import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.JLabel;
import javax.swing.JScrollPane;
import javax.swing.JPanel;

import java.awt.Dimension;
import java.awt.Component;
import java.awt.GridLayout;
class Test{
    JFrame jframe;
    JLabel jlabel1;
    JLabel jlabel2;
    JLabel jlabel3;
    JLabel jlabel4;
    JScrollPane jscrollpane;
    JPanel jpanel;
    
    Dimension size;

    Test(){
        jframe=new JFrame();
        jpanel=new JPanel(new GridLayout(4,1));
        jlabel1=new JLabel("label1");
        jlabel2=new JLabel("label2");
        jlabel3=new JLabel("label3");
        jlabel4=new JLabel("label4");
        jpanel.add(jlabel1);
        jpanel.add(jlabel2);
        jpanel.add(jlabel3);
        jpanel.add(jlabel4);
        jpanel.setPreferredSize(new Dimension(200,200));

        jscrollpane=new JScrollPane(jpanel);
        jscrollpane.setSize(100,100);
        
        jframe.add(jscrollpane);
        jframe.setSize(new Dimension(300,300));
        jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jframe.setVisible(true);
        jframe.setLayout(null);
        }
    public static void main(String arr[]){
        SwingUtilities.invokeLater(new Runnable(){public void run(){new Test();}});
        }
    }
    

JPanel的size比jscrollpane还要大，为什么没出现滚动条？