Java GUI: Add JPanel into JScrollPane

Goals to achieve:

Because there are a number of Java GUI components in the scroll box, the JPanel panel is used to wrap these components in a scroll-through-jscrollpane implementation.

Question 1: The layout rubs together

JPanel has its own default layout, so here we have to set the flow layout ourselves

Jpanel_qanda.setlayout (null);

Issue 2: Scroll bar does not take effect

At first I was setting the size of the JPanel directly. setSize (int width, int height) No matter how large the setting is, there is no scroll bar

Finally Baidu, saw a blog: https://www.cnblogs.com/tianguook/archive/2012/03/21/2410807.html

Jpanel_qanda.setpreferredsize (new Dimension (800,1000));

Scroll bar appears!

Issue 3: Component does not display

PS: Today, when writing the GUI, because of carelessness, there is a problem:

Container add component, the runtime does not appear, when the mouse moved to the target location, the component only surfaced

Cause: SetBounds is written in front of the Add method.

Paste all the code, for personal use, a bit messy:

 Public Static voidQandA () {FinalJFrame Frame=menu (NewJFrame ()); User.setnickname ("Zs"); User.setrole (1); List<Qanda> questions=qandadao.getquestions (); JButton Jbutton_ask=NewJButton ("Ask Question");        Frame.add (Jbutton_ask); Jbutton_ask.setbounds (440, 200, 120, 30); Jbutton_ask.addactionlistener (NewActionListener () {@Override Public voidactionperformed (ActionEvent e) {//TODO auto-generated Method Stub                            }        }); JPanel Jpanel_qanda=NewJPanel (); Jpanel_qanda.setpreferredsize (NewDimension (800,150*questions.size ())); Jpanel_qanda.setlayout (NULL);  for(inti = 0; I < questions.size (); i++) {String name=Questions.get (i). GetName (); String Time=Questions.get (i). GetTime (); String content=Questions.get (i). GetContent (); JLabel Jlabel_name=NewJLabel ("Name:" +name);            Jpanel_qanda.add (Jlabel_name); Jlabel_name.setbounds (20+150*i, 60, 20); JLabel Jlabel_time=NewJLabel ("Time:" +Time );            Jpanel_qanda.add (Jlabel_time); Jlabel_time.setbounds (20+150*i, 160, 20); JButton Jbutton_answer=NewJButton ("Answer");            Jpanel_qanda.add (Jbutton_answer); Jbutton_answer.setbounds (420, 20+150*i, 120, 30); Jbutton_answer.addactionlistener (NewActionListener () {@Override Public voidactionperformed (ActionEvent e) {//TODO auto-generated Method Stub                                    }            }); JButton Jbutton_check=NewJButton ("Check");            Jpanel_qanda.add (Jbutton_check); Jbutton_check.setbounds (620, 20+150*i, 120, 30); Jbutton_check.addactionlistener (NewActionListener () {@Override Public voidactionperformed (ActionEvent e) {//TODO auto-generated Method Stub                                    }            }); JTextArea jtextarea_content=NewJTextArea (content);            Jpanel_qanda.add (jtextarea_content); Jtextarea_content.setbounds (50+150*i, 740, 80); } JScrollPane jscrollpane_userinfo=NewJScrollPane (Jpanel_qanda,scrollpaneconstants.vertical_scrollbar_always, Scrollpaneconstants.horizontal        _scrollbar_always);        Frame.add (Jscrollpane_userinfo); Jscrollpane_userinfo.setbounds (100, 250, 800, 200); Jscrollpane_userinfo.setfont (NewFont ("Dialog", 0, 20)); }    /*** User Information*/     Public Static voidUserInfo () {JFrame frame=NewJFrame (); User.setnickname ("Zs"); Frame.setsize (1000,600); Frame.setvisible (true); Frame.setresizable (false); Frame.setlocation ((Toolkit.getdefaulttoolkit (). Getscreensize (). Width-400)/2, (Toolkit.getdefaulttoolkit (). Getscreensize (). Height-320)/2); Frame.settitle ("Notice"); Frame.setlayout (NULL); Frame=menu (frame); List<User> users=userdao.getusers (); String[][] Userinfos=NewString[users.size ()][4];  for(intI=0;i<users.size (); i++) {userinfos[i][0]=Users.get (i). Getnickname (); userinfos[i][1]=Users.get (i). Getaccount (); userinfos[i][2]=Users.get (i). Getemail (); if(Users.get (i). Getrole () ==0) {userinfos[i][3]= "Student"; }Else{userinfos[i][3]= "Teacher"; }} string[] Header=Newstring[]{"Name", "Account", "Email", "Role"}; JTable Jtable_userinfo=NewJTable (Userinfos,header); JScrollPane Jscrollpane_userinfo=NewJScrollPane (Jtable_userinfo,scrollpaneconstants.vertical_scrollbar_always, Scrollpaneconstants.horizon        Tal_scrollbar_always);        Frame.add (Jscrollpane_userinfo); Jscrollpane_userinfo.setbounds (100, 200, 800, 200); Jscrollpane_userinfo.setfont (NewFont ("Dialog", 0, 20)); }

Java GUI: Add JPanel into JScrollPane