在进行计算时显示进度条

Question

我正在编写代码以计算Pi的值，有时可能需要很长时间才能计算出。我添加了一个进度条以显示进度，但是代码完全按照我的指示执行，它在计算后打开进度条，然后立即将其关闭（当值达到100时，它会关闭。）我试图粘贴代码对于进度条进入循环，但是不久我意识到解决了该问题，但是创建了多个进度条窗口。如果放在计算之前，进度条将保持为0（很明显），我在下面显示了我的代码：

import java.awt.BorderLayout;
import java.awt.Container;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JProgressBar;
import javax.swing.border.Border;
import java.util.Scanner;

public class PicCalc 
{
public static void main(String args[]) 
{
  Scanner keyboard = new Scanner(System.in);
  double i = 0;
    double stage = 1;
  int iterations = 1;
    int x = 3; //Simply a variable to calculate pi
  double y = -1.0; // Another variable for pi
    double myPi; //This is my calculation of Pi, don't eat it. 

  System.out.println("Hello! I calculate Pi and compare it to the acutal value of Pi!");
  System.out.println("How many iterations?");
  iterations = keyboard.nextInt();

  //Calculates Pi
  for (i = 1.0; i <= iterations; i++)
  {
         stage = stage + y/x;
         y = - y; //Flips Sign
         x+=2; 
  }

    myPi = 4*stage;
    System.out.println("My Pi: " + myPi);
    //STOP CALCULATING PI

    //CALCULATE PERCENT COMPLETE
  double percent = 100*(i/iterations);
  int intPercent = (int) (percent + 0.5); //Adds .5 in order to round.
  //STOP CALCULATING PERCENT COMPLETE

  //MAKES LOADING SCREEN
  JFrame f = new JFrame("Loading...");
  f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  Container content = f.getContentPane();
  JProgressBar progressBar = new JProgressBar();
  progressBar.setValue(intPercent);
  progressBar.setStringPainted(true);
  Border border = BorderFactory.createTitledBorder("Calcualating...");
  progressBar.setBorder(border);
  content.add(progressBar, BorderLayout.NORTH);
  f.setSize(300, 100);
  f.setVisible(true);
  //END OF MAKING LOADING SCREEN

 //CLOSES LOADING SCREEN WHEN 100% IS ACHIEVED
  if (percent >= 100)
  {
     f.dispose();
  }      
  //END OF CLOSING SCREEN HERE

Answer 1

您只有一个线程，因此GUI永远没有机会进行更新（因为它正在忙于计算）。

正常方法是将计算放在后台线程中，以便事件调度线程（EDT）[aka GUI thread]可以自由更新GUI。

请参阅这些以获取一些指导，并且Google会提供更多信息。

您如何使用事件调度线程？

Java背景线程