关于MyRectangle、MyCircle及MySquare类containsPoint方法的技术咨询

Let’s break this down step by step to clear up your confusion, then fix your MySquare implementation.

First, the core purpose of the containsPoint method: it checks whether a given point (defined by xValue and yValue) lies inside or on the boundary of the shape instance. Let’s walk through the existing class logic first, then tackle your square code.

1. Why does MyRectangle.containsPoint work the way it does? #

Your rectangle is defined with:

• x, y: The coordinates of its top-left corner (assuming your grid uses a standard top-left origin)
• width: Horizontal length of the rectangle
• height: Vertical length of the rectangle

To confirm a point is inside this rectangle, we need two conditions to be true:

• The point’s x-coordinate (xValue) falls between the rectangle’s left edge (x) and right edge (x + width)
• The point’s y-coordinate (yValue) falls between the rectangle’s top edge (y) and bottom edge (y + height)

The line return xValue >= x && xValue <= x + width && yValue >= y && yValue <= y + height; is a boolean expression—all those int comparisons evaluate to true or false, and the && (logical AND) combines them into a single boolean result. That’s why using int values here is totally valid—it still produces the required boolean return type.

2. What’s the logic behind MyCircle.containsPoint? #

For circles, we rely on the distance formula to check if a point is within the circle’s bounds:

• x, y: Coordinates of the circle’s center
• radius: Radius of the circle

Here’s the breakdown:

1. Calculate the horizontal gap between the point and the center: dx = x - xValue (the sign doesn’t matter because we’ll square it next)
2. Calculate the vertical gap: dy = y - yValue
3. Use the Pythagorean theorem to find the straight-line distance between the two points: distance = sqrt(dx² + dy²)
4. If this distance is less than or equal to the radius, the point is inside or on the edge of the circle.

Again, the final comparison distance <= radius evaluates to a boolean, which matches the method’s return type.

3. Correcting MySquare.containsPoint #

A square is just a rectangle where width and height are equal (both equal to side). You can reuse the same boundary-checking logic as MyRectangle, replacing width and height with side.

Here’s the fixed MySquare class:

public class MySquare extends GridItem {
    private int side;

    public MySquare(int xValue, int yValue, int s) {
        x = xValue;
        y = yValue;
        side = s;
    }

    @Override
    public double getArea() {
        return side * side;
    }

    @Override
    public boolean containsPoint(int xValue, int yValue) {
        // Check if the point falls within the square's boundaries
        return xValue >= x && xValue <= x + side && yValue >= y && yValue <= y + side;
    }
}

This works because:

• The square’s left edge is at x, right edge at x + side
• The square’s top edge is at y, bottom edge at y + side
• Only points that meet both x-range and y-range conditions are considered inside the square.

内容的提问来源于stack exchange，提问作者user8974164