如何在JFrame中删除绘制的字符串

Question

So basically I want to have a number system on a JFrame panel. The number is displayed on the frame using this method.

public static void text(int x, int y, String text)
{
if (instance == null)
  throw new RuntimeException("Must call window method first");
Graphics g = image.getGraphics();
g.setColor(color);
Font font = new Font(null, Font.PLAIN, fontSize);
g.setFont(font);
FontMetrics metrics = g.getFontMetrics();
int actualX = x - metrics.stringWidth(text) / 2;
int actualY = y + metrics.getAscent() / 2;
g.drawString(text, actualX, actualY);

instance.repaint();
}

When the value of the number increases I want it to replace the number up there with the new number. I know there has to be a way to do this but could someone help me with finding it? Thanks so much.

Answer 1

you need to clear the drawn are, then draw the string again.

public static void image(int x, int y, int width, int height, String file)
{
if (instance == null)
  throw new RuntimeException("Must call window method first");
Graphics g = image.getGraphics();
////
g.setColor(bgColor);//background color
g.fillRect(0,0,image.getWidth(),image.getHeigth());//clearing the are by filling a rectangle
////
g.setColor(color);
Font font = new Font(null, Font.PLAIN, fontSize);
g.setFont(font);
FontMetrics metrics = g.getFontMetrics();
int actualX = x - metrics.stringWidth(text) / 2;
int actualY = y + metrics.getAscent() / 2;
g.drawString(text, actualX, actualY);

instance.repaint();
}

Answer 2

You should NOT use the getGraphics() method to do painting. For future reference read the Swing tutorial on Custom Painting for the proper way to do something like this.

However, you should not even be using custom painting for this requirement. Instead you should just be using a JLabel . Then when you want to change the string you just invoke the setText() method of the label.