How do I define the size and place of components?

Question

I created this code in java to train a little and learn but I can not set the place where the JComboBox and the JTextField will appear and the size of them as I do? I want to leave them in the middle of the window without being stuck to the edge of the window and each other and without them grabbing the whole window. setSize and setBounds are not working.

Code:

/*Biblioteca */
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;

class creator {

public static void main(String args[]){

/*Gera os campos, tela, e configurações */
JFrame frame = new JFrame();
JPanel panel = new JPanel(new BorderLayout());
JTextField texto = new JTextField();
JComboBox combo = new JComboBox();

/*Cria as opções e configurações do JComboBox */
combo.setBackground(Color.WHITE);
combo.addItem("opção1");
combo.addItem("opção2");
combo.addItem("opção3");

/*Adiciona as coisas na tela */
panel.add(texto);
panel.add(combo);

/*Configurações da janela*/
frame.setSize(500, 500);        
frame.add(panel);
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.setVisible(true); 

}

}

Answer 1

To configure size, there are methods setSize, setPreferredSize, where both define the dimensions of the component, but the second size is only relative. As most containers use layouts, they usually rely on the second method to define the size of the components, although some also rely on the methods setMaximumSize and setMinimumSize. These methods are inherited from the class JComponent and Component

The position also depends on which layout is being used, each one has a positioning feature, in the link above is presented each, you can choose which one best serves your goal, and even combine them if necessary.

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Centralizing the components in your code was possible using GridBagLayout, without setting position or size:

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

public class PosicaoDeCompTest {

    public static void main(String args[]) {

        EventQueue.invokeLater(() -> {
            /* Gera os campos, tela, e configurações */
            JFrame frame = new JFrame();
            JPanel panel = new JPanel(new GridBagLayout());

            JTextField texto = new JTextField();
            texto.setColumns(10);
            JComboBox combo = new JComboBox();

            /* Cria as opções e configurações do JComboBox */
            combo.setBackground(Color.WHITE);
            combo.addItem("opção1");
            combo.addItem("opção2");
            combo.addItem("opção3");

            /* Adiciona as coisas na tela */
            panel.add(texto);
            panel.add(combo);

            /* Configurações da janela */
            frame.setSize(500, 500);
            frame.getContentPane().add(panel);

            frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
            frame.setVisible(true);
        });

    }

}

Exit:

Note that managers take care of component size most of the time, so it is not necessary to set fixed values for this, let the layout do this work for you.