setUndecorated無法使用非默認外觀

Question

import javax.swing.JDialog; 
import javax.swing.JFrame; 
import javax.swing.UIManager; 
import javax.swing.UnsupportedLookAndFeelException; 

public class Frame { 

    private JFrame jFrame; 

    public Frame() { 
     try { 
      UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName()); 
      JFrame.setDefaultLookAndFeelDecorated(true); 
      JDialog.setDefaultLookAndFeelDecorated(true); 
     } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException e) { 
      e.printStackTrace(); 
     } 
    } 

    private void create() { 
     jFrame = new JFrame("frame"); 
     jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     jFrame.setSize(200, 200); 
     jFrame.setVisible(true); 
    } 

    public static void main(String[] args) { 
     new Frame().create(); 
    } 

} 

上面的代碼工作正常，但如果我將jFrame.undecorated設置爲true，它不會刪除框架？有誰知道爲什麼不呢？謝謝。

編輯：另外發現，如果我將jFrame.undecorated設置爲false，另一個具有默認外觀和感覺的框架也會顯示。就像這樣：

Answer 1

檢查的setUndecorated（）方法的文檔 - 只能在不可見的調用。帶有兩個調用的代碼在構造函數中註釋掉，但添加了jFrame.setUndecorated（true）;在setVisible（）調用之前。

import javax.swing.JDialog; 
import javax.swing.JFrame; 
import javax.swing.UIManager; 
import javax.swing.UnsupportedLookAndFeelException; 

public class Frame { 

private JFrame jFrame; 

public Frame() { 
    try { 
       UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName()); 
     //JFrame.setDefaultLookAndFeelDecorated(true); 
     //JDialog.setDefaultLookAndFeelDecorated(true); 

    } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException e) { 
     e.printStackTrace(); 
    } 
} 

private void create() { 
    jFrame = new JFrame("frame"); 
    jFrame.setUndecorated(true); 
    jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    jFrame.setSize(200, 200); 
    jFrame.setVisible(true); 

} 

public static void main(String[] args) { 
    new Frame().create(); 
} 

}