(int playerType, HiLo game) {
this.game = game;
// ...
}
现在，您需要更新
player = new Player(playerType);语句以使用正确的参数。因为该语句在HiLo的实例方法中，所以我们可以简单地将this作为第二个参数传递：player = new Player(playerType, this);