编写程序模拟用以表示直线的Line类，具体包含以下逻辑： ① 表示直线起点和终点的嵌套类Point，其包含描述横纵坐标的x、y字段。 ② 表示直线方向的嵌套枚举Direction，其包含描述若干方向的枚举常量。 在Line类中编写必要的代码，然后在测试类LineTest中构造几个Line对象并输出每个对象的有关信息。

好的，以下是 Line 类的代码实现：

public class Line {
    // 嵌套类：表示直线上的点
    public static class Point {
        private double x;
        private double y;
        
        public Point(double x, double y) {
            this.x = x;
            this.y = y;
        }
        
        public double getX() {
            return x;
        }
        
        public double getY() {
            return y;
        }
    }
    
    // 嵌套枚举类：表示直线的方向
    public enum Direction {
        HORIZONTAL, // 水平
        VERTICAL,   // 垂直
        DIAGONAL    // 对角线
    }
    
    private Point startPoint;
    private Point endPoint;
    private Direction direction;
    
    public Line(Point startPoint, Point endPoint) {
        this.startPoint = startPoint;
        this.endPoint = endPoint;
        if (startPoint.getX() == endPoint.getX()) {
            direction = Direction.VERTICAL;
        } else if (startPoint.getY() == endPoint.getY()) {
            direction = Direction.HORIZONTAL;
        } else {
            direction = Direction.DIAGONAL;
        }
    }
    
    public Point getStartPoint() {
        return startPoint;
    }
    
    public Point getEndPoint() {
        return endPoint;
    }
    
    public Direction getDirection() {
        return direction;
    }
    
    @Override
    public String toString() {
        return "Line [startPoint=" + startPoint.getX() + "," + startPoint.getY() + 
                ", endPoint=" + endPoint.getX() + "," + endPoint.getY() +
                ", direction=" + direction + "]";
    }
}

然后我们在测试类 LineTest 中构造几个 Line 对象并输出每个对象的信息：

public class LineTest {
    public static void main(String[] args) {
        Line line1 = new Line(new Line.Point(1, 2), new Line.Point(3, 2));
        Line line2 = new Line(new Line.Point(1, 2), new Line.Point(3, 4));
        Line line3 = new Line(new Line.Point(1, 2), new Line.Point(1, 4));
        
        System.out.println(line1);
        System.out.println(line2);
        System.out.println(line3);
    }
}

运行结果：

Line [startPoint=1.0,2.0, endPoint=3.0,2.0, direction=HORIZONTAL]
Line [startPoint=1.0,2.0, endPoint=3.0,4.0, direction=DIAGONAL]
Line [startPoint=1.0,2.0, endPoint=1.0,4.0, direction=VERTICAL]

可以看到，每个 Line 对象都能正确地输出其起点、终点和方向。