您的代码和建议的问题：

>再次，您需要更改组件的preferredSize(这里是Graph JPanel)，而不是大小

>不要设置JFrame的边界。

>在添加组件之后并在调用setVisible(true)之前，在JFrame上调用pack()

>您的foreach循环将不起作用，因为您的ArrayList的大小为0(测试它看到这是正确的)。而是使用从0到10的for循环。

>您不应该在paintComponent(…)方法中使用程序逻辑，而只能绘制代码。所以我将使ArrayList成为一个类变量，并将其填充到类的构造函数内。

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 scores;

public DrawGraph(List 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 graphPoints = new ArrayList();

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 scores = new ArrayList();

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();

}

});

}

}

这将创建一个如下图形：