编写一个java语言的导出dxf格式的程序

下面是一个简单的Java程序，可以导出DXF格式的文件：

import java.io.*;
import java.util.*;

public class DXFExporter {

    private BufferedWriter writer;
    private int entityCount = 0;

    public void exportToFile(String filename, List<Entity> entities) throws IOException {
        writer = new BufferedWriter(new FileWriter(filename));
        writeHeader();
        writeEntities(entities);
        writeFooter();
        writer.close();
    }

    private void writeHeader() throws IOException {
        writer.write("0\nSECTION\n");
        writer.write("2\nHEADER\n");
        writer.write("9\n$ACADVER\n");
        writer.write("1\nAC1009\n");
        writer.write("0\nENDSEC\n");
    }

    private void writeEntities(List<Entity> entities) throws IOException {
        writer.write("0\nSECTION\n");
        writer.write("2\nENTITIES\n");
        for (Entity entity : entities) {
            writeEntity(entity);
        }
        writer.write("0\nENDSEC\n");
    }

    private void writeFooter() throws IOException {
        writer.write("0\nEOF\n");
    }

    private void writeEntity(Entity entity) throws IOException {
        entityCount++;
        writer.write("0\n" + entity.getType() + "\n");
        writer.write("5\n" + entityCount + "\n");
        writer.write("8\n0\n");
        entity.writeData(writer);
    }
}

abstract class Entity {

    public abstract String getType();

    public abstract void writeData(BufferedWriter writer) throws IOException;
}

class Line extends Entity {

    private double x1, y1, x2, y2;

    public Line(double x1, double y1, double x2, double y2) {
        this.x1 = x1;
        this.y1 = y1;
        this.x2 = x2;
        this.y2 = y2;
    }

    public String getType() {
        return "LINE";
    }

    public void writeData(BufferedWriter writer) throws IOException {
        writer.write("10\n" + x1 + "\n");
        writer.write("20\n" + y1 + "\n");
        writer.write("11\n" + x2 + "\n");
        writer.write("21\n" + y2 + "\n");
    }
}

// Add more entity classes here, such as Circle, Arc, etc.

你可以使用这个程序来创建 `Line` 对象，然后将它们添加到一个 `List<Entity>` 中，最后调用 `exportToFile()` 方法导出DXF文件。例如：

List<Entity> entities = new ArrayList<Entity>();
entities.add(new Line(0, 0, 10, 10));
entities.add(new Line(0, 10, 10, 0));
DXFExporter exporter = new DXFExporter();
exporter.exportToFile("output.dxf", entities);

注意：这只是一个简单的示例程序，你需要根据你的具体需求进行修改和扩展。