JOptionPane在JFrame中顯示的文字

Question

好吧，JOptionPane文本顯示在JFrame窗口中，甚至我的CS教授都不知道爲什麼。這是一個簡單繪製3行的程序，但無論使用哪種編譯器，它都在JFrame窗口中顯示JOptionPane文本。繼承人我的代碼。

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); 
    } 
} 

這裏的結果：

Answer 1

我相信這是因爲你使用JOptionPane.showInputDialog從paintComponent方法裏面發生的事情。這並不是真正意圖完成的任務，並且會給你帶來不少問題。

我會建議從paintComponent方法中拉出該部分，而不是簡單地設置paintComponent引用的對象上的值。

所以，你的代碼會變得這樣的事情：

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 */ 
    } 
} 

這不會想盡組件希望重新繪製的時間來閱讀這些價值觀，並應糾正故障的圖形。

Answer 2

我將JOptionPane從paintComponent中移出。問題立即消失。它必須重寫該組件。我敢打賭，事實上，你可以撥打super()，但我沒有親自測試過這個假設。當你將JOptionPane移到paintComponent之外時，無論是什麼原因，問題都會消失。另外，我覺得用戶可以更容易地告訴用戶輸入座標，然後將這些座標解析成jx，jy等變量。簡單，只有三個窗格，而不是六個。

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); 
    } 
}