Java：GridLayout垂直元素对齐

Question

我试图垂直居中JPanel p1的第一行。其中的元素是JLabel，JTextField和另一个JPanel GridLayout，当窗口拉伸时，元素保持在其上，我该怎么办？实现我想要的目标？

import javax.swing.*;
import java.awt.*;

public class grafica extends JFrame{

private JPanel p1,p2,p3;
private JButton aggiungi, affitta, reso, cerca, stampa; 
private JTextArea a1;
private JTextField n1;
private JLabel l1;

public grafica(){
//creating panels
    p1=new JPanel();
    p2=new JPanel();
    p3=new JPanel();
    p1.setLayout(new GridLayout(2,1));
    p3.setLayout(new GridLayout(5,1));

    //creating elements
    aggiungi=new JButton("Aggiungi");
    affitta=new JButton("Affitta");
    reso=new JButton("Reso");
    cerca=new JButton("Cerca");
    stampa=new JButton("Stampa");
    n1=new JTextField(10);
    l1=new JLabel("Taglia: ");

    //adding elements
    p2.add(l1);
    p2.add(n1);
    p3.add(aggiungi);
    p3.add(affitta);
    p3.add(reso);
    p3.add(cerca);
    p3.add(stampa);
    p2.add(p3);
    p1.add(p2);

    a1=new JTextArea(20,20);
    a1.setEditable(false);
    p1.add(a1);
    p1.setBorder(BorderFactory.createMatteBorder(1, 1, 1, 1, Color.red));
    p2.setBorder(BorderFactory.createMatteBorder(1, 1, 1, 1, Color.blue));

    p3.setBorder(BorderFactory.createMatteBorder(1, 1, 1, 1, Color.green));

    this.setVisible(true);
    this.getContentPane().add(p1);
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    this.pack();
    }
}

这是我的预期结果：

Answer 1

使用其他面板按住p2并将新面板的布局设置为BoxLayout。

import javax.swing.*;
import java.awt.*;

public class grafica extends JFrame {

    private JPanel p1, p2, p3, p4;
    private JButton aggiungi, affitta, reso, cerca, stampa;
    private JTextArea a1;
    private JTextField n1;
    private JLabel l1;

    public grafica() {
        // creating panels
        p1 = new JPanel();
        p2 = new JPanel();
        p3 = new JPanel();
        p4 = new JPanel();
        p1.setLayout(new GridLayout(2, 1));
        p3.setLayout(new GridLayout(5, 1));

        // creating elements
        aggiungi = new JButton("Aggiungi");
        affitta = new JButton("Affitta");
        reso = new JButton("Reso");
        cerca = new JButton("Cerca");
        stampa = new JButton("Stampa");
        n1 = new JTextField(10);
        l1 = new JLabel("Taglia: ");

        // adding elements
        p2.add(l1);
        p2.add(n1);
        p3.add(aggiungi);
        p3.add(affitta);
        p3.add(reso);
        p3.add(cerca);
        p3.add(stampa);
        p2.add(p3);

        // added part
        JPanel p2Holder = new JPanel();
        p2Holder.setLayout(new BoxLayout(p2Holder, BoxLayout.Y_AXIS));
        p2Holder.add(Box.createVerticalGlue());
        p2Holder.add(p2);
        p2Holder.add(Box.createVerticalGlue());

        p1.add(p2Holder);

        a1 = new JTextArea(20, 20);
        a1.setEditable(false);
        p1.add(a1);
        p1.setBorder(BorderFactory.createMatteBorder(1, 1, 1, 1, Color.red));
        p2.setBorder(BorderFactory.createMatteBorder(1, 1, 1, 1, Color.blue));

        p3.setBorder(BorderFactory.createMatteBorder(1, 1, 1, 1, Color.green));

        this.setVisible(true);
        this.getContentPane().add(p1);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.pack();
    }

    public static void main(String[] args) {
        new grafica();
    }
}