setBackground语句不工作？

Question

import javax.swing.JApplet;
import java.awt.*;

public class Snowman extends JApplet {
//---------------------------------------------
// Draws a snowman.
//---------------------------------------------
public void paint (Graphics page)
{
    final int MID = 150;
    final int TOP = 50;

    setBackground (Color.cyan);

    page.setColor(Color.blue);
    page.fillRect(0, 175, 300, 50); // ground

    page.setColor (Color.yellow);
    page.fillOval (-40, -40, 80, 80); // sun

    page.setColor (Color.white);
    page.fillOval (MID-20, TOP, 40, 40); // head
    page.fillOval (MID-35, TOP+35, 70, 50); // upper torso
    page.fillOval (MID-50, TOP+80, 100, 60); // lower torso

    page.setColor (Color.black);
    page.fillOval(MID-10, TOP+10, 5, 5);
    page.fillOval(MID+5, TOP+10, 5, 5);

    page.drawArc(MID-10, TOP+20, 20, 10, 190, 160); // smile

    page.drawLine (MID-25, TOP+60, MID-50, TOP+40); // left arm
    page.drawLine (MID+25, TOP+60, MID+55, TOP+60); // right arm

    page.drawLine (MID-20, TOP+5, MID+20, TOP+5); // brim of hat
    page.fillRect(MID-15, TOP-20, 30, 25); // top of hat
}
}

这就是所有的代码。setBackground是在我声明了两个最终变量之后声明的，提前谢谢，我从一本书"Java Software Solutions“中得到了这段代码，我一遍又一遍地看了一遍，没有运气:/提前谢谢:)

Answer 1

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//<applet code='Snowman' width=300 height=200></applet>
import javax.swing.*;
import java.awt.*;

public class Snowman extends JApplet {
//---------------------------------------------
// Draws a snowman.
//---------------------------------------------
    public void init() {
        add(new SnowmanPanel());
        validate();
    }
}

class SnowmanPanel extends JPanel {

    final int MID = 150;
    final int TOP = 50;

    SnowmanPanel() {
        setBackground (Color.cyan);
    }

    public void paintComponent(Graphics page)
    {
        super.paintComponent(page);

        page.setColor(Color.blue);
        page.fillRect(0, 175, 300, 50); // ground

        page.setColor (Color.yellow);
        page.fillOval (-40, -40, 80, 80); // sun

        page.setColor (Color.white);
        page.fillOval (MID-20, TOP, 40, 40); // head
        page.fillOval (MID-35, TOP+35, 70, 50); // upper torso
        page.fillOval (MID-50, TOP+80, 100, 60); // lower torso

        page.setColor (Color.black);
        page.fillOval(MID-10, TOP+10, 5, 5);
        page.fillOval(MID+5, TOP+10, 5, 5);

        page.drawArc(MID-10, TOP+20, 20, 10, 190, 160); // smile

        page.drawLine (MID-25, TOP+60, MID-50, TOP+40); // left arm
        page.drawLine (MID+25, TOP+60, MID+55, TOP+60); // right arm

        page.drawLine (MID-20, TOP+5, MID+20, TOP+5); // brim of hat
        page.fillRect(MID-15, TOP-20, 30, 25); // top of hat
    }
}

一般的建议。

• 不要在顶级Swing组件中进行绘制。相反，将自定义绘画移动到JPanel或JComponent中，并在那里进行绘画。对于后者中的自定义绘制，覆盖paintComponent(Graphics)
• When执行自定义绘制，请记住在构造函数(或init())中调用super.paintComponent(Graphics)
• Set而不是在paint方法中调用颜色。

其他建议

• 对于静态图像，您还可以将其绘制为BufferedImage，然后将图像放入JLabel的ImageIcon中。这更简单。
• 如果这本书急于创建applet，那就把它扔掉。小应用程序比标准应用程序要难得多，新手不应该尝试。

Answer 2

试试这段代码

import java.awt.*;
import javax.swing.JApplet;

public class SnowMan extends JApplet
{

    public SnowMan()
    {
        setBackground(Color.cyan);
    }
//---------------------------------------------
// Draws a snowman.
//---------------------------------------------


    @Override
    public void paint(Graphics page)
    {
        final int MID = 150;
        final int TOP = 50;



        page.setColor(Color.blue);
        page.fillRect(0, 175, 300, 50); // ground

        page.setColor(Color.yellow);
        page.fillOval(-40, -40, 80, 80); // sun

        page.setColor(Color.white);
        page.fillOval(MID - 20, TOP, 40, 40); // head
        page.fillOval(MID - 35, TOP + 35, 70, 50); // upper torso
        page.fillOval(MID - 50, TOP + 80, 100, 60); // lower torso

        page.setColor(Color.black);
        page.fillOval(MID - 10, TOP + 10, 5, 5);
        page.fillOval(MID + 5, TOP + 10, 5, 5);

        page.drawArc(MID - 10, TOP + 20, 20, 10, 190, 160); // smile

        page.drawLine(MID - 25, TOP + 60, MID - 50, TOP + 40); // left arm
        page.drawLine(MID + 25, TOP + 60, MID + 55, TOP + 60); // right arm

        page.drawLine(MID - 20, TOP + 5, MID + 20, TOP + 5); // brim of hat
        page.fillRect(MID - 15, TOP - 20, 30, 25); // top of hat
    }
}

Answer 3

setBackground (Color.cyan);

它在我的IDE中工作正常。我还正确地更改了background.It works的颜色。在创建类时，不需要更改code.Make。