//全局字体设置-----------------------// 
Font font1 = new Font("宋体",Font.PLAIN,12); 
Font font2 = new Font("宋体",Font.PLAIN,15);   
UIManager.put("Button.font",font1);    
UIManager.put("OptionPane.messageFont",font2);   
UIManager.put("OptionPane.buttonFont",font1);或者试试
UIManager.setLookAndFeel("com.sun.java.swing.plaf.motif.MotifLookAndFeel");
SwingUtilities.updateComponentTreeUI(JFrame);UIManager.setLookAndFeel("com.sun.java.swing.plaf.metal.MetalLookAndFeel" );
SwingUtilities.updateComponentTreeUI(JFrame);