NullPointerException异常的二维数组 [英] NullPointerException in 2D array
本文介绍了NullPointerException异常的二维数组的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我写了这个code（自包含），它抛出了我的困惑NPE。它涉及雷在模型中使用对象的二维数组。在雷对象初始化并设置模型。当他们需要在模型外，在code调用 model.getRays（）。在这一点上code遍历二维数组和放大器;日志的每个对象，因为..区区2-3线code来电之后 getRays（），二维数组的第一个元素是空！
有没有线程发生可能与数组中的物体干扰，所以我困惑至于他们如何能够空只测试后的时刻，它们包含有效对象。
什么是错的这个code＆放;我该如何解决这个问题？
进口java.awt中的*。
进口java.awt.event.ActionEvent中;
导入的java.awt.geom *。
进口java.awt.image.BufferedImage中;
导入java.util.logging的*。
进口的javax.swing *。
进口javax.swing.border.EmptyBorder中;公共类TestNullOn2DArray { 公共静态无效的主要（字串[] args）{
可运行R =新的Runnable（）{ @覆盖
公共无效的run（）{
桂=新的GUI（）; JFrame的F =新的JFrame（测试空二维阵列）;
f.add（gui.getContainer（））;
f.setDefaultCloseOperation（JFrame.DISPOSE_ON_CLOSE）;
f.setLocationByPlatform（真）; f.pack（）;
f.setMinimumSize（f.getSize（））;
f.setVisible（真）;
gui.plot（）;
}
};
SwingUtilities.invokeLater（R）;
}
}类GUI { 记录器记录= Logger.getAnonymousLogger（）;
私人的JPanel容器;
JLabel的输出;
私人的JMenuBar菜单栏;
私人的BufferedImage帆布;
私人CustomModel模型=
新CustomModel（5,1，.66f）;
私人INT defaultPositionNumber = 5;
私人INT defaultAngleNumber = 5; 公共无效情节（）{
射线[] []光线= model.getRays（）;
log.log（Level.INFO，霞光：+射线）;
为（中间体二= 0; II蛋白酶rays.length;ⅱ++）{
对于（INT JJ = 0; JJ＆LT;光线[II]。长度; JJ ++）{
一缕一缕光线= [II] [林俊杰];
log.log（Level.INFO，雷：+射线）;
ray.resolve（）;
}
}
} 公众的JPanel getContainer（）{
如果（集装箱== NULL）{
集装箱=新JPanel（新的BorderLayout（5,5））;
container.setBorder（新EmptyBorder（4,4，4,4））; ImageIcon的图标=新的ImageIcon（getCanvas（））;
输出=新的JLabel（图标）;
container.add（新JScrollPane的（输出），BorderLayout.CENTER）;
}
返回容器中;
} 公共无效refreshCanvas（）{
模型=新CustomModel（5,6，.66f）;
帆布= NULL;
BufferedImage的BI = getCanvas（）;
output.setIcon（新的ImageIcon（BI））;
} 公共无效initializeRays（Graphics2D的G）{
log.log（Level.INFOinitializeRays（））; INT由startAngle = 1;
INT numberAngles = defaultAngleNumber;
INT INC = 90 / numberAngles;
INT numberPositions = defaultPositionNumber;
雷[] [] =光线雷新[numberAngles] [numberPositions];
g.setTransform（AffineTransform.getTranslateInstance（0D，0D））;
为（中间体二= rays.length - 1;ⅱ大于0; ii--）{
对于（INT JJ = 0; JJ＆LT;光线[0]。长度; JJ ++）{
GP的GeneralPath =新GeneralPath（）; 双拉德= 2D * Math.PI *（由startAngle +（INC * II））/ 360D;
双X = 400D;
双Y = 100D;
双yStart = Y - （Math.sin（拉德）* 100D）;
双XSTART = X +（Math.cos（拉德）* 100D）;
浮R = 2F *（浮点）（（拉德/ Math.PI））;
浮动B =（浮点）JJ /（浮点）射线[0]。长度;
色色=新的色彩（R，1 - R，B，.6f）;
g.setColor（颜色）;
g.drawLine（（INT）X，（INT）Y（INT）XSTART，（INT）yStart）;
gp.moveTo（XSTART，yStart）;
gp.lineTo（X，Y）;
gp.closePath（）;
一缕一缕=新雷（GP，颜色）;
log.log（Level.INFO，+射线）;
光线[II] [林俊杰] =射线;
}
}
model.setRays（线）;
如果（输出！= NULL）{
output.repaint（）;
}
} 公众的BufferedImage getCanvas（）{
如果（帆布== NULL）{
尺寸大小= model.get preferredSize（）;
INT W = size.width;
INT H = size.height;
帆布=新的BufferedImage（W，H，BufferedImage.TYPE_INT_ARGB）;
Graphics2D的G = canvas.createGraphics（）; g.setColor（Color.WHITE）;
g.fillRect（0，0，W，H）;
g.setColor（新颜色（125，27，155，127））; initializeRays（G）; g.dispose（）;
}
返回帆布;
}
}类CustomModel { 私人诠释宽度;
私人诠释层;
私人浮动抵消;
私人雷[] []照射;
私人记录器记录= Logger.getAnonymousLogger（）; 公共CustomModel（INT宽度，诠释层，浮偏移）{
this.width =宽度;
this.layers =层;
this.offset =偏移;
} 公共Line2D.Double getLineOfLasSegment（）{
Line2D.Double行=新Line2D.Double（0D，0D，1D，1D）;
回线;
} 公共尺寸的get preferredSize（）{
INT W = 600;
INT H = 300;
尺寸prefSize =新尺寸（W，H）;
返回prefSize;
} 公众诠释的getWidth（）{
返回宽度;
} 公共无效setWidth（int width）将{
this.width =宽度;
} 公众诠释getLayers（）{
返回层;
} 公共无效setLayers（INT层）{
this.layers =层;
} 公共雷[] [] getRays（）{
为（中间体二= 0; II蛋白酶rays.length;ⅱ++）{
对于（INT JJ = 0; JJ＆LT;光线[II]。长度; JJ ++）{
log.log（Level.INFO，雷：+ this.rays [II] [林俊杰]）;
}
}
返回光线;
} 公共无效setRays（雷[] []射线）{
this.rays =光线;
为（中间体二= 0; II蛋白酶rays.length;ⅱ++）{
对于（INT JJ = 0; JJ＆LT;光线[II]。长度; JJ ++）{
//一缕一缕光线= [II] [林俊杰];
this.rays [II] [JJ] =射线[II] [JJ];
log.log（Level.INFO，雷：+ this.rays [II] [林俊杰]）;
}
}
} 公众持股量的getOffset（）{
返回偏移;
} 公共无效setOffset（浮点偏移）{
this.offset =偏移;
}
}雷类{ 私人最终记录器记录= Logger.getAnonymousLogger（）;
私人的GeneralPath路径;
私人布尔开始= FALSE;
私人色彩的颜色; 雷（的GeneralPath路径，色色）{
this.path =路径;
this.color =颜色;
} 公共无效解析（）{
logger.log（Level.INFO..resolving。）;
} 公众的GeneralPath的getPath（）{
返回路径;
} 公共布尔isStarted（）{
返回开始;
} @覆盖
公共字符串的toString（）{
字符串s =雷
+开始=+启动;
返回S;
}
}
输出
这显示输出的最后部分检查什么 getRays（）将返回，随后NPE。
// ...
2013年6月29日下午4时56分55秒CustomModel getRays
INFO：雷：雷：开始= FALSE
2013年6月29日下午4时56分55秒的GUI情节
INFO：光芒：[LRay; @ 1a9876e
2013年6月29日下午4时56分55秒的GUI情节
INFO：雷：空
在异常线程AWT-EventQueue的-0显示java.lang.NullPointerException
在GUI.plot（TestNullOn2DArray.java:52）
在TestNullOn2DArray $ 1.run（TestNullOn2DArray.java:26）
在java.awt.event.InvocationEvent.dispatch（InvocationEvent.java:251）
在java.awt.EventQueue.dispatchEventImpl（EventQueue.java:727）
在java.awt.EventQueue.access $ 200（EventQueue.java:103）
在java.awt.EventQueue中的$ 3.run（EventQueue.java:688）
在java.awt.EventQueue中的$ 3.run（EventQueue.java:686）
在java.security.AccessController.doPrivileged（本机方法）
在java.security.ProtectionDomain $ 1.doIntersectionPrivilege（ProtectionDomain.java:76）
在java.awt.EventQueue.dispatchEvent（EventQueue.java:697）
在java.awt.EventDispatchThread.pumpOneEventForFilters（EventDispatchThread.java:242）
在java.awt.EventDispatchThread.pumpEventsForFilter（EventDispatchThread.java:161）
在java.awt.EventDispatchThread.pumpEventsForHierarchy（EventDispatchThread.java:150）
在java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:146）
...
解决方案
通过我的调试器看着它，它看起来好像一切在射线[0] 为空。一切的其他的是present。
这样，通过跟踪挖掘，相信已经发现的数据摆在首位，，并把那里的原因的原因第一行是空的：
-
我们称之为
f.add（gui.getContainer（））;。这似乎无伤大雅在其本身，而是让我们看看getContainer正在做... -
我们实例化
ImageIcon的图标=新的ImageIcon（getCanvas（））;。再次，无伤大雅，但让我们再次下井兔子洞... -
我们再调用（最终）
initializeRays（G）;在getCanvas（）！发生了什么事错在这里？ 此：的for（int II = rays.length - 1;二大于0;二 - ）
好吧，你计算的向后的。怪异，并且只能在极少数情况下做到的，但我想你有你的理由。但是，有两个卡口向后计数：
- 您需要长度为n-1，你做启动;和
- 您的循环条件必须比的或等于的0，你的不的有状态。 更大
将其更改为包括大于或等于-进行测试，你不会有任何更多的NPE。
I have written this code (self contained) which throws an NPE that has me confounded. It involves a 2D array of Ray objects used in a model. The Ray objects are initialized and set to the model. When they are required outside the model, the code calls model.getRays(). At that point the code iterates the 2D array & logs each object, because.. A mere 2-3 lines after the code calls getRays(), the first element of the 2D array is null!
There are no threads happening that might interfere with the objects in the array, so I am confounded as to how they could be null only moments after testing that they contain valid objects.
What is wrong with this code & how do I fix it?
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.util.logging.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
public class TestNullOn2DArray {
public static void main(String[] args) {
Runnable r = new Runnable() {
@Override
public void run() {
GUI gui = new GUI();
JFrame f = new JFrame("Test Null On 2D Array");
f.add(gui.getContainer());
f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
f.setLocationByPlatform(true);
f.pack();
f.setMinimumSize(f.getSize());
f.setVisible(true);
gui.plot();
}
};
SwingUtilities.invokeLater(r);
}
}
class GUI {
Logger log = Logger.getAnonymousLogger();
private JPanel container;
JLabel output;
private JMenuBar menuBar;
private BufferedImage canvas;
private CustomModel model =
new CustomModel(5, 1, .66f);
private int defaultPositionNumber = 5;
private int defaultAngleNumber = 5;
public void plot() {
Ray[][] rays = model.getRays();
log.log(Level.INFO, "Rays: " + rays);
for (int ii = 0; ii < rays.length; ii++) {
for (int jj = 0; jj < rays[ii].length; jj++) {
Ray ray = rays[ii][jj];
log.log(Level.INFO, "Ray: " + ray);
ray.resolve();
}
}
}
public JPanel getContainer() {
if (container == null) {
container = new JPanel(new BorderLayout(5, 5));
container.setBorder(new EmptyBorder(4, 4, 4, 4));
ImageIcon icon = new ImageIcon(getCanvas());
output = new JLabel(icon);
container.add(new JScrollPane(output), BorderLayout.CENTER);
}
return container;
}
public void refreshCanvas() {
model = new CustomModel(5, 6, .66f);
canvas = null;
BufferedImage bi = getCanvas();
output.setIcon(new ImageIcon(bi));
}
public void initializeRays(Graphics2D g) {
log.log(Level.INFO, "initializeRays()");
int startAngle = 1;
int numberAngles = defaultAngleNumber;
int inc = 90 / numberAngles;
int numberPositions = defaultPositionNumber;
Ray[][] rays = new Ray[numberAngles][numberPositions];
g.setTransform(AffineTransform.getTranslateInstance(0d, 0d));
for (int ii = rays.length - 1; ii > 0; ii--) {
for (int jj = 0; jj < rays[0].length; jj++) {
GeneralPath gp = new GeneralPath();
double rads = 2d * Math.PI * (startAngle + (inc * ii)) / 360d;
double x = 400d;
double y = 100d;
double yStart = y - (Math.sin(rads) * 100d);
double xStart = x + (Math.cos(rads) * 100d);
float r = 2f * (float) ((rads / Math.PI));
float b = (float) jj / (float) rays[0].length;
Color color = new Color(r, 1 - r, b, .6f);
g.setColor(color);
g.drawLine((int) x, (int) y, (int) xStart, (int) yStart);
gp.moveTo(xStart, yStart);
gp.lineTo(x, y);
gp.closePath();
Ray ray = new Ray(gp, color);
log.log(Level.INFO, "" + ray);
rays[ii][jj] = ray;
}
}
model.setRays(rays);
if (output != null) {
output.repaint();
}
}
public BufferedImage getCanvas() {
if (canvas == null) {
Dimension size = model.getPreferredSize();
int w = size.width;
int h = size.height;
canvas = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
Graphics2D g = canvas.createGraphics();
g.setColor(Color.WHITE);
g.fillRect(0, 0, w, h);
g.setColor(new Color(125, 27, 155, 127));
initializeRays(g);
g.dispose();
}
return canvas;
}
}
class CustomModel {
private int width;
private int layers;
private float offset;
private Ray[][] rays;
private Logger log = Logger.getAnonymousLogger();
public CustomModel(int width, int layers, float offset) {
this.width = width;
this.layers = layers;
this.offset = offset;
}
public Line2D.Double getLineOfLasSegment() {
Line2D.Double line = new Line2D.Double(0d, 0d, 1d, 1d);
return line;
}
public Dimension getPreferredSize() {
int w = 600;
int h = 300;
Dimension prefSize = new Dimension(w, h);
return prefSize;
}
public int getWidth() {
return width;
}
public void setWidth(int width) {
this.width = width;
}
public int getLayers() {
return layers;
}
public void setLayers(int layers) {
this.layers = layers;
}
public Ray[][] getRays() {
for (int ii = 0; ii < rays.length; ii++) {
for (int jj = 0; jj < rays[ii].length; jj++) {
log.log(Level.INFO, "Ray: " + this.rays[ii][jj]);
}
}
return rays;
}
public void setRays(Ray[][] rays) {
this.rays = rays;
for (int ii = 0; ii < rays.length; ii++) {
for (int jj = 0; jj < rays[ii].length; jj++) {
//Ray ray = rays[ii][jj];
this.rays[ii][jj] = rays[ii][jj];
log.log(Level.INFO, "Ray: " + this.rays[ii][jj]);
}
}
}
public float getOffset() {
return offset;
}
public void setOffset(float offset) {
this.offset = offset;
}
}
class Ray {
private final Logger logger = Logger.getAnonymousLogger();
private GeneralPath path;
private boolean started = false;
private Color color;
Ray(GeneralPath path, Color color) {
this.path = path;
this.color = color;
}
public void resolve() {
logger.log(Level.INFO, "..resolving.");
}
public GeneralPath getPath() {
return path;
}
public boolean isStarted() {
return started;
}
@Override
public String toString() {
String s = "Ray: "
+ " started=" + started;
return s;
}
}
Output
This shows the last part of the output checking what getRays() will return, followed by the NPE.
// ...
Jun 29, 2013 4:56:55 PM CustomModel getRays
INFO: Ray: Ray: started=false
Jun 29, 2013 4:56:55 PM GUI plot
INFO: Rays: [[LRay;@1a9876e
Jun 29, 2013 4:56:55 PM GUI plot
INFO: Ray: null
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at GUI.plot(TestNullOn2DArray.java:52)
at TestNullOn2DArray$1.run(TestNullOn2DArray.java:26)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:727)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:697)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
...
解决方案
Looking at it through my debugger, it looks like everything at ray[0] is null. Everything else is present.
So, digging through the trace, I believe to have found the reason that data is put there in the first place, and why the first row is empty:
We call
f.add(gui.getContainer());. This seem innocuous in and of itself, but let's see whatgetContaineris doing...We instantiate
ImageIcon icon = new ImageIcon(getCanvas());. Again, innocuous, but let's go down the rabbit hole again...We then call (finally)
initializeRays(g);ingetCanvas()! What's going wrong here? This:for (int ii = rays.length - 1; ii > 0; ii--)
Okay, you're counting backwards. Weird, and only should be done in rare cases, but I suppose you have your reasons. But, there's two catches to counting backwards:
- You need to start at length n-1, which you do; and
- Your loop condition must be greater than or equal to 0. You do not have that condition.
Change it to include the greater-than or equal-to test, and you will not have any more NPEs.
这篇关于NullPointerException异常的二维数组的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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