第8章 标签与按钮（一）

第8章 标签与按钮

　　Swing的标签和按钮分别用JLabel和JButton类表示，它们是能够显示文本或图标的简单组件。缺省时，标签没有边框，可以显示一个字符串，一个图标或同时显示字符串和图标。除了用于修饰文本域等不重要的小事情外，Swing的标签还能起到图像画布(显示一个图像的组件)的作用。由于AWT的图像不是组件，不能把它们添加到一个容器中。因此，使用AWT的开发人员实现了各种不同的图像画布类；然而，在Swing中，可以把JLabel类当作图像画面使用(注：有关图像画面的更多信息参见4.3.1“Swing组件中的定制绘制”一节)。
　　按钮大概是使用最为普遍的用户界面组件。按钮通常带有某种边框，且可以被鼠标或快捷键激活。Swing按钮比Swing标签要复杂得多，不仅因为能够激活它们来完成某个功能，而且很多其他Swing组件都是AbstractButton类的扩展，而AbstractButton类是Swing按钮的基类。

8.1 JLabel与JBution

 

8.2 JLabel

例8-1 运行中的JLabel

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

 

public class Test extends JApplet {

        public Test() {

               Container contentPane = getContentPane();

               JLabel imageOnly = new JLabel(new ImageIcon(this.getClass().getResource("dogs.gif")));

               JLabel textAndImage = new JLabel("Vote!",

                                              new ImageIcon(this.getClass().getResource("ballot_box.gif")),

                                              JLabel.RIGHT);

 

               JScrollPane scrollPane = new JScrollPane(imageOnly);

               scrollPane.setPreferredSize(new Dimension(270,200));

 

               contentPane.setLayout(

                       new FlowLayout(FlowLayout.CENTER, 25, 25));

 

               contentPane.add(textAndImage);

               contentPane.add(scrollPane);

        }

}

 

8.2.1 内容排列

 

例8-2 设置Swing标签的排列属性

import java.net.URL;

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

import javax.swing.border.*;

 

public class Test extends JApplet implements SwingConstants {

        JLabel        label   = new JLabel("Action!");

        JPanel         controlPanel   = new JPanel();

        JComboBox     alignmentHorizontal    = new JComboBox();

        JComboBox              alignmentVertical      = new JComboBox();

 

        public void init() {

               Container contentPane = getContentPane();

               ImageIcon icon = new ImageIcon(this.getClass().getResource("slate.gif"));

 

               label.setIcon(icon);

               label.setHorizontalAlignment(CENTER);

               label.setFont(new Font("Times-Roman", Font.ITALIC, 20));

 

               label.setMaximumSize(new Dimension(0, 150));

 

               setupComboBoxes();

               setupControlPanel();

 

               contentPane.setLayout(new BorderLayout());

               contentPane.add(controlPanel, "North");

               contentPane.add(label, "Center");

 

               alignmentVertical.addItemListener(new ItemListener() {

                       public void itemStateChanged(ItemEvent event) {

                               JComboBox b = (JComboBox)event.getSource();

                               String    s = (String)b.getSelectedItem();

                               int       c = getSwingConstantByName(s);

 

                               label.setVerticalAlignment(c);

                       }

               });

               alignmentHorizontal.addItemListener(new ItemListener() {

                       public void itemStateChanged(ItemEvent event) {

                               JComboBox b = (JComboBox)event.getSource();

                               String    s = (String)b.getSelectedItem();

                               int       c = getSwingConstantByName(s);

                             

                               label.setHorizontalAlignment(c);

                       }

               });

        }

        void setupComboBoxes() {

               alignmentVertical.addItem("Top");

               alignmentVertical.addItem("Center");

               alignmentVertical.addItem("Bottom");

 

               alignmentHorizontal.addItem("Left");

               alignmentHorizontal.addItem("Center");

               alignmentHorizontal.addItem("Right");

 

               alignmentVertical.setSelectedItem(

                       getSwingConstantName(

                               label.getVerticalAlignment()));

 

               alignmentHorizontal.setSelectedItem(

                       getSwingConstantName(

                               label.getHorizontalAlignment()));

        }

        void setupControlPanel() {

               controlPanel.setBorder(

                       BorderFactory.createTitledBorder("Alignment"));

 

               controlPanel.add(new JLabel(

                                              "Vertical:"));

               controlPanel.add(alignmentVertical);

               controlPanel.add(Box.createHorizontalStrut(5));

 

               controlPanel.add(Box.createHorizontalStrut(25));

 

               controlPanel.add(new JLabel(

                                              "Horizontal:"));

               controlPanel.add(Box.createHorizontalStrut(5));

 

               controlPanel.add(alignmentHorizontal);

        }

        int getSwingConstantByName(String s) {

               if(s.equalsIgnoreCase("left"))                return LEFT;

               else if(s.equalsIgnoreCase("center"))         return CENTER;

               else if(s.equalsIgnoreCase("right"))          return RIGHT;

               else if(s.equalsIgnoreCase("top"))            return TOP;

               else if(s.equalsIgnoreCase("bottom"))         return BOTTOM;

 

               return -1;

        }

        String getSwingConstantName(int c) {

               if(c == LEFT)                  return "Left";

               else if(c == CENTER)   return "Center";

               else if(c == RIGHT)    return "Right";

               else if(c == TOP)              return "Top";

               else if(c == BOTTOM)   return "Bottom";

 

               return "undefined";

        }

}

8.2.2 文本的位置

 

例8-3 设置标签的文本位置

import java.net.URL;

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

import javax.swing.border.*;

 

public class Test extends JApplet implements SwingConstants {

        JLabel label = new JLabel("Action!");

        JPanel controlPanel = new JPanel();

        JComboBox alignmentHorizontal = new JComboBox();

        JComboBox alignmentVertical = new JComboBox();

 

        public void init() {

               Container contentPane = getContentPane();

               ImageIcon icon = new ImageIcon(this.getClass().getResource("penguin.gif"));

 

               label.setIcon(icon);

               label.setHorizontalTextPosition(CENTER);

               label.setFont(new Font("Times-Roman", Font.ITALIC, 20));

 

               setupComboBoxes();

               setupControlPanel();

 

               label.setHorizontalAlignment(JLabel.CENTER);

               label.setVerticalAlignment(JLabel.CENTER);

 

               contentPane.setLayout(new BorderLayout());

               contentPane.add(controlPanel, "North");

               contentPane.add(label, "Center");

 

               alignmentVertical.addItemListener(new ItemListener() {

                       public void itemStateChanged(ItemEvent event) {

                               JComboBox b = (JComboBox)event.getSource();

                               String    s = (String)b.getSelectedItem();

                               int       c = getSwingConstantByName(s);

 

                               label.setVerticalTextPosition(c);

                       }

               });

               alignmentHorizontal.addItemListener(new ItemListener() {

                       public void itemStateChanged(ItemEvent event) {

                               JComboBox b = (JComboBox)event.getSource();

                               String    s = (String)b.getSelectedItem();

                               int       c = getSwingConstantByName(s);

                              

                               label.setHorizontalTextPosition(c);

                       }

               });

        }

        void setupComboBoxes() {

               alignmentVertical.addItem("Top");

               alignmentVertical.addItem("Center");

               alignmentVertical.addItem("Bottom");

 

               alignmentHorizontal.addItem("Left");

               alignmentHorizontal.addItem("Center");

               alignmentHorizontal.addItem("Right");

 

               alignmentVertical.setSelectedItem(

                       getSwingConstantName(

                               label.getVerticalTextPosition()));

 

               alignmentHorizontal.setSelectedItem(

                       getSwingConstantName(

                               label.getHorizontalTextPosition()));

        }

        void setupControlPanel() {

               controlPanel.setBorder(

                       BorderFactory.createTitledBorder("Text Position"));

 

               controlPanel.add(new JLabel( "Vertical:"));

               controlPanel.add(alignmentVertical);

               controlPanel.add(Box.createHorizontalStrut(5));

 

               controlPanel.add(Box.createHorizontalStrut(25));

 

               controlPanel.add(new JLabel("Horizontal:"));

               controlPanel.add(Box.createHorizontalStrut(5));

 

               controlPanel.add(alignmentHorizontal);

        }

        int getSwingConstantByName(String s) {

               if(s.equalsIgnoreCase("left"))                return LEFT;

               else if(s.equalsIgnoreCase("center"))         return CENTER;

               else if(s.equalsIgnoreCase("right"))          return RIGHT;

               else if(s.equalsIgnoreCase("top"))            return TOP;

               else if(s.equalsIgnoreCase("bottom"))         return BOTTOM;

 

               return -1;

        }

        String getSwingConstantName(int c) {

               if(c == LEFT)                  return "Left";

               else if(c == CENTER)   return "Center";

               else if(c == RIGHT)    return "Right";

               else if(c == TOP)              return "Top";

               else if(c == BOTTOM)   return "Bottom";

 

               return "undefined";

        }

}

8.2.3 图标/文本间隙

 

例8-4 设置一个标签的图标/文本间隙

import java.net.URL;

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

import javax.swing.border.*;

 

public class Test extends JApplet implements SwingConstants {

        public void init() {

               Container contentPane = getContentPane();

               JComboBox iconTextGap = new JComboBox();

               JPanel controlPanel = new JPanel();

               ImageIcon icon = new ImageIcon(this.getClass().getResource("ladybug.gif"));

 

               final JLabel label = new JLabel("Lady Bug", icon, CENTER);

 

               label.setFont(new Font("Times-Roman", Font.ITALIC, 20));

 

               iconTextGap.addItem("4");

               iconTextGap.addItem("10");

               iconTextGap.addItem("15");

               iconTextGap.addItem("20");

               iconTextGap.addItem("25");

 

               controlPanel.add(new JLabel("Icon/Text Gap:"));

               controlPanel.add(iconTextGap);

 

               contentPane.setLayout(new BorderLayout());

               contentPane.add(controlPanel, "North");

               contentPane.add(label, "Center");

 

               iconTextGap.addItemListener(new ItemListener() {

                       public void itemStateChanged(ItemEvent event) {

                               JComboBox b = (JComboBox)event.getSource();

                               String    s = (String)b.getSelectedItem();

                               int       gap = Integer.parseInt(s);

                              

                               label.setIconTextGap(gap);

                       }

               });

        }

}

8.2.4 许可状态

 

例8-5 设置一个标签的许可状态

import java.net.URL;

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

import javax.swing.border.*;

 

public class Test extends JApplet implements SwingConstants {

        public void init() {

               Container contentPane = getContentPane();

               JComboBox iconTextGap = new JComboBox();

               JPanel controlPanel = new JPanel();

               ImageIcon icon = new ImageIcon(this.getClass().getResource("ladybug.gif"));

 

               final JLabel label = new JLabel("Lady Bug", icon, CENTER);

 

               label.setFont(new Font("Times-Roman", Font.ITALIC, 20));

 

               iconTextGap.addItem("4");

               iconTextGap.addItem("10");

               iconTextGap.addItem("15");

               iconTextGap.addItem("20");

               iconTextGap.addItem("25");

 

               controlPanel.add(new JLabel("Icon/Text Gap:"));

               controlPanel.add(iconTextGap);

 

               contentPane.setLayout(new BorderLayout());

               contentPane.add(controlPanel, "North");

               contentPane.add(label, "Center");

 

               iconTextGap.addItemListener(new ItemListener() {

                       public void itemStateChanged(ItemEvent event) {

                               JComboBox b = (JComboBox)event.getSource();

                               String    s = (String)b.getSelectedItem();

                               int       gap = Integer.parseInt(s);

                              

                               label.setIconTextGap(gap);

                       }

               });

        }

}

8.2.5 JLabel属性

 

8.2.6 JLabel事件