Class extends JFrame - nefunguji gettry – Java – Fórum – Programujte.com

Ahoj, snazim se udelat jednoduche kreslitko.

Trida imgPanel je potomkem tridy javax.swing.JPanel a prekryva metodu paintComponent:

package gui;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import javax.swing.JPanel;

public class imgPanel extends JPanel{

	private BufferedImage buffer;
	private int sirka;
	private int vyska;
	
	public imgPanel() {
		sirka = 200;
		vyska = 200;
		buffer = new BufferedImage(sirka, vyska, BufferedImage.TYPE_3BYTE_BGR);
	}

	@Override
	public void paintComponent(Graphics g) {
        prepareImage();
        g.drawImage(buffer, 0, 0, null);
        g.dispose();
    }
    private void prepareImage() {
        Graphics g = buffer.createGraphics();
        g.drawLine(5, 5, 20, 50);
        g.setColor(Color.BLUE);
        g.dispose();
    }
    
    public int getSirka() {
		return sirka;
	}    
    public void setSirka(int sirka) {
		this.sirka = sirka;
	}    
    public int getVyska() {
		return vyska;
	}    
    public void setVyska(int vyska) {
		this.vyska = vyska;
	}        
}

A trida Okno pak pomoci JPanelu z tridy imgOkno zobrazi jednoduche kreslitko:

package gui;

import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;

public class Okno extends JFrame {

	private JPanel contentPane;
	private JPanel abc;
	
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					Okno frame = new Okno();
					frame.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	public Okno() {
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setBounds(100, 100, 450, 300);
		contentPane = new JPanel();
		contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
		contentPane.setLayout(new BorderLayout(0, 0));
		setContentPane(contentPane);
		
		abc = new imgPanel();	
	/* System.out.println(abc.getVyska); */
		contentPane.add(abc, BorderLayout.CENTER);      
	}
}

Kdyz se ale snazim v tride Okno zavolat metodu tridy imgPanel getVyska(), tak program vzdy spadne pri kompilaci.

Nevite, cim to muze byt?

Urobil si iba chybu pri inicializacii atributu abc.

mas: private JPanel abc;

ma byt: private imgPanel abc;

Preco? To, ze trieda imgPanel dedi od triedy JPanel znamena, ze moze vyuzit vsetku jej funkcionalitu, no naopak to neplati. Cize ked si zadefinoval, ze atribut abc bude typu JPanel, poskytol si jej funkcionalitu iba samotneho JPanelu a pozadovana metodka getVyska() je v oddedenej triede imgPanel.