11 JavaAPI之lang的几个小程序

/*写一个方法统计出一个字符串中，数字的个数、空格的个数、
小写英文字母的个数、大写英文字母的个数等。*/
class Census {
    String str;
    int num ;
    int chs ;
    int upcase ;
    int lowcase ;
    public Census() {}
    public Census(String str) {
        this();
        this.str = str;
    }
    public int GetChar(){
        char[] ch = str.toCharArray();
        for (int i = 0; i < ch.length; i++) {
            if (Character.isLetter(ch[i])) {
                chs++;
            };
            
        }
        return chs;
    }
    public int GetNum(){
        char[] ch = str.toCharArray();
        for (int i = 0; i < ch.length; i++) {
            char c = ch[i];
            if (Character.isDigit(ch[i])) {
                num++;
            };
        }
        return num;
    }
    public int GetUpCase(){
        char[] ch = str.toCharArray();
        for (int i = 0; i < ch.length; i++) {
            char c = ch[i];
            if (Character.isUpperCase(ch[i])) {
                upcase++;
            };
        }
        return upcase;
    }
    public int GetLowCase(){
        char[] ch = str.toCharArray();
        for (int i = 0; i < ch.length; i++) {
            char c = ch[i];
            if (Character.isLowerCase(ch[i])) {
                lowcase++;
            };
        }
        return lowcase;
    }
    @Override
    public String toString() {
        return "str=" + str + ", 数字的个数=" + this.GetNum() + ", 字符的个数=" + this.GetChar()
                + ", 大写字母的个数=" + this.GetUpCase() + ", 小写字母的个数=" + this.GetLowCase() ;
    }
    
    
    
}

public class CensusTest{
    public static void main(String[] args) {
        Census a = new Census("78uijkIIOreY228");
        System.out.println(a.toString());
            
    }
}

计算一个圆面积和周长还有圆心到原点的距离。

class Point {            //定义Point类
    double x;
    double y;
    double z;
    public Point(){}
    public Point(double x, double y, double z) {
        this();
        this.x = x;
        this.y = y;
        this.z = z;
    }
    
    @Override
    public String toString() {
        return "Point [x=" + x + ", y=" + y + ", z=" + z + "]";
    }
    public double distanceOfo(){
        return Math.sqrt(x*x+y*y+z*z);
    }
}

public class PointTest{
    public static void main(String[] args) {
        Point a = new Point(15,19,23);
        System.out.println(a.distanceOfo());         //输出double 类型点到原点距离
        System.out.println(String.format("%.2f",(a.distanceOfo())));    //输出小数位后两位
    }
}

class Circle extends Point{        //定义一个子类Circle 父类是Point
    double radius;
    public Circle(){}
    public Circle(double x, double y, double z,double radius) {
        super(x,y,z);
        this.radius = radius;
    }
    public double getPerimeter(){    //计算周长
        return (Math.PI*radius*2);
    }
    public double getArea(){
        return (Math.PI*radius*radius);    //计算面积
    }
    
    
}

public class CircleTest {

    public static void main(String[] args) {
        Circle a = new Circle(10,20,32,25);
        System.out.println(a.toString()+"坐标点的圆面积==>"+a.getArea());
        System.out.println(a.toString()+"坐标点的圆周长==>"+a.getPerimeter());
    }

}

使用一行代码计算大数阶乘

 

import java.math.BigInteger;
import java.util.Scanner;

public class Factorial {
    public static BigInteger fac(int n){
        return  (n == 1 ? new BigInteger(""+1):new BigInteger(""+n).multiply(fac(n-1)));
    }
    public static void main(String[] args) {
        Scanner a = new Scanner(System.in);
        System.out.println("请输入一个数");
        int scr = a.nextInt();
        System.out.println(scr+"的阶乘=="+fac(scr));
        
    }
}