为什么在更改JScrollPane上的大小时更改JPanel中的对象（JPanel）？

Question

每当我改变这行代码时：

scrollPane.setSize(new Dimension(500, 500));

到

scrollPane.setSize(new Dimension(500, 600));

我的JPanel中的对象（JPanel）发生了变化吗？

查看结构的方法是：

Objects: JScrollPanel(  JPanel          (    JPanel( )    )     );
names:   scrollPanel (  tableCollection (    table1( )    )     )

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Insets;
import java.awt.Toolkit;
import javax.swing.JPanel;
import javax.swing.JScrollPane;


public class testing extends javax.swing.JFrame {

    public testing () {
        initComponents();

        setMainFrameSize();
        addScrollPane();
        addTables();
    }

    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        addComponentListener(new java.awt.event.ComponentAdapter() {
            public void componentResized(java.awt.event.ComponentEvent evt) {
                formComponentResized(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 400, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 300, Short.MAX_VALUE)
        );

        pack();
    }// </editor-fold>                        

    private void formComponentResized(java.awt.event.ComponentEvent evt) {                                      
        setScrollPaneSize();
        setTableSize();
    }                                     

    public static void main(String args[]) {
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(testing.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(testing.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(testing.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(testing.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new testing().setVisible(true);
            }
        });
    }

    JPanel tableCollection = new JPanel();
    JScrollPane scrollPane = new JScrollPane(tableCollection, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                                             JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);

    // Variables declaration - do not modify                     
    // End of variables declaration                   

    void setMainFrameSize() {
        this.setMinimumSize(new Dimension(800, 600));
        Dimension scnDimension = Toolkit.getDefaultToolkit().getScreenSize();
        Insets scnInsets = Toolkit.getDefaultToolkit().getScreenInsets(getGraphicsConfiguration());
        this.setSize(scnDimension.width, scnDimension.height-(scnInsets.bottom+scnInsets.top));
    }

    void addScrollPane() {
        scrollPane.setBackground(Color.red);
        setScrollPaneSize();
        this.add(scrollPane);

        addTableCollection();
    }
    void setScrollPaneSize() {
        scrollPane.setSize(new Dimension(500, 500));
        scrollPane.setLocation(0, barHeight);
    }

    void addTableCollection() {
        tableCollection.setBackground(new Color(189, 195, 199));
        setTableCollectionSize();
    }
    void setTableCollectionSize() {
        tableCollection.setPreferredSize(new Dimension(550, 550));
    }

    void addTables() {
        table1.setBackground(new Color(52, 152, 219));

        tableCollection.add(table1);

    }
    void setTableSize() {

        int tableHeight = tableCollection.getHeight()-tableHeightOffset*2;
        table1.setSize(350, tableHeight);
        table1.setLocation(0, 0);
    }

    int barHeight = 50;
    int tableHeightOffset = 50;
    int tableWidthOffset = 50;
    int nTables = 5;

    JPanel table1 = new JPanel();

}

Answer 1

只需添加tableCollection.setLayout(null);即可在JPanel中处理自定义大小的JPanel

感谢Jonas JPanel inside another