用Java绘制简单的折线图

你的代码存在问题和建议：

• 同样，你需要更改组件的preferredSize（在这里为Graph JPanel），而不是大小
• 不要设置Jframe的边界。
• 呼叫

  pack()

  你的Jframe将组件添加到它后并调用调用setVisible之前（真）
• 由于ArrayList的大小为0，因此你的foreach循环将不起作用（对其进行测试以确保它是正确的）。而是使用从0到10的for循环。
• 你的

  paintComponent(...)

  方法内部不应包含程序逻辑，而应仅绘制代码。因此，我将ArrayList设为一个类变量，并将其填充到该类的构造函数中。
  例如：
  

import java.awt.BasicStroke;import java.awt.Color;import java.awt.Dimension;import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.Point;import java.awt.RenderingHints;import java.awt.Stroke;import java.util.ArrayList;import java.util.List;import java.util.Random;import javax.swing.*;@SuppressWarnings("serial")public class DrawGraph extends JPanel {   private static final int MAX_SCORE = 20;   private static final int PREF_W = 800;   private static final int PREF_H = 650;   private static final int BORDER_GAP = 30;   private static final Color GRAPH_COLOR = Color.green;   private static final Color GRAPH_POINT_COLOR = new Color(150, 50, 50, 180);   private static final Stroke GRAPH_STROKE = new BasicStroke(3f);   private static final int GRAPH_POINT_WIDTH = 12;   private static final int Y_HATCH_CNT = 10;   private List<Integer> scores;   public DrawGraph(List<Integer> scores) {      this.scores = scores;   }   @Override   protected void paintComponent(Graphics g) {      super.paintComponent(g);      Graphics2D g2 = (Graphics2D)g;      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);      double xScale = ((double) getWidth() - 2 * BORDER_GAP) / (scores.size() - 1);      double yScale = ((double) getHeight() - 2 * BORDER_GAP) / (MAX_SCORE - 1);      List<Point> graphPoints = new ArrayList<Point>();      for (int i = 0; i < scores.size(); i++) {         int x1 = (int) (i * xScale + BORDER_GAP);         int y1 = (int) ((MAX_SCORE - scores.get(i)) * yScale + BORDER_GAP);         graphPoints.add(new Point(x1, y1));      }      // create x and y axes       g2.drawLine(BORDER_GAP, getHeight() - BORDER_GAP, BORDER_GAP, BORDER_GAP);      g2.drawLine(BORDER_GAP, getHeight() - BORDER_GAP, getWidth() - BORDER_GAP, getHeight() - BORDER_GAP);      // create hatch marks for y axis.       for (int i = 0; i < Y_HATCH_CNT; i++) {         int x0 = BORDER_GAP;         int x1 = GRAPH_POINT_WIDTH + BORDER_GAP;         int y0 = getHeight() - (((i + 1) * (getHeight() - BORDER_GAP * 2)) / Y_HATCH_CNT + BORDER_GAP);         int y1 = y0;         g2.drawLine(x0, y0, x1, y1);      }      // and for x axis      for (int i = 0; i < scores.size() - 1; i++) {         int x0 = (i + 1) * (getWidth() - BORDER_GAP * 2) / (scores.size() - 1) + BORDER_GAP;         int x1 = x0;         int y0 = getHeight() - BORDER_GAP;         int y1 = y0 - GRAPH_POINT_WIDTH;         g2.drawLine(x0, y0, x1, y1);      }      Stroke oldStroke = g2.getStroke();      g2.setColor(GRAPH_COLOR);      g2.setStroke(GRAPH_STROKE);      for (int i = 0; i < graphPoints.size() - 1; i++) {         int x1 = graphPoints.get(i).x;         int y1 = graphPoints.get(i).y;         int x2 = graphPoints.get(i + 1).x;         int y2 = graphPoints.get(i + 1).y;         g2.drawLine(x1, y1, x2, y2);    }      g2.setStroke(oldStroke); g2.setColor(GRAPH_POINT_COLOR);      for (int i = 0; i < graphPoints.size(); i++) {         int x = graphPoints.get(i).x - GRAPH_POINT_WIDTH / 2;         int y = graphPoints.get(i).y - GRAPH_POINT_WIDTH / 2;;         int ovalW = GRAPH_POINT_WIDTH;         int ovalH = GRAPH_POINT_WIDTH;         g2.fillOval(x, y, ovalW, ovalH);      }   }   @Override   public Dimension getPreferredSize() {      return new Dimension(PREF_W, PREF_H);   }   private static void createAndShowGui() {      List<Integer> scores = new ArrayList<Integer>();      Random random = new Random();      int maxDataPoints = 16;      int maxScore = 20;      for (int i = 0; i < maxDataPoints ; i++) {         scores.add(random.nextInt(maxScore));      }      DrawGraph mainPanel = new DrawGraph(scores);      Jframe frame = new Jframe("DrawGraph");      frame.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);      frame.getContentPane().add(mainPanel);      frame.pack();      frame.setLocationByPlatform(true);      frame.setVisible(true);   }   public static void main(String[] args) {      SwingUtilities.invokeLater(new Runnable() {         public void run() { createAndShowGui();         }      });   }}