[英]Java: Graphics Disappear upon clicking JButton
For my algorithms class we have to sort an array using mergesort and at each step draw the array as a histogram to graphically see what is going on. 对于我的算法类,我们必须使用mergesort对数组进行排序,并在每一步将数组绘制为直方图,以图形方式查看正在发生的事情。 I am running into a problem with the paintComponent method updating the array.
我遇到了paintComponent方法更新数组的问题。 When I run the program for the first time, it shows the jumbled array (as it should) and then when I click the mergesort button, I am expecting to see the sorted array but instead, I get nothing.
当我第一次运行程序时,它会显示混乱的数组(应该如此)然后当我单击mergesort按钮时,我希望看到排序的数组,但相反,我什么也得不到。 Any help would be appreciated, thanks.
任何帮助将不胜感激,谢谢。
Note: I know I'm not using mergesort now, I am just trying to get the graphics working first. 注意:我知道我现在不使用mergesort,我只是想让图形先运行。
package a2;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Arrays;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
public class GraphicalSort extends JFrame implements ActionListener {
static int[] data = new int[200];
JPanel panel = new JPanel(); //Panel to hold graphical display of array
JPanel buttonsPanel = new JPanel();
JButton mButton = new JButton("Mergesort");
int xPos = 0;
static int barWidth = 8;
static int barHeight = 1;
public GraphicalSort() {
setLayout(new BorderLayout());
mButton.addActionListener(this);
buttonsPanel.add(mButton);
for (int i = 0; i < data.length; i++) {
data[i] = (int) (500 * Math.random() + 1);
}
setSize(barWidth * data.length, barHeight * 500 + buttonsPanel.getHeight());
panel = new ArrayPanel();
add(buttonsPanel, BorderLayout.NORTH);
add(panel, BorderLayout.CENTER);
repaint();
validate();
}
public static void main(String[] args) {
GraphicalSort gs = new GraphicalSort();
gs.setTitle("Graphical Sort");
gs.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
gs.setLocationRelativeTo(null);
gs.setResizable(false);
gs.setVisible(true);
}
@SuppressWarnings("serial")
class ArrayPanel extends JPanel {
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.BLACK);
for (int i = 0; i < data.length; i++) {
g.fillRect(xPos, (barHeight * 500) - (barHeight * data[i]), barWidth, barHeight * data[i]);
xPos += barWidth;
}
}
}
@Override
public void actionPerformed(ActionEvent e) {
remove(panel);
if (e.getSource() == mButton) {
Arrays.sort(data);
panel = new ArrayPanel();
}
add(panel, BorderLayout.CENTER);
repaint();
validate();
}
}
You need to reset your xPos
variable, otherwise the x co-ordinate will appear off-screen: 您需要重置
xPos
变量,否则x坐标将出现在屏幕外:
int xPos = 0;
Aside: creating a new ArrayPanel
is unnecessary — just resetting the variables and calling repaint will work by making xPos
a class member variable of ArrayPanel
. 另外:创建一个新的
ArrayPanel
是不必要的 - 只需重置变量并调用repaint就可以使xPos
成为ArrayPanel
的类成员变量。
You aren't reseting the xPos instance variable which really should not be an instance variable because you only need it in the paintComponent. 您没有重置xPos实例变量,它实际上不应该是实例变量,因为您只需要在paintComponent中使用它。 So get rid of it and move it to the paintComponent() method.
所以摆脱它并将其移动到paintComponent()方法。
You also don't need to remove and re-add the panel. 您也不需要删除并重新添加面板。 So here is what I did (note the removal of the statics! Those should be instance variables):
所以这就是我做的(注意删除静态!那些应该是实例变量):
int[] data = new int[200];
JPanel panel;
JPanel buttonsPanel = new JPanel();
JButton mButton = new JButton("Mergesort");
int barWidth = 8;
int barHeight = 1;
class ArrayPanel extends JPanel {
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.BLACK);
int xPos = 0;
for (int i = 0; i < data.length; i++) {
System.out.println("Drawing " + i);
g.fillRect(xPos, (barHeight * 500) - (barHeight * data[i]), barWidth, barHeight * data[i]);
xPos += barWidth;
}
}
}
public void actionPerformed(ActionEvent e) {
Arrays.sort(data);
panel.repaint();
}
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