我目前正在编写一个小游戏的编码过程，其中有进度条从不同的类中获取变量的值。 进度条从0到500，可以调用不同的方法来改变进度条测量的变量值。
happyBar = new JProgressBar();
happyBar.setMinimum(0);
happyBar.setMaximum(500);
happyBar.setValue(cat.getHappy());
happyBar.repaint();
happyLabel = new JLabel("Happy");
happyLabel.setForeground(Color.white);
我引用的cat.getHappy（）似乎引发了一个错误。 当我添加这行代码时，该方法是可见的：
public static Cat cat;
有没有人有任何想法，为什么我不能通过将cat.getHappy作为当前值来更新JProgressBar？
完整代码：
接口类：
import java.awt.color.*;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridLayout;
import java.awt.Dimension;
import java.util.Timer;
import java.util.TimerTask;
import java.awt.image.BufferedImage;
import java.io.File;
import javax.imageio.ImageIO;
import javax.swing.*;
public class Cat_Interface {
private JFrame catWindow;
private JPanel topPanel, leftPanel, rightPanel, bottomPanel, allPanels, playPanel, sleepPanel, huntPanel, feedPanel, cleanPanel, walkPanel, drinkPanel;
private JLabel catLabel, happyLabel, hungryLabel, energyLabel, hygieneLabel, weightLabel, thirstLabel, picLabel;
private JButton play, sleep, feed, hunt, clean, walk, drink;
private JProgressBar happyBar, hungryBar, energyBar, thirstBar, weightBar, hygieneBar;
private JTextArea catText;
private JProgressBar happy, hungry, energy, thirst, weight, hygiene;
private int interval;
private Timer timer;
public Cat_Interface(Cat cat) {
topPanel = new JPanel();
topPanel.setBackground(Color.lightGray);
leftPanel = new JPanel();
leftPanel.setBackground(Color.lightGray);
rightPanel = new JPanel();
rightPanel.setBackground(Color.gray);
bottomPanel = new JPanel();
bottomPanel.setBackground(Color.darkGray);
allPanels = new JPanel();
allPanels.setLayout(new BoxLayout(allPanels, BoxLayout.Y_AXIS));
topPanel.setLayout(new GridLayout(2,0));
play = new JButton("Play");
sleep = new JButton("Sleep");
feed = new JButton("Feed");
hunt = new JButton("Hunt");
clean = new JButton("Clean");
walk = new JButton("Walk");
drink = new JButton("Drink");
bottomPanel.setBorder(BorderFactory.createEmptyBorder(25,25,25, 25));
bottomPanel.setLayout(new GridLayout(0, 4, 50, 10));
bottomPanel.add(play);
bottomPanel.add(sleep);
bottomPanel.add(feed);
bottomPanel.add(hunt);
bottomPanel.add(clean);
bottomPanel.add(walk);
bottomPanel.add(drink);
leftPanel.setBorder(BorderFactory.createEmptyBorder());
ImageIcon image = new ImageIcon("images/cat_test_picture.svg");
leftPanel.add(new JLabel(image));
leftPanel.setVisible(true);
rightPanel.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
rightPanel.setLayout(new GridLayout(0, 1));
happyBar = new JProgressBar();
happyBar.setMinimum(0);
happyBar.setMaximum(500);
//happyBar.setValue(cat.getHappy());
happyBar.repaint();
happyLabel = new JLabel("Happy");
happyLabel.setForeground(Color.white);
hungryBar = new JProgressBar(0,500);
hungryLabel = new JLabel("Hungry");
hungryBar.repaint();
hungryLabel.setForeground(Color.white);
energyBar = new JProgressBar(0,500);
energyLabel = new JLabel("Energy");
energyBar.repaint();
energyLabel.setForeground(Color.white);
hygieneBar = new JProgressBar(0,500);
hygieneBar.setIndeterminate(true);
hygieneLabel = new JLabel("Hygiene");
hygieneBar.repaint();
hygieneLabel.setForeground(Color.white);
thirstBar = new JProgressBar(0,500);
thirstLabel = new JLabel("Thirst");
thirstBar.repaint();
thirstLabel.setForeground(Color.white);
weightBar = new JProgressBar(0,500);
weightLabel = new JLabel("Weight");
weightBar.repaint();
weightLabel.setForeground(Color.white);
rightPanel.add(happyBar);
rightPanel.add(happyLabel);
happyLabel.setBounds(5, 5, 5, 5);
happyBar.setBounds(15, 5, 5, 5);
rightPanel.add(hungryBar);
rightPanel.add(hungryLabel);
hungryLabel.setBounds(5, 5, 5, 5);
hungryBar.setBounds(15, 5, 5, 5);
rightPanel.add(energyBar);
rightPanel.add(energyLabel);
energyLabel.setBounds(5, 5, 5, 5);
energyBar.setBounds(15, 5, 5,5);
rightPanel.add(hygieneBar);
rightPanel.add(hygieneLabel);
hygieneLabel.setBounds(5, 5, 5, 5);
hygieneBar.setBounds(15, 5, 5, 5);
rightPanel.add(thirstBar);
rightPanel.add(thirstLabel);
thirstLabel.setBounds(5, 5, 5, 5);
thirstBar.setBounds(15, 5, 5, 5);
rightPanel.add(weightBar);
rightPanel.add(weightLabel);
weightLabel.setBounds(5, 5, 5, 5);
weightBar.setBounds(15, 5, 5, 5);
allPanels.add(topPanel);
allPanels.add(leftPanel);
allPanels.add(bottomPanel);
allPanels.add(rightPanel);
catWindow = new JFrame();
catWindow.setTitle("Tamagotchi Game: Cat");
catWindow.setSize(550,300);
catWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
catWindow.setVisible(true);
catWindow.add(allPanels);
catWindow.getContentPane().add(leftPanel,BorderLayout.WEST);
catWindow.getContentPane().add(rightPanel,BorderLayout.EAST);
catWindow.getContentPane().add(bottomPanel,BorderLayout.SOUTH);
//catWindow.getContentPane().add(topPanel,BorderLayout.NORTH);
}
public JButton getPlayButton() {
return play;
}
public JButton getSleepButton() {
return sleep;
}
public JButton getFeedButton() {
return feed;
}
public JButton getHuntButton() {
return hunt;
}
public JButton getWalkButton() {
return walk;
}
public JButton getDrinkButton() {
return drink;
}
public JButton getCleanButton() {
return clean;
}
public JPanel getPanels() {
return allPanels;
}
}
猫类：
import java.util.Calendar;
import java.util.GregorianCalendar;
import javax.swing.JOptionPane;
// my own pet class for the cat animal I chose.
public class Cat extends Animal {
Cat_Interface cat = new Cat_Interface(this);
private long tDelta, tEnd;
private long tStart = System.currentTimeMillis();
private String furColour, eyeColour;
public int whiskerLength, petDay, petMonth, petYear, ageInYears, ageInMonths, ageInDays;
public Cat(String aName, Gender aGender ,String aTrait,String aAgeEffect, DateOfBirth aDateOfBirth,int aWeight, int aPetDay, int aPetMonth, int aPetYear, int aWhiskerLength, String aFurColour, String aEyeColour){
super(aName, aGender , aTrait, aWeight, aDateOfBirth, aAgeEffect);
petDay = aPetDay;
petMonth = aPetMonth;
petYear = aPetYear;
whiskerLength = aWhiskerLength;
furColour = aFurColour;
eyeColour = aEyeColour;
if (super.getHungry() <=0) {
Death();
JOptionPane.showMessageDialog(null, "Reason:\nYou didn't feed it enough.");
}
if (super.getEnergy() <=0) {
super.passOut();
}
if (super.getWeight() >=100) {
Death();
JOptionPane.showMessageDialog(null, "Reason:\nIt was too heavy.");
}
}
// getters
public String getFurColour() {
return furColour;
}
public int getWhiskerLength() {
return whiskerLength;
}
public String getEyeColour() {
return eyeColour;
}
// setters
public void setFurColour(String aFurColour) {
furColour = aFurColour;
}
public void setWhiskerLength(int aWhiskerLength) {
whiskerLength = aWhiskerLength;
}
public void setEyeColour(String aEyeColour) {
eyeColour = aEyeColour;
}
//custom methods
public void hunt() {
//my custom method for the cat. This enables the cat to hunt for food when it is too hungry.
super.setHappy(super.getHappy() - 10);
super.setEnergy(super.getEnergy() - 20);
super.setHungry(super.getHungry() + 30);
JOptionPane.showMessageDialog(null, super.getName() + " has hunted and consumed some food. \nFeed " +super.getName() + " more in the future so he doesn't have to do this.");
}
public void cleanSelf() {
// my custom method for the cat. Cats clean themselves and become happier and , obviously, cleaner as a result.
JOptionPane.showMessageDialog(null, super.getName() + " has cleaned itself as you have not cleaned it in a while.");
super.setHygiene(super.getHygiene() + 20);
super.setHappy(super.getHappy() + 10);
}
//overridden methods from the animal class
@Override
//method to feed the cat, overriding the feed method from the animal class.
public void feed() {
if (super.getHungry() > 50) {
super.setHungry(super.getHungry() + 60);
super.setWeight(super.getWeight() + 5);
super.setEnergy(super.getEnergy() + 20);
JOptionPane.showMessageDialog(null, "You have fed " + super.getName());
} else {
JOptionPane.showMessageDialog(null, "You cannot feed " + super.getName() + " as they are not hungry. \nWait for the hungriness to fall below 50.");
}
}
@Override
public void clean() {
super.setHygiene(super.getHygiene() + 30);
super.setHappy(super.getHappy() - 20);
JOptionPane.showMessageDialog(null, "You have cleaned " + super.getName());
}
@Override
public void play() {
if (super.getEnergy() >= 50 ) {
super.setHappy(super.getHappy() + 60);
super.setEnergy(super.getEnergy() - 40);
super.setHungry(super.getHungry() - 50);
JOptionPane.showMessageDialog(null, "You have played with " + super.getName() + " and they are happy.");
} else {
JOptionPane.showMessageDialog(null, "You must let " + super.getName() + " rest before you can play with them." + "\nThe energy level must be above 50 to play.");
}
}
@Override
public void sleep() {
if (super.getEnergy() <= 120) {
super.setHappy(super.getHappy() + 30);
super.setHungry(super.getHungry() - 50);
super.setEnergy(super.getEnergy() + 50);
JOptionPane.showMessageDialog(null, "You have put " + super.getName() + " to sleep.");
} else {
JOptionPane.showMessageDialog(null, "You cannot put " + super.getName() + " to sleep until their energy is below 120." + "\nPlay with them more to decrease the energy level.");
}
}
@Override
public void passOut() {
super.setHappy(super.getHappy() - 30);
JOptionPane.showMessageDialog(null, super.getName() + " has passed out due to being too tired.");
}
// A method that when called will produce a pop up window with the cat's stats.
public void showStats() {
JOptionPane.showMessageDialog(null, "Name: " + super.getName()+ "\nAge: " + findAgeInYears() + " years, " + findAgeInMonths() + " months and " + findAgeInDays() + " days old." +
"\nTrait: " + super.getTrait() + "\nHungry: " + super.getHungry() + "\nEnergy: " + super.getEnergy() +
"\nHappy: " + super.getHappy() + "\nHygiene: " + super.getHygiene() + "\nWeight: " + super.getWeight() + "\nThirst: " + super.getThirst() + "\nTime spent together: " + getTimeSpent() +" seconds");
}
// A method that allows you to take the cat on a walk.
public void walk() {
if (super.getEnergy() >= 50) {
super.setHappy(super.getHappy() + 60);
super.setEnergy(super.getEnergy() - 40);
super.setHungry(super.getHungry() - 10);
super.setHygiene(super.getHygiene() - 30);
JOptionPane.showMessageDialog(null, "You have taken " + super.getName() + " for a walk.");
} else {
JOptionPane.showMessageDialog(null, "The energy must be above 40 for " + super.getName() + " to be able to go for a walk.");
}
}
// This method will kill the cat when certain stats are reached eg hungry <= 0
@Override
public void Death() {
JOptionPane.showMessageDialog(null, super.getName() + " has died.\nLook after your pets in the future.");
System.exit(5);
}
//This method will calculate the time spent with the cat.
public double getTimeSpent() {
tEnd = System.currentTimeMillis();
tDelta = tEnd - tStart;
double elapsedSeconds = tDelta / 1000.0;
return elapsedSeconds;
}
@Override
public void drink() {
super.setThirst(super.getThirst() + 50);
}
@Override
public void runAway() {
JOptionPane.showMessageDialog(null, super.getName() + " has run away. Take better care of them in the future.");
System.exit(5);
}
/**
* This handy method findAgeInYears() uses a gregorian calendar to give me the value for the age of the animal in years. It uses the aPetMonth variable that is passed
* in through the constructor and uses it in it's calculations.
* @return the age in years.
*/
public int findAgeInYears(){
Calendar cal1 = new GregorianCalendar();
int tempMonth = (petMonth - 1);
cal1.add(Calendar.DAY_OF_MONTH, -petDay);
cal1.add(Calendar.MONTH, -(tempMonth));
cal1.add(Calendar.YEAR, -petYear);
ageInYears= (cal1.get(Calendar.YEAR));
return ageInYears;
}
/**
* This handy method findAgeInMonths() uses a gregorian calendar to give me the value for the age of the animal in months. It uses the aPetMonth variable that is passed
* in through the constructor and uses it in it's calculations.
* @return the age in months.
*/
public int findAgeInMonths(){
Calendar cal1 = new GregorianCalendar();
int tempMonth = (petMonth - 1);
cal1.add(Calendar.DAY_OF_MONTH, -petDay);
cal1.add(Calendar.MONTH, -(tempMonth));
cal1.add(Calendar.YEAR, -petYear);
ageInMonths = (cal1.get(Calendar.MONTH));
return ageInMonths;
}
/**
* This handy method findAgeInDays() uses a gregorian calendar to give me the value for the age of the animal in days. It uses the aPetDay variable that is passed
* in through the constructor and uses it in it's calculations.
* @return the age in days.
*/
public int findAgeInDays(){
Calendar cal1 = new GregorianCalendar();
int tempMonth = (petMonth - 1);
cal1.add(Calendar.DAY_OF_MONTH, -petDay);
cal1.add(Calendar.MONTH, -(tempMonth));
cal1.add(Calendar.YEAR, -petYear);
ageInDays = (cal1.get(Calendar.DAY_OF_MONTH));
return ageInDays;
}
}
动物类：
import java.util.Calendar;
import java.util.GregorianCalendar;
/**
* This is the generic super class animal witch will be inherited by
* each individual animal. It contains generic instance variables and methods.
*
* @author Group 5 Tuesday
*
*/
public class Animal {
private String name, trait, ageEffect;
private Gender gender;
private DateOfBirth dateOfBirth;
private int happy, hungry, energy, weight, hygiene, age, thirst;
/**
* This is the constructor for the animal class. It initialises all the instance
* variables for the animal class.
* @param aName - The name of the animal
* @param aTrait - The trait of the animal
* @param aWeight - the weight of the animal
* @param aDateOfBirth - the date of birth of the animal
*/
public Animal (String aName,Gender aGender ,String aTrait, int aWeight, DateOfBirth aDateOfBirth, String aAgeEffect)
{
name = aName;
gender = aGender;
dateOfBirth = aDateOfBirth;
age = 2014 - dateOfBirth.getYear();
trait = aTrait;
happy = 500;
energy = 500;
hungry = 500;
weight = aWeight;
hygiene = 500;
thirst = 500;
ageEffect = aAgeEffect;
}
// getter and setter methods
/**
* This method returns the animal name
* @return the name
*/
public String getName() {
return name;
}
/**
*
* @return the gender of the animal
*/
public Gender getGender()
{
return gender;
}
/**
* This method returns the trait of the animal
* @return the Trait
*/
public String getTrait() {
return trait;
}
/**
* This method returns the Age effect of the animal
* @return the Age Effect
*/
public String getAgeEffect() {
return ageEffect;
}
/**
* This method returns the happiness of the animal
* @return the happy stat
*/
public int getHappy() {
return happy;
}
/**
* This method returns the hungry statistic of the animal
* @return the hungry
*/
public int getHungry() {
return hungry;
}
/**
* This method returns the Energy statistic of the animal
* @return the energy
*/
public int getEnergy() {
return energy;
}
/**
* This method returns the Weight statistic of the animal
* @return the weight
*/
public int getWeight() {
return weight;
}
/**
* This method returns the Hygiene statistic of the animal
* @return the hygiene
*/
public int getHygiene() {
return hygiene;
}
/**
* This method returns the age of the animal
* @return the age
*/
public int getAge() {
return age;
}
/**
* This method returns the Thirst statistic of the animal
* @return the thirst
*/
public int getThirst()
{
return thirst;
}
/**
* This method it used to change the Name of the animal
* @param nName - the new name
*/
public void setName(String nName) {
name = nName;
}
public void setGender(Gender nGender)
{
gender = nGender;
}
/**
* This method it used to change the trait of the animal
* @param nTrait- the new trait of the animal
*/
public void setTrait(String nTrait) {
trait = nTrait;
}
/**
* This method it used to change the age effect of the animal
* @param nAgeEffect - the new age affect of the animal
*/
public void setAgeEffect(String nAgeEffect) {
ageEffect = nAgeEffect;
}
/**
* This method it used to change the happy statistic of the animal
* @param nHappy - the new happy statistic of the animal
*/
public void setHappy(int nHappy) {
happy = nHappy;
if (happy > 500) {happy = 500;}
if (happy < 0 ){happy = 0;}
}
/**
* This method it used to change the hungry statistic of the animal
* @param nHungry the new hungry statistic of the animal
*/
public void setHungry(int nHungry) {
hungry = nHungry;
if (hungry > 500) {hungry = 500;}
if (hungry < 0 ){hungry = 0;}
}
/**
* This method it used to change the happy statistic of the animal
* @param nEnergy- the new energy statistic of the animal.
*/
public void setEnergy(int nEnergy) {
energy = nEnergy;
if (energy > 500) {energy = 500;}
if (energy < 0 ){energy = 0;}
}
/**
* This method it used to change the Weight statistic of the animal
* @param nWeight - the new weight statistic of the animal
*/
public void setWeight(int nWeight) {
weight = nWeight;
}
/**
* This method it used to change the Hygiene statistic of the animal
* @param nHygiene - the new hygiene statistic of the animal
*/
public void setHygiene(int nHygiene) {
hygiene = nHygiene;
if (hygiene > 500) {hygiene = 500;}
if (hygiene < 0 ){hygiene = 0;}
}
/**
* This method it used to change the age of the animal
* @param nAge - the animals new age
*/
public void setAge(int nAge) {
age = nAge;
}
/**
* This method is used to change the thirst statistic of the animal
* @param nThirst - the animals new thirst statistic
*/
public void setThirst(int nThirst)
{
thirst = nThirst;
if (thirst > 500) {thirst = 500;}
if (thirst < 0 ){thirst = 0;}
}
/**
* This method will be used by the end user to interact with the animal.
* Playing with the animal will make it happy
*/
public void play()
{
happy = happy + 50;
energy = energy - 50;
weight = weight - 5;
}
/**
* This method will be used by the end user to interact with the animal.
* cleaning the animal will increase it's hygiene. but will make it more unhappy
*/
public void clean()
{
hygiene = hygiene + 50;
happy = happy - 25;
}
/**
* This method will be used by the end user to interact with the animal.
* Feeding the animal will make it less hungry
*/
public void feed()
{
System.out.println("You have fed " + name);
hungry = hungry + 50;
}
/**
* This method will be used by the end user to interact with the animal.
* Giving the animal a drink will increase the thirst variable.
*/
public void drink()
{
thirst = thirst + 50;
}
/**
* This method will be used by the end user to interact with the animal.
* Letting the animal sleep will increase it's energy
*/
public void sleep()
{
System.out.println(name + " is now sleeping");
energy = energy + 50;
}
/**
* This method will be called if the animal's energy drops below a certain level
* If an animal passes out it's energy will increase but it's happiness will decrease a lot
*/
public void passOut()
{
System.out.println(name + " has passed out from being to tired");
happy = happy - 50;
energy = energy + 25;
}
public void Death()
{
System.out.println("Your animal has now died");
}
public void runAway()
{
System.out.println("Your animal has run away because of you poor care");
}
}
主要方法：
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
public class CatInterface_Tester {
public static void main(String[] args) {
Cat_Interface myInterface = new Cat_Interface(null);}
}
最后，当我运行界面时，它给了我这个错误：
Exception in thread "main" java.lang.NullPointerException
at Cat_Interface.<init>(Cat_Interface.java:75)
答案 0 :(得分：2)
"The cat.getHappy() that I am referencing seems to pull up an error" - 请发布错误消息。就我们所知，你的cat变量可能为null，你可能会得到一个NullPointerException。 如，
public void setProgress(int progress) {
myProgressBar.setValue(progress);
}
修改
更好的答案是根据MadProgrammer - 尝试将您的GUI（也称为“视图”）与业务数据分开，使用模型 - 视图 - 控制类型的架构来分析您的“模型”。如果你走这条路线，你的视图将通过控件直接或间接地将监听器添加到模型中，以便在模型改变状态时通知它，然后它可以改变其数据的表示。这是一个更高级的编程概念，如果你刚刚开始，可能会过度杀戮，但它是有效的，当你需要调试你的应用程序或想要改进它时，它肯定有助于。
编辑2
您已验证您的例外是NPE。这是因为cat变量为null。解决方案：不要尝试在空变量上调用方法，而是首先尝试为其分配有效的引用。这可能很简单：
Cat cat = new Cat();
编辑3