getPreferredSize() works on JFrame; why doesn't it work on Frame?

Question

I hope to get some help for a problem that confuses me.

I tested getPreferredSize() on Frame and on Frame. In Frame, getPreferredSize() returns all 0 (both width and height), while in Frame, it returns non-zero numbers, which is working.

I am not sure which part of my coding in nolayout() method such that getPreferredSize() simply returns 0, and isPreferredSizeSet() returns FALSE, which implies preferred size is not set.

Why is it not set? Can anyone help? Thanks.

Below are the codings of this simple test program.

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

public class test {
public test(){
    JFrame frame = new JFrame("AbsoluteLayoutDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    Container p = frame.getContentPane();
    p.setLayout(null);
    JButton b1 = new JButton("one");
    p.add(b1);
    Dimension size = b1.getPreferredSize();
    System.out.println("size width is "+size.width+" height is "+size.height);
    JLabel label2 = new JLabel("Text-Only Label");
    p.add(label2);
    size = label2.getPreferredSize();
    System.out.println("label size width is "+size.width+" height is "+size.height);

    Insets insets = p.getInsets(); 
    frame.setSize(300 + insets.left + insets.right, 125 + insets.top + insets.bottom);
    frame.setVisible(true);
}
public static void main(String[] args) {
    test t = new test();
    nolayout();
}enter code here



public static void nolayout() {

    Frame f = new Frame();
    f.setLayout(null);

    Insets its = f.getInsets();

    System.out.println("its left, "+its.left+" right, "+its.right+" top "+its.top+" bottom "+its.bottom);

    f.setLocation(200, 100 );
    f.setSize(its.left+its.right+300,its.top+its.bottom+200);

    Label l1 = new Label("Enter Integer to be added : ",Label.RIGHT);
    TextField t1 = new TextField("0",10);

    f.add(l1);
    f.add(t1);


    System.out.println("is l1 preferred size set "+l1.isPreferredSizeSet());
    Dimension sz = l1.getPreferredSize();
    l1.setBounds(its.left + 10, its.top + 10, sz.width, sz.height);
    System.out.println("label 1 width "+sz.width+" height " +sz.height);

    sz = t1.getPreferredSize();
    t1.setBounds(its.left + 100, its.top + 10, sz.width, sz.height);
    System.out.println("Text 1 width "+sz.width+" height " +sz.height);

    f.setVisible(true);
    }
}

The output on the command window is as follows:

C:\JAVAPR>java test
size width is 55 height is 26
label size width is 88 height is 16
its left, 0 right, 0 top 0 bottom 0
is l1 preferred size set false
label 1 width 0 height 0
Text 1 width 0 height 0 enter code here

`p.setLayout(null);` 1) Java GUIs have to work on different OS', screen size, screen resolution etc. using different PLAFs in different locales. As such, they are not conducive to pixel perfect layout. Instead use layout managers, or [combinations of them](http://stackoverflow.com/a/5630271/418556) along with layout padding and borders for [white space](http://stackoverflow.com/a/17874718/418556). 2) See [Detection/fix for the hanging close bracket of a code block](http://meta.stackexchange.com/q/251795/155831) for a problem I could no longer be bothered fixing. — Andrew Thompson, May 28 '16 at 14:18
*"..why doesn't it work on Frame?"* It's AWT based, so I don't see anybody (at least besides you) wondering about it. — Andrew Thompson, May 28 '16 at 14:20
Quit crossposting: http://www.coderanch.com/t/666218/java/java/getPreferredSize-works-JFrame-doesn-work — camickr, May 28 '16 at 15:08

score 1 · Answer 1 · edited May 23 '17 at 12:24

The result of getPreferredSize() is reliable, once you specify a layout and pack() the parent Window. As suggested here, you may want to override getPreferredSize().

import java.awt.Dimension;
import java.awt.Frame;
import java.awt.GridBagLayout;
import java.awt.Label;
import java.awt.Panel;
import java.awt.TextField;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

/** @see https://stackoverflow.com/posts/37501391/edit */
public class Test {

    private void display() {
        Frame f = new Frame(){
            @Override
            public Dimension getPreferredSize() {
                return new Dimension(320, 240);
            }
        };
        f.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        f.setLayout(new GridBagLayout());
        Panel p = new Panel();
        p.add(new Label("Test", Label.RIGHT));
        p.add(new TextField("Test", 10));
        f.add(p);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        new Test().display();
    }
}

getPreferredSize() works on JFrame; why doesn't it work on Frame?

1 Answers1