[英]Java Object values not consistent
我找不到其他解决方案,因为我不确定如何用足够多的词来描述它。
当我分配activeList
,这是一个字段currentActiveList
在随机生成的矩形ActiveList
其接收的值就好类。
public class ActiveList {
Rectangle[] activeList = new Rectangle[10];
public ActiveList() {
for(int i = 0; i < activeList.length; i++)
activeList[i] = null;
}
public void addToList(Rectangle x) {
for(int i = 0; i < this.activeList.length; i++) {
if(this.activeList[i] == null) {
this.activeList[i] = x;
i = this.activeList.length+1;
}
else
this.activeList[activeList.length-1] = x;
}
}
public Rectangle[] getActiveList() {
return this.activeList;
}
public int getLength() {
//System.out.print(this.activeList.length);
return this.activeList.length;
}
public void deleteFromList(int x) {
this.activeList[x] = null;
}
public Rectangle getFromList(int x) {
Rectangle retVal = this.activeList[x];
//System.out.println("Returning getFromList(int x): " +retVal);
return retVal;
}
public void genRandomRectangle() {
Random randomNumberGenerator = new Random();
double[] pointVal = new double[4];
double randomInt = randomNumberGenerator.nextInt(400-10);
pointVal[0] = randomInt;
randomInt = randomNumberGenerator.nextInt(400-10);
pointVal[1] = randomInt;
randomInt = randomNumberGenerator.nextInt((int) (400-pointVal[0]));
if(randomInt < 5) {
randomInt = randomInt+pointVal[0]+5;
}
else
pointVal[2] = randomInt+pointVal[0];
randomInt = randomNumberGenerator.nextInt((int) (400-pointVal[1]));
if(randomInt < 5) {
randomInt = randomInt+pointVal[1]+5;
}
else
pointVal[3] = randomInt+pointVal[1];
Rectangle newRandom = new Rectangle(pointVal[0], pointVal[1], pointVal[2], pointVal[3]);
//System.out.println(pointVal[0]);
//System.out.println(pointVal[1]);
//System.out.println(pointVal[2]);
//System.out.println(pointVal[3]);
System.out.println("New Random: " +newRandom);
addToList(newRandom);
}
}
然而,当我尝试在我的主类中使用这些值GraphicGen
,该currentActiveList
对所有的索引返回空值。
public class GraphicGen extends JPanel {
ActiveList currentActiveList = new ActiveList();
public static int gridSpaceX = 400;
public static int gridSpaceY = 400;
static JFrame mainFrame = new JFrame();
protected void paintComponent(Graphics g) {
//super.paintComponent(g);
Graphics2D g2 = (Graphics2D)g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
//int w = getWidth();
//int h = getHeight();
// Draw ordinate.
//g2.draw(new Line2D.Double(PAD, PAD, PAD, h-PAD));
// Draw abcissa.
//g2.draw(new Line2D.Double(PAD, h-PAD, w-PAD, h-PAD));
//double xInc = (double)(w - 2*PAD)/(data.length-1);
//double scale = (double)(h - 2*PAD)/maxValue();
// Mark data points.
//g2.setPaint(Color.red);
double[] coords = new double[4];
//g2.fill(new Ellipse2D.Double(coords[0], coords[1], 4, 4));
//g2.fill(new Ellipse2D.Double(coords[2], coords[3], 4, 4));
//g2.fill(new Ellipse2D.Double(100, 100, 4, 4));
System.out.println("Graphic Gen Active List Obj: " +currentActiveList);
System.out.println("Ya drew a new Main GUI!");
System.out.println("currentActiveList.getActiveList(): " +currentActiveList.getActiveList());
for(int i = 0; i < currentActiveList.getLength(); i++) {
//System.out.println("currentActiveList.getFromList(i): "+currentActiveList.getFromList(i));
//System.out.println("Graphic Gen Active List Obj: " +currentActiveList);
//System.out.println(activeList.getFromList(i).getTopLeftX());
if(currentActiveList.getFromList(i) != null) {
coords[0] = currentActiveList.getFromList(i).getTopLeftX();
System.out.println(coords[0]);
coords[1] = currentActiveList.getFromList(i).getTopLeftY();
System.out.println(coords[1]);
coords[2] = currentActiveList.getFromList(i).getBottomRightX();
System.out.println(coords[2]);
coords[3] = currentActiveList.getFromList(i).getBottomRightY();
System.out.println(coords[3]);
g2.draw(new Line2D.Double(coords[0], coords[1], coords[2], coords[1]));
g2.draw(new Line2D.Double(coords[0], coords[1], coords[0], coords[3]));
g2.draw(new Line2D.Double(coords[2], coords[1], coords[2], coords[3]));
g2.draw(new Line2D.Double(coords[0], coords[3], coords[2], coords[3]));
}
}
/*double x = 50;
double y = 50;
g2.fill(new Ellipse2D.Double(x, y, 4, 4));*/
/*for(int i = 0; i < data.length; i++) {
double x = PAD + i*xInc;
double y = h - PAD - scale*data[i];
g2.fill(new Ellipse2D.Double(x-2, y-2, 4, 4));
}*/
}
/*private int maxValue() {
int max = data[0];
for(int i = 0; i < data.length; i++) {
if(data[i] > max)
max = data[i];
}
return max;
}*/
public void callRepaintOnMain() {
mainFrame.repaint();
}
public void callGenRandom() {
currentActiveList.genRandomRectangle();
}
public static void main(String[] args) {
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
mainFrame.add(new GraphicGen());
mainFrame.setSize(gridSpaceX, gridSpaceY);
ButtonPrompt buttonPrompter = new ButtonPrompt();
mainFrame.setLocation(200,200);
mainFrame.setVisible(true);
}
}
动作生成器将调用随机生成器方法。
public class ButtonPrompt extends GraphicGen {
ActionListener actionListenerRandom = new ActionListener() {
public void actionPerformed(ActionEvent actionEvent) {
//currentActiveList.genRandomRectangle();
callGenRandom();
callRepaintOnMain();
}
};
JButton randomBtn = new JButton("Add Random Rectangle");
JButton inputCoordinates = new JButton("Input Rectangle Coordinates");
public ButtonPrompt() {
JFrame f = new JFrame("Add Rectangles");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
BoxLayout boxLayout = new BoxLayout(f.getContentPane(), BoxLayout.Y_AXIS);
f.setLayout(boxLayout);
randomBtn.addActionListener(actionListenerRandom);
f.setSize(200, 200);
f.setLocation(600, 200);
f.setVisible(true);
f.add(randomBtn);
f.add(inputCoordinates);
f.pack();
}
}
这是范围界定或引用问题吗? 我真的很茫然。
您的实际问题还不清楚,但是仅阅读前两种方法就足以发现我认为是一个错误:
public ActiveList() {
for(int i = 0; i < activeList.length; i++)
activeList[i] = null;
}
上面的代码完全没用。 对象数组的元素的默认值为null。 因此,循环将null分配给已经为null的变量。
public void addToList(Rectangle x) {
for(int i = 0; i < this.activeList.length; i++) {
if(this.activeList[i] == null) {
this.activeList[i] = x;
i = this.activeList.length+1;
}
else
this.activeList[activeList.length-1] = x;
}
}
如果列表仅包含null,则矩形将存储在索引0处,并且循环将停止。 对于此方法的所有后续调用,循环将发现索引0处的元素不为null,因此将x存储在数组的最后一个索引处,然后存储在第一个非null索引处。
我不确切地知道您要实现的目标以及实际的问题是什么,但是您可能应该忘记基于数组来实现自己的列表,而应该使用ArrayList。
这里:
public static void main(String[] args) {
...
mainFrame.add(new GraphicGen());
...
ButtonPrompt buttonPrompter = new ButtonPrompt();
}
ButtonPrompt
扩展了 GraphicGen
,它是一个JPanel
。 在ButtonPrompt
的构造函数中,您创建了一个JFrame
并向其中添加了两个JButton
。
因此,当您的应用程序启动时,屏幕上将有两个JFrame,一个是mainFrame
,其中包含一个GraphicGen
,另一个是buttonPrompter
,其中包含两个按钮。
当您单击按钮时,会调用actionPerformed()
,并且实际上是在调用buttonPrompter
的callGenRandom()
- 如果随机生成逻辑正确,则将生成的矩形添加到buttonPrompter
。 但是您没有将此buttonPrompter
添加到任何一个JFrame
,您将看不到它。
您可能想要什么:
ButtonPrompt
不延长GraphicGen
,而是给ButtonPrompt
的的参考GraphicGen
您添加到mainFrame
。
public class ButtonPrompt extends GraphicGen {
JButton randomBtn = new JButton("Add Random Rectangle");
JButton inputCoordinates = new JButton("Input Rectangle Coordinates");
final GraphicGen gg;
public ButtonPrompt(GraphicGen gg) {
this.gg = gg;
......
ActionListener actionListenerRandom = new ActionListener() {
public void actionPerformed(ActionEvent actionEvent) {
gg.callGenRandom();
gg.callRepaintOnMain();
}
};
randomBtn.addActionListener(actionListenerRandom);
......
}
}
并在您的main()
:
public static void main(String[] args) {
...
GraphicGen gg = new GraphicGen();
mainFrame.add(gg);
...
ButtonPrompt buttonPrompter = new ButtonPrompt(gg);
}
而且,代码还有其他问题。
例如, GraphicGen
是JPanel
主类,它具有JFrame
的字段,该字段实际上在应用程序运行时包含GraphicGen
实例-这看起来很糟。 我对Swing不太了解...是否必须调用包含JFrame
的repaint()
而不是仅调用JPanel
的repaint()
(如果有)?
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