在JFrame

Question

好的，JOptionPane窗口中显示了JFrame文字，即使是我的CS教授也无法找出原因。这是一个简单绘制3行的程序，但无论我使用哪种编译器，它都会在JFrame窗口中显示JOptionPane文本。这是我的代码。

import java.awt.Graphics;
import javax.swing.*;
import javax.swing.JFrame;
public class Lab5_1 extends JPanel {

    public void paintComponent( Graphics g ) {

        super.paintComponent(g);

        String ia = JOptionPane.showInputDialog ("Enter the beginning  x point of the line");
        String iab = JOptionPane.showInputDialog ("Enter the beginning y point of the line");
        String ja = JOptionPane.showInputDialog ("Enter the end  x point of the line");
        String jab = JOptionPane.showInputDialog ("Enter the end y point of the line");
        int jx = Integer.parseInt(ja);
        int jy = Integer.parseInt(jab);
        int ix = Integer.parseInt(ia);
        int iy = Integer.parseInt(iab);

        String iac = JOptionPane.showInputDialog ("Enter the beginning  x point of the line");
        String iabc = JOptionPane.showInputDialog ("Enter the beginning y point of the line");
        String jac = JOptionPane.showInputDialog ("Enter the end  x point of the line");
        String jabc = JOptionPane.showInputDialog ("Enter the end y point of the line");
        int jxb = Integer.parseInt(jac);  
        int jyb = Integer.parseInt(jabc);
        int ixb = Integer.parseInt(iac);
        int iyb = Integer.parseInt(iabc);

        String iad = JOptionPane.showInputDialog ("Enter the beginning  x point of the line");
        String iabd = JOptionPane.showInputDialog ("Enter the beginning y point of the line");
        String jad = JOptionPane.showInputDialog ("Enter the end  x point of the line");
        String jabd = JOptionPane.showInputDialog ("Enter the end y point of the line");
        int jxc = Integer.parseInt(jad);
        int jyc = Integer.parseInt(jabd);
        int ixc = Integer.parseInt(iad);
        int iyc = Integer.parseInt(iabd);

        g.drawLine(ix,iy,jx,jy);
        g.drawLine(ixb,iyb,jxb,jyb);
        g.drawLine(ixc,iyc,jxc,jyc);
    }

    public static void main( String[] args ) {
        Lab5_1 panel = new Lab5_1(); 
        JFrame application = new JFrame(); 

        application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        application.add( panel ); 
        application.setSize( 500, 290 ); 
        application.setVisible( true ); 
    }
}

结果如下：

Answer 1

我相信这种情况正在发生，因为您正在JOptionPane.showInputDialog方法内部使用paintComponent。这并不是真正意图完成的，并且会给你带来不小的问题。

我建议将该部分从paintComponent方法中拉出来，而只需在paintComponent引用的对象上设置值。

所以你的代码会变成这样：

public class Lab5_1 extends JPanel {
    int ix;
    /* Rest of the fields */

    public void paintComponent( Graphics g ) {
        super.paintComponent(g);

        g.drawLine(ix,iy,jx,jy);
        /* Rest of the lines */
    }

    public static void main(String[] args){
        Lab5_1 panel = new Lab5_1();
        String ia = JOptionPane.showInputDialog ("Enter the beginning  x point of the line");
        panel.ix = Integer.parseInt(ia);

        /* Rest of your initialization code */
    }
}

每次想要重新绘制组件时，都不会尝试读取这些值，并且应该纠正图形故障。

Answer 2

我将JOptionPane移出了paintComponent方法。问题立即消失了。它必须做一些事情来覆盖该组件。我的赌注是你在覆盖中调用super()，但我自己没有测试过这个假设。当你将JOptionPane移到paintComponent之外时，无论其原因是什么问题都会消失。

另外，我觉得用户告诉用户输入坐标，然后将这些坐标解析为jx，jy等变量会更容易。更简单，只有三个窗格，而不是六个。

import java.awt.Graphics;

import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class Lab5_1 extends JPanel {

    private static final long serialVersionUID = 1L;

    private static int jx;
    private static int jy;
    private static int ix;
    private static int iy;
    private static int jxb;
    private static int jyb;
    private static int ixb;
    private static int iyb;
    private static int jxc;
    private static int jyc;
    private static int ixc;
    private static int iyc;

    @Override public void paintComponent(Graphics g) {

        super.paintComponent(g);

        g.drawLine(ix, iy, jx, jy);
        g.drawLine(ixb, iyb, jxb, jyb);
        g.drawLine(ixc, iyc, jxc, jyc);

    }

    public static void main(String[] args) {
        SwingTesting panel = new SwingTesting();
        JFrame application = new JFrame();

        String ia = JOptionPane.showInputDialog("Enter the beginning  x point of the line");
        String iab = JOptionPane.showInputDialog("Enter the beginning y point of the line");
        String ja = JOptionPane.showInputDialog("Enter the end  x point of the line");
        String jab = JOptionPane.showInputDialog("Enter the end y point of the line");
        jx = Integer.parseInt(ja);
        jy = Integer.parseInt(jab);
        ix = Integer.parseInt(ia);
        iy = Integer.parseInt(iab);

        String iac = JOptionPane.showInputDialog("Enter the beginning  x point of the line");
        String iabc = JOptionPane.showInputDialog("Enter the beginning y point of the line");
        String jac = JOptionPane.showInputDialog("Enter the end  x point of the line");
        String jabc = JOptionPane.showInputDialog("Enter the end y point of the line");
        jxb = Integer.parseInt(jac);
        jyb = Integer.parseInt(jabc);
        ixb = Integer.parseInt(iac);
        iyb = Integer.parseInt(iabc);

        String iad = JOptionPane.showInputDialog("Enter the beginning  x point of the line");
        String iabd = JOptionPane.showInputDialog("Enter the beginning y point of the line");
        String jad = JOptionPane.showInputDialog("Enter the end  x point of the line");
        String jabd = JOptionPane.showInputDialog("Enter the end y point of the line");
        jxc = Integer.parseInt(jad);
        jyc = Integer.parseInt(jabd);
        ixc = Integer.parseInt(iad);
        iyc = Integer.parseInt(iabd);

        application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        application.add(panel);
        application.setSize(500, 290);
        application.setVisible(true);
    }
}