1 //利用FontMetrics类居中 2 import javax.swing.*; 3 import java.awt.*; 4 public class TestCenterMessage extends JFrame{ 5    public TestCenterMessage(){ 6        CenterMessage messagePanel = new CenterMessage(); 7        add(messagePanel); 8        messagePanel.setBackground(Color.WHITE); 9        messagePanel.setFont(new Font("Californian FB",Font.BOLD,30));10     }11     public static void main(String[] agrs){12         JFrame frame = new TestCenterMessage();13         frame.setBounds(200,300,300,150);14         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);15         frame.setVisible(true);16     }17 }18 19 class CenterMessage extends JPanel{20    protected void paintComponent(Graphics g){21        super.paintComponent(g);22        23        //得到当前的font metrics24        FontMetrics fm = g.getFontMetrics();25        26        int stringWidth = fm.stringWidth("Welcome to Java");27        int stringAscent = fm.getAscent();28        29        int xCoordinate = getWidth()/2 - stringWidth/2;30        int yCoordinate = getHeight()/2 +stringAscent/2;31        32        g.drawString("Welcome to Java",xCoordinate,yCoordinate);33     }34 }

 

 对比：

仔细观察，字符串稍微偏高

1 import javax.swing.*; 2 import java.awt.*; 3 public class TestCenterMessage extends JFrame{ 4    public TestCenterMessage(){ 5        CenterMessage messagePanel = new CenterMessage(); 6        add(messagePanel); 7        messagePanel.setBackground(Color.WHITE); 8        messagePanel.setFont(new Font("Californian FB",Font.BOLD,30)); 9     }10     public static void main(String[] agrs){11         JFrame frame = new TestCenterMessage();12         frame.setBounds(200,300,300,150);13         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);14         frame.setVisible(true);15     }16 }17 18 class CenterMessage extends JPanel{19    protected void paintComponent(Graphics g){20        super.paintComponent(g);21        22        //得到当前的font metrics23        FontMetrics fm = g.getFontMetrics();24        25        int stringWidth = fm.stringWidth("Welcome to Java");26        int stringAscent = fm.getAscent();27        28        int xCoordinate = getWidth()/2 - stringWidth/2;29        //int yCoordinate = getHeight()/2 +stringAscent/2;30        int yCoordinate = getHeight()/2;31 32        g.drawString("Welcome to Java",xCoordinate,yCoordinate);33     }34 }