line.java

我在学习JAVA的讲义

public class Line    //用到前面的 Point 类
{   
    private Point p0;        //a point on the line
    private double m;      //the slope of the line

    public Line(Point p,double s)
    {   p0=p;
        m=s;
    }

    public double slope( )
    {   return m;
    }

    public double yIntercept( )
    {   return(p0.y( )-m*p0.x( ));
    }

    public boolean equals(Line line)
    {   return (slope( )==line.slope( )&&yIntercept( )==line.yIntercept( ));
    }

    public String toString( )
    {   return new String("y="+(float)m+"x+"+(float)yIntercept( ));
    }

    public static void main(String args[ ])
    {   Point p=new Point(5,-4);
        Line line1=new Line(p,-2);
        System.out.println("\nThe equation of the line 1 is "+line1);
        System.out.println("Its slope is "+line1.slope( )+" and its y-intercept is "+line1.yIntercept( ));
        Line line2=new Line(p,-1);
        System.out.println("\nThe equation of the line 2 is "+line2);
        System.out.println("Ite slope is "+line2.slope( )+" and its y-intercept is "+line2.yIntercept( ));
        if(line2.equals(line1)) System.out.println("They are equal.");
        else System.out.println("They are not equal.");
        Point q=new Point(2,2);
        line2=new Line(q,-2);
        System.out.println("\nThe equation of the line 2 is "+line2);
        System.out.println("Its slope is "+line2.slope( )+" and its y-intercept is "+line2.yIntercept( ));
        if(line2.equals(line1)) System.out.println("They are equal.");
        else System.out.println("They are not equal.");
    }
}