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我開始一個非常簡單的java程序。用戶可以從菜單中選擇形狀，大小，填充（布爾），lineColor和fillColor，然後單擊並拖動以在屏幕上繪製選定的對象。在這一點上，我只是想弄清楚爲什麼沒有畫在屏幕上。在run方法中，我有一個以200,200繪製的簡單矩形，但面板上沒有任何東西出現。我相信，我可以讓程序的其餘部分工作得很好，一旦我找出爲什麼沒有繪畫任何想法我做錯了什麼？Java圖形繪製不顯示在繪圖面板上
import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import java.util.*;
import java.io.*;
import java.lang.*;
import java.awt.Rectangle;
public class E3G04 extends Frame implements WindowListener, ActionListener, ItemListener, MouseListener, MouseMotionListener, Runnable
{
volatile String type = "rectangle";
volatile Boolean fill = true;
Color lineColor = Color.BLACK;
Color fillColor = Color.BLACK;
int size = 1;
private Graphics obj;
Point start = new Point(100,100);
Point cur = new Point(100,100);
Point end = new Point(100,100);
Panel drawingpanel;
Thread thread = new Thread(this);
boolean running = true;
MenuBar mb = new MenuBar();
Menu fileMenu = new Menu("File");
MenuItem newItem = new MenuItem("New (Ctrl-N)");
MenuItem quitItem = new MenuItem ("Quit (Ctrl-Q)");
Menu drawMenu = new Menu("Draw");
Menu typeMenu = new Menu("Type");
CheckboxMenuItem ovalItem = new CheckboxMenuItem("Oval (Ctrl-O)");
CheckboxMenuItem rectItem = new CheckboxMenuItem("Rectangle (Ctrl-R)", true);
CheckboxMenuItem lineItem = new CheckboxMenuItem("Line (Ctrl-L)");
Menu fillMenu = new Menu ("Fill");
CheckboxMenuItem fillItem = new CheckboxMenuItem("Fill", true);
CheckboxMenuItem noFillItem = new CheckboxMenuItem("No Fill");
Menu colorMenu = new Menu ("Color");
CheckboxMenuItem blackLineItem = new CheckboxMenuItem("Black Line", true);
CheckboxMenuItem redLineItem = new CheckboxMenuItem("Red Line");
CheckboxMenuItem orangeLineItem = new CheckboxMenuItem("Orange Line");
CheckboxMenuItem yellowLineItem = new CheckboxMenuItem("Yellow Line");
CheckboxMenuItem greenLineItem = new CheckboxMenuItem("Green Line");
CheckboxMenuItem blueLineItem = new CheckboxMenuItem("Blue Line");
CheckboxMenuItem purpleLineItem = new CheckboxMenuItem("Purple Line");
CheckboxMenuItem grayLineItem = new CheckboxMenuItem("Gray Line");
CheckboxMenuItem blackFillItem = new CheckboxMenuItem("Black Fill", true);
CheckboxMenuItem redFillItem = new CheckboxMenuItem("Red Fill");
CheckboxMenuItem orangeFillItem = new CheckboxMenuItem("Orange Fill");
CheckboxMenuItem yellowFillItem = new CheckboxMenuItem("Yellow Fill");
CheckboxMenuItem greenFillItem = new CheckboxMenuItem("Green Fill");
CheckboxMenuItem blueFillItem = new CheckboxMenuItem("Blue Fill");
CheckboxMenuItem purpleFillItem = new CheckboxMenuItem("Purple Fill");
CheckboxMenuItem grayFillItem = new CheckboxMenuItem("Gray Fill");
Menu sizeMenu = new Menu("Size");
CheckboxMenuItem oneItem = new CheckboxMenuItem("One", true);
CheckboxMenuItem twoItem = new CheckboxMenuItem("Two");
CheckboxMenuItem threeItem = new CheckboxMenuItem("Three");
CheckboxMenuItem fourItem = new CheckboxMenuItem("Four");
CheckboxMenuItem fiveItem = new CheckboxMenuItem("Five");
protected E3G04()
{
// Add everything to the menu bar and then
// add the menu bar to the frame
mb.add(fileMenu);
mb.add(drawMenu);
fileMenu.add(newItem);
fileMenu.add(quitItem);
drawMenu.add(typeMenu);
drawMenu.add(fillMenu);
drawMenu.add(colorMenu);
drawMenu.add(sizeMenu);
typeMenu.add(ovalItem);
typeMenu.add(rectItem);
typeMenu.add(lineItem);
fillMenu.add(fillItem);
fillMenu.add(noFillItem);
if (fill && type != "line")
{
enableAllColors();
}
else
{
disableFillColor();
}
sizeMenu.add(oneItem);
sizeMenu.add(twoItem);
sizeMenu.add(threeItem);
sizeMenu.add(fourItem);
sizeMenu.add(fiveItem);
setMenuBar(mb);
//Set all of the listeners
newItem.addActionListener(this);
quitItem.addActionListener(this);
ovalItem.addItemListener(this);
rectItem.addItemListener(this);
lineItem.addItemListener(this);
fillItem.addItemListener(this);
noFillItem.addItemListener(this);
blackLineItem.addItemListener(this);
redLineItem.addItemListener(this);
orangeLineItem.addItemListener(this);
yellowLineItem.addItemListener(this);
greenLineItem.addItemListener(this);
blueLineItem.addItemListener(this);
purpleLineItem.addItemListener(this);
grayLineItem.addItemListener(this);
oneItem.addItemListener(this);
twoItem.addItemListener(this);
threeItem.addItemListener(this);
fourItem.addItemListener(this);
fiveItem.addItemListener(this);
drawingpanel = new Panel();
drawingpanel.setLayout(null);
drawingpanel.setSize(800,600);
drawingpanel.addMouseListener(this);
drawingpanel.addMouseMotionListener(this);
setBounds(100,100,800,600);
setLayout(new BorderLayout());
add("Center",drawingpanel);
addWindowListener(this);
setResizable(true);
pack();
setVisible(true);
thread.start();
}
public static void main(String [] args)
{
new E3G04();
}
public void run()
{
obj = getGraphics();
System.out.print("here");
obj.setColor(Color.black);
obj.drawRect(200,200,100,100);
obj.fillRect(200,200,100,100);
while(running)
{
//other stuff to come
}
}
public void stop()
{
drawingpanel.removeMouseListener(this);
newItem.removeActionListener(this);
quitItem.removeActionListener(this);
ovalItem.removeItemListener(this);
rectItem.removeItemListener(this);
lineItem.removeItemListener(this);
fillItem.removeItemListener(this);
noFillItem.removeItemListener(this);
blackLineItem.removeItemListener(this);
redLineItem.removeItemListener(this);
orangeLineItem.removeItemListener(this);
yellowLineItem.removeItemListener(this);
greenLineItem.removeItemListener(this);
blueLineItem.removeItemListener(this);
purpleLineItem.removeItemListener(this);
grayLineItem.removeItemListener(this);
oneItem.removeItemListener(this);
twoItem.removeItemListener(this);
threeItem.removeItemListener(this);
fourItem.removeItemListener(this);
fiveItem.removeItemListener(this);
dispose();
System.exit(0);
}
public void disableFillColor()
{
colorMenu.removeAll();
colorMenu.add(blackLineItem);
colorMenu.add(redLineItem);
colorMenu.add(orangeLineItem);
colorMenu.add(yellowLineItem);
colorMenu.add(greenLineItem);
colorMenu.add(blueLineItem);
colorMenu.add(purpleLineItem);
colorMenu.add(grayLineItem);
}
public void enableAllColors()
{
colorMenu.removeAll();
colorMenu.add(blackLineItem);
colorMenu.add(redLineItem);
colorMenu.add(orangeLineItem);
colorMenu.add(yellowLineItem);
colorMenu.add(greenLineItem);
colorMenu.add(blueLineItem);
colorMenu.add(purpleLineItem);
colorMenu.add(grayLineItem);
colorMenu.addSeparator();
colorMenu.add(blackFillItem);
colorMenu.add(redFillItem);
colorMenu.add(orangeFillItem);
colorMenu.add(yellowFillItem);
colorMenu.add(greenFillItem);
colorMenu.add(blueFillItem);
colorMenu.add(purpleFillItem);
colorMenu.add(grayFillItem);
}
public void actionPerformed(ActionEvent e)
{
Object o = e.getSource();
if (o == newItem)
{
//Clear Screen
}
if (o == quitItem)
{
thread.stop();
running = false;
stop();
}
}
public void mouseClicked(MouseEvent m)
{
Object o = m.getSource();
}
public void mousePressed(MouseEvent m)
{
start = m.getPoint();
end = start;
cur = start;
}
public void mouseDragged(MouseEvent m)
{
cur = m.getPoint();
}
public void mouseReleased(MouseEvent m)
{
end = cur;
}
public void itemStateChanged(ItemEvent e)
{
//Code removed for brevity
}
public void windowClosing(WindowEvent e)
{
running = false;
stop();
}
public void mouseExited(MouseEvent m)
{}
public void mouseEntered(MouseEvent m)
{}
public void mouseMoved(MouseEvent m)
{ }
public void windowClosed(WindowEvent e){}
public void windowOpened(WindowEvent e){}
public void windowActivated(WindowEvent e){}
public void windowDeactivated(WindowEvent e){}
public void windowIconified(WindowEvent e){}
public void windowDeiconified(WindowEvent e){}
}
爲什麼使用'Thread'？爲什麼要維護對'Graphics'上下文的引用？你爲什麼使用AWT？ – MadProgrammer
嗯，我正在使用一個線程，以便（最終）我可以使用MouseListener在屏幕上繪製更多形狀。如果我不使用線程，運行中的循環會不會阻止我與框架交互？至於保持對Graphics上下文的引用，我不確定我是否明白你的意思。而使用AWT，這僅僅是因爲我寫這個作爲期末考試的練習（其中包括AWT），所以揮杆不會有幫助。 –
AWT在它自己的'Thread'中運行，即所謂的Event Dispatching Thread。像Swing一樣，AWT是一個事件驅動的環境，你不需要像許多其他語言那樣的「主循環」。只需運行程序並回應事件 – MadProgrammer