JAVA:图形之利用FontMetrics类居中

//利用FontMetrics类居中
import javax.swing.*;
import java.awt.*;
public class TestCenterMessage extends JFrame{
   public TestCenterMessage(){
       CenterMessage messagePanel = new CenterMessage();
       add(messagePanel);
       messagePanel.setBackground(Color.WHITE);
       messagePanel.setFont(new Font("Californian FB",Font.BOLD,30));
    }
    public static void main(String[] agrs){
        JFrame frame = new TestCenterMessage();
        frame.setBounds(200,300,300,150);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

class CenterMessage extends JPanel{
   protected void paintComponent(Graphics g){
       super.paintComponent(g);
       
       //得到当前的font metrics
       FontMetrics fm = g.getFontMetrics();
       
       int stringWidth = fm.stringWidth("Welcome to Java");
       int stringAscent = fm.getAscent();
       
       int xCoordinate = getWidth()/2 - stringWidth/2;
       int yCoordinate = getHeight()/2 +stringAscent/2;
       
       g.drawString("Welcome to Java",xCoordinate,yCoordinate);
    }
}

 对比：

仔细观察，字符串稍微偏高

import javax.swing.*;
import java.awt.*;
public class TestCenterMessage extends JFrame{
   public TestCenterMessage(){
       CenterMessage messagePanel = new CenterMessage();
       add(messagePanel);
       messagePanel.setBackground(Color.WHITE);
       messagePanel.setFont(new Font("Californian FB",Font.BOLD,30));
    }
    public static void main(String[] agrs){
        JFrame frame = new TestCenterMessage();
        frame.setBounds(200,300,300,150);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

class CenterMessage extends JPanel{
   protected void paintComponent(Graphics g){
       super.paintComponent(g);
       
       //得到当前的font metrics
       FontMetrics fm = g.getFontMetrics();
       
       int stringWidth = fm.stringWidth("Welcome to Java");
       int stringAscent = fm.getAscent();
       
       int xCoordinate = getWidth()/2 - stringWidth/2;
       //int yCoordinate = getHeight()/2 +stringAscent/2;
       int yCoordinate = getHeight()/2;

       g.drawString("Welcome to Java",xCoordinate,yCoordinate);
    }
}