私は長い間コーディングをしていませんが、これはこれまでに見た中で最も奇妙なエラーです。Null Pointer Exceptionエラーが表示されていることがわかりましたが、これは1週間以上Web上で見つけることができなかった特定のもので、2つ続いています。私は非常にユニークな問題に遭遇し、緊急に助けが必要です. (私は回避策を思いついたので、時間通りにプロジェクトを終了しますが、このエラーはまだ私を悩ませています)。（コードは質問の一番下にあります）。
プロジェクト: 信号機シミュレーションを作成するには:
- 開始時は「オフ」になっており、キーボードの「o」キーでオンにする必要があります。オフもできるはずです。
- 「f」キーを押すと、黄色のライトが点滅します。
- 実際の信号機の進行状況 (緑 > 黄 > 赤 > 緑 > など) が必要です。
問題: パネル メソッドで paintComponent(Graphics pen) が発生すると、そこから複数のエラーが生成されます。(スクリーンショット:エラー)
パネル内でオブジェクトが作成された後のいずれかの時点で発生すると推測しました (コードを読んだときに理解できます)。回避策は単純に、クラス メソッドから元のパネルに直接コピー アンド ペーストするだけなので、これは非常に特殊です。
つまり、私のコードが pen.drawOval(insert parameters) で Oval を描画する場合、それは paintComponent(Graphics pen) メソッドを保持する panel クラスで機能します。しかし、それがたとえば Circle クラスの場合は機能しません。
このエラーは、paintComponent が別のクラスのオブジェクト、別のクラスの変数、または別のクラスのメソッドにアクセスする場合にのみ生成されます。
Circle オブジェクトが使用された場合、object.drawOval(parameters) は機能しませんが、パネル内で別の public void メソッドが使用され、objectDraw(Graphics pen) と呼ばれ、paintComponent から objectDraw(pen) として実行された場合、それは機能します。 .
できる限り説明したことを願っています。
次に、領域を生成するコードについて説明します。
私は見落としているほど単純なものであるという気分が悪くなります。これがエラーを生成する理由を発見できなかったため、これは本当に私の最後の手段です。
(JComponent が破損することはありますか?それは単にユーザー固有のものでしょうか?)
コード：
ライトは、内部に複数のオブジェクトをプライベート クラスとして保持するグループ クラスと考えてください。（これは問題でしょうか、プライベートクラスですか？）
/******************
* Lights.java
*
* Creates graphic objects.
*
******************/
import java.awt.*; //Import the awt package.
public class Lights{ //Driver class header.
private final int RED = 1; //Creates switch constant.
private final int YELLOW = 2; //Creates switch constant.
private final int GREEN = 3; //Creates switch constant.
private final int ALL_ON = 5; //Creates switch constant.
private final int ALL_OFF = 6; //Creates switch constant.
private final int BACKGROUND = 0; //Background switch constant.
private final int FOREGROUND = 8; //Foreground switch constant.
private final int FLASHING_YELLOW = 4; //Creates Flashing Yellow
private final int DARK_YELLOW = 9; //Case in case.
private int flashingColor = YELLOW; //Case in case.
private boolean flashingYellow = false; //Creates false by default flashingYellow boolean.
private Color lightColor; //Color variable lightcolor.
private int colorSwitch; //Switch integer using constants and lightcolor.
private int typeSwitch; //Also similar to above.
private int x, y, lightswitch; //Other integers.
private Rectangle grayBG, blackBG;
private Circle red, green, yellow, redFore, greenFore, yellowFore;
public Lights(){
Rectangle grayBG = new Rectangle(35, 35, 280, 830, true);
Rectangle blackBG = new Rectangle(50, 50, 250, 800, true);
Circle red = new Circle(80, 75, 200, 200, true);
Circle green = new Circle(80, 575, 200, 200, true);
Circle yellow = new Circle(80, 325, 200, 200, true);
Circle redFore = new Circle(80, 75, 200, 200, false);
Circle greenFore = new Circle(80, 575, 200, 200, false);
Circle yellowFore = new Circle(80, 325, 200, 200, false);
}
//Drawn when flash is on.
public void flashOn(Graphics g){
drawYellowLight(g, true);
drawGreenLight(g, false);
drawRedLight(g, false);
drawFore(g);
}
//Drawn when light is off.
public void flashOff(Graphics g){
drawYellowLight(g, false);
drawGreenLight(g, false);
drawRedLight(g, false);
drawFore(g);
}
//Draws the foreground.
public void drawFore(Graphics pen){
drawRed(pen);
drawYellow(pen);
drawGreen(pen);
}
//Draws the foreground's red, yellow, and green.
public void drawRed(Graphics pen){
pen.setColor(Color.RED);
redFore.draw(pen);
}
public void drawYellow(Graphics pen){
pen.setColor(Color.YELLOW);
yellowFore.draw(pen);
}
public void drawGreen(Graphics pen){
pen.setColor(Color.GREEN);
greenFore.draw(pen);
}
//Draws the background.
public void drawBox(Graphics pen){
//HTML Color Code for 'LightYellow4' (looks gray though); Color GRAY = new Color(139, 139, 122);
pen.setColor(new Color(139, 139, 122));
grayBG.draw(pen);
pen.setColor(Color.BLACK);
blackBG.draw(pen);
}
//Draws the green light whether on or off.
public void drawGreenLight(Graphics pen, boolean isOn){
//Color darkGreen = new Color(105, 139, 105);
//Color lightGreen = new Color(0, 238, 0);
if(!isOn){
pen.setColor(new Color(105, 139, 105));
green.draw(pen);
} else {
pen.setColor(new Color(0, 238, 0));
green.draw(pen);
}
}
//Draws the yellow light whether on or off.
public void drawYellowLight(Graphics pen, boolean isOn){
//Color darkYellow = new Color(139, 69, 0);
//Color lightYellow = new Color(255, 215, 0);
if(!isOn){
pen.setColor(new Color(139, 69, 0));
yellow.draw(pen);
} else {
pen.setColor(new Color(255, 215, 0));
yellow.draw(pen);
}
}
//Draws the red light whether on or off.
public void drawRedLight(Graphics pen, boolean isOn){
//Color darkRed = new Color(139, 26, 26);
//Color lightRed = new Color(255, 48, 48);
if(!isOn){
pen.setColor(new Color(139, 26, 26));
red.draw(pen);
} else {
pen.setColor(new Color(255, 48, 48));
red.draw(pen);
}
}
/******************
* Lights$Rectangle.java
*
* Creates a graphic object named Rectangle.
*
******************/
private class Rectangle{ //Driver class header.
//Define global private integers.
private int x, y, h, w;
private boolean fill;
//Methods
//Object constructor, Definition.
//Defines the info for a rectangle.
public Rectangle(int a, int b, int height, int width, boolean isFilled){
x = a;
y = b;
h = height;
w = width;
fill = isFilled;
}
public void draw(Graphics pen){
if(fill == true){
int xPosition = x - w;
int yPosition = y - h;
pen.fillRect(xPosition, yPosition, w, h);
} else {
int xPosition = x - w;
int yPosition = y - h;
pen.drawRect(xPosition, yPosition, w, h);
}
}
}
/******************
* Lights$Circle.java
*
* Creates a graphic object named Rectangle.
*
******************/
private class Circle{
//Define global private integers.
private int x, y, radius;
private boolean fill;
//Object constructor, Definition.
//Defines the info for a circle.
public Circle(int a, int b, int size, int size_alt, boolean isFilled){
x = a;
y = b;
radius = ((int)size/2);
fill = isFilled;
}
public void draw(Graphics pen){
if(fill == true){
int diameter = (radius*2);
int xPosition = x - radius;
int yPosition = y - radius;
pen.fillOval(xPosition, yPosition, diameter, diameter);
} else {
int diameter = (radius*2);
int xPosition = x - radius;
int yPosition = y - radius;
pen.drawOval(xPosition, yPosition, diameter, diameter);
}
}
}
}
今度はフレームクラスです。コード：
Traffic.java は、このプロジェクトの文字通りの JFrame ピースです。
/****************************
* Traffic.java
*
*
******************************/
import javax.swing.*; //Import swing package.
import java.awt.*; //Import awt package.
import java.awt.event.*; //Import events package.
public class Traffic extends JFrame{
public static void main(String[] args){
//Create new JFrame.
JFrame lightbox = new JFrame("Light Box");
//Create new LightboxPanel.
TrafficPanel traffic = new TrafficPanel();
//Set focus to the LightboxPanel in order to allow key inputs.
traffic.setFocusable(true);
//Set the Default Close Operation to exit when the "x" button is selected.
lightbox.setDefaultCloseOperation(EXIT_ON_CLOSE);
//Add the LightboxPanel to the Lightbox JFrame.
lightbox.add(traffic);
//Pack the frame to the warranted preferred size of the LightboxPanel.
lightbox.pack();
//Set the frame's visibility to true.
lightbox.setVisible(true);
}
}
最後に、パネル クラス自体である TrafficPanel.java は、Lights からグラフィックスをペイントするメソッドを呼び出すパネルです。
コード：
//*****************************************************************************
// TrafficPanel.java
//
// Panel that holds graphics for the traffic light simulation.
//*****************************************************************************
import java.util.Scanner; // import Scanner class from util package
import javax.swing.JPanel; // import JPanel class from swing package
import javax.swing.JButton;
import java.awt.*; // import awt package
import java.awt.event.*; // import event package from awt package
import java.util.Random; // import Random class from the util package
public class TrafficPanel extends JPanel
{
private Lights shapes;
private final int RED = 1; //Creates switch constant.
private final int YELLOW = 2; //Creates switch constant.
private final int GREEN = 3; //Creates switch constant.
private final int ALL_ON = 5; //Creates switch constant.
private final int ALL_OFF = 6; //Creates switch constant.
private final int FLASHING_YELLOW = 4; //Creates Flashing Yellow
private final int DARK_YELLOW = 9; //Case in case.
private int flashingColor = YELLOW; //Case in case.
private boolean flashingYellow = false; //Creates false by default flashingYellow boolean.
private Color lightColor; //Color variable lightcolor.
private int colorSwitch; //Switch integer using constants and lightcolor.
private int typeSwitch; //Also similar to above.
private int x, y, lightswitch; //Other integers.
public TrafficPanel()
{
Lights shapes = new Lights();
//KeyListener trafficListener = new KeyListener();
addKeyListener(new KeyListener());
//Set the size.
//Dimension preferred = new Dimension(800, 920);
setPreferredSize(new Dimension(800, 920));
//Set the background.
//Color bisque = new Color(255, 228, 196);
setBackground(new Color(255, 228, 196));
}
public void paintComponent (Graphics g)
{
super.paintComponent (g);
//Normal state of panel. Initially offline.
Lights shapes = new Lights();
shapes.drawBox(g);
shapes.drawRedLight(g, false);
shapes.drawYellowLight(g, false);
shapes.drawGreenLight(g, false);
shapes.drawFore(g);
//Check state of light.
switch(lightswitch){
case ALL_OFF:
shapes.drawBox(g);
shapes.drawRedLight(g, false);
shapes.drawYellowLight(g, false);
shapes.drawGreenLight(g, false);
shapes.drawFore(g);
break;
case ALL_ON:
shapes.drawBox(g);
shapes.drawRedLight(g, true);
shapes.drawYellowLight(g, true);
shapes.drawGreenLight(g, true);
shapes.drawFore(g);
break;
case RED:
shapes.drawBox(g);
shapes.drawRedLight(g, true);
shapes.drawYellowLight(g, false);
shapes.drawGreenLight(g, false);
shapes.drawFore(g);
break;
case GREEN:
shapes.drawBox(g);
shapes.drawRedLight(g, false);
shapes.drawYellowLight(g, false);
shapes.drawGreenLight(g, true);
shapes.drawFore(g);
break;
case YELLOW:
shapes.drawBox(g);
shapes.drawRedLight(g, false);
shapes.drawYellowLight(g, true);
shapes.drawGreenLight(g, false);
shapes.drawFore(g);
break;
case FLASHING_YELLOW: //If Flashing yellow.
switch(flashingColor){
case DARK_YELLOW:
flashingColor = YELLOW;
break;
case YELLOW:
flashingColor = DARK_YELLOW;
break;
}
try{
if(flashingColor == YELLOW){
shapes.flashOn(g);
}
Thread.sleep(250);
if(flashingColor == DARK_YELLOW){
shapes.flashOff(g);
}
} catch(Exception e){}
break;
}
repaint ();
}
/*********************
* TrafficPanel$KeyListener.java
* Author: Ian Effendi
*
* Extension of KeyAdapter.
* Inputs of 'o', 'f', and the spacebar all return actions.
**********************/
private class KeyListener extends KeyAdapter{
//Occurs when a key is pressed.
public void keyPressed(KeyEvent event){
}
//Occurs, only, when a key is released.
public void keyReleased(KeyEvent event){
//If the key input is 'o'.
if(event.getKeyCode() == KeyEvent.VK_O){
flashingYellow = false;
//Switch on what lightswitch is equal to.
switch(lightswitch){
case ALL_ON:
lightswitch = ALL_OFF;
break;
case ALL_OFF:
lightswitch = ALL_ON;
break;
case RED:
lightswitch = ALL_OFF;
break;
case YELLOW:
lightswitch = ALL_OFF;
break;
case GREEN:
lightswitch = ALL_OFF;
break;
case FLASHING_YELLOW:
lightswitch = ALL_OFF;
break;
}
//If the key input is the spacebar.
} else if(event.getKeyCode() == KeyEvent.VK_SPACE){
flashingYellow = false;
//Switch on what lightswitch is equal to.
switch(lightswitch){
case ALL_ON:
lightswitch = RED;
break;
case ALL_OFF:
lightswitch = ALL_OFF;
break;
case RED:
lightswitch = GREEN;
break;
case YELLOW:
lightswitch = RED;
break;
case GREEN:
lightswitch = YELLOW;
break;
case FLASHING_YELLOW:
lightswitch = YELLOW;
break;
}
//If the key input is 'f'.
} else if(event.getKeyCode() == KeyEvent.VK_F){
flashingYellow = true;
//Switch on what lightswitch is equal to.
switch(lightswitch){
case ALL_ON:
lightswitch = FLASHING_YELLOW;
break;
case ALL_OFF:
lightswitch = ALL_OFF;
break;
case RED:
lightswitch = FLASHING_YELLOW;
break;
case YELLOW:
lightswitch = FLASHING_YELLOW;
break;
case GREEN:
lightswitch = FLASHING_YELLOW;
break;
case FLASHING_YELLOW:
lightswitch = YELLOW;
break;
}
//If nothing is input, lightswitch returns itself.
} else {
int x = lightswitch;
lightswitch = x;
}
}
//Occurs when an input is typed(not held).
public void keyTyped(KeyEvent event){
}
}
}//end of class
それがすべてのコードです。できる限り助けてください。ヒントもいただければ幸いです。