把两个问题合成一个！求……

合成一个？圆是二维的，点是三维的，是不是要问在不在球内？

import java.util.Scanner;

public class Point {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入点的X坐标：");
        int x = scanner.nextInt();
        System.out.print("请输入点的Y坐标：");
        int y = scanner.nextInt();
        System.out.print("请输入点的Z坐标：");
        int z = scanner.nextInt();
        Point p = new Point(x, y, z);
        System.out.println("该点(" + x + "," + y + "," + z + ")距离原点：" + p.length());
        System.out.println("该点(" + x + "," + y + "," + z + ")距离原点的平方为：" + p.length() * p.length());
    }

    public Point(int x, int y, int z) {
        this.x = x;
        this.y = y;
        this.z = z;
    }

    public int length() {
        return length(new Point(0, 0, 0));
    }

    public int length(Point p) {
        int lx = Math.abs(x - p.getX());
        int ly = Math.abs(y - p.getY());
        int lz = Math.abs(z - p.getZ());
        return (int) Math.sqrt((lx * lx) + (ly * ly) + (lz * lz));
    }

    private int x;
    private int y;
    private int z;

    public int getX() {
        return x;
    }


    public int getY() {
        return y;
    }


    public int getZ() {
        return z;
    }
}

仅供参考，不要照抄。
第一个图片，没有描述圆是个什么圆！
大概思路 求出圆的中心点、半径。
如果点距离中心点的距离小于半径则在圆内，否则则不在！