JAVA无法从另一个类中绘制到JFrame上 [英] JAVA can't paint onto JFrame from within another class

问题描述

我知道这是我的错误。我的问题是为什么这不起作用我错过了什么我可以称之为我把它放在一个方法而不是一个类，所以我假设他们的第三类有问题？

I am aware this is my error. My question is why isn't this working what am i missing i can call this is i put it a method instead of a class so i am assuming theirs something wrong with the third class?

第1类：

package assignment.pkg1.java;

import java.awt.Color;
import javax.swing.JFrame;

public class JVMVeiwer  {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    final int FRAME_WIDTH = 1000; // Frame Width
    final int FRAME_HEIGHT = 800; // Frame Height
    JFrame frame = new JFrame();

    frame.setSize(FRAME_WIDTH, FRAME_HEIGHT); //Sets Frame Size
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setTitle("JVM Diagram");// Sets the Title       
    JVMComponent component = new JVMComponent();
    frame.setBackground(Color.WHITE);
    frame.add(component); // adds the diagram to the JFrame       
    frame.setVisible(true); // Makes the frame visible
}

}

第2类：

package assignment.pkg1.java;

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


public class JVMComponent extends  JComponent { 

@Override
public void  paintComponent(Graphics g) {      
    super.paintComponent(g);        
    Graphics2D g2 = (Graphics2D) g; // recover the graphic  
    JVMDiagram diagram = new JVMDiagram(); // creates an instance of JVM Diagram
    diagram.draw(g2);
  }
}

第3类这是一个不能用于油漆到jframe：

Class 3 this is the one i i cant use o paint to the jframe:

package assignment.pkg1.java;

import java.awt.Color;
import java.awt.Graphics2D;
import javax.swing.JComponent;

public class JVMDiagram {
// Constructor
public JVMDiagram() {

}
// Draw method for shape
public  void draw(Graphics2D g2) {
// Detailed instructions to draw shape
    int x = getWidth();
    int y = getHeight();
    int temp, temp2;
    int width = x / 2;
    int height = x / 2;
    x = (x - width) / 2;
    y= (y - height) / 2; 

    g2.setColor(Color.RED);
    g2.drawOval(x, y, width, height);
    g2.drawRect(x, y, width, height);
    g2.setColor(Color.RED);
    g2.drawLine(x, y, width + x, height + y);
    g2.drawRoundRect(x, y, width, height, y, y);

    g2.drawLine(x + width, y, x, height + y);
}

}

推荐答案

你的问题是你滥用继承。您的JVMDiagram正在扩展JVMComponent，它不应该。是的，您获得了JVMComponent的getWidth（）和getHeight（）方法，但它们并不意味着什么，因为JVMDiagram没有作为组件添加到GUI，不应该作为组件添加，并且它具有0高度和宽度（打印出来）。

Your problem is that you're misusing inheritance. Your JVMDiagram is extending JVMComponent and it shouldn't. Yes, you gain JVMComponent's getWidth() and getHeight() method, but they don't mean anything since JVMDiagram isn't being added to the GUI as a component, shouldn't be added as a component, and it has 0 height and width (print them out).

重新考虑你的设计，不要为此使用继承。而是在需要时将值从一个对象传递到另一个对象。例如，在JVMComponent中创建一个JVMDiagram字段并对其进行初始化。在JVMComponent的paintComponent方法中使用JVMDiagram绘制方法中的Graphics2D传递宽度和高度。

Rethink your design, don't use inheritance for this. Instead pass in values from one object to the other if needed. For instance, create a JVMDiagram field within JVMComponent and initialize it. Pass in the width and height with the Graphics2D in the JVMDiagram draw method in JVMComponent's paintComponent method.

边问题：永远不要调用 repaint（）来自绘画方法或从绘画方法中调用的代码。

Side issue: never call repaint() from within a painting method or from code that is called from within a painting method.

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