Java日志第50天 2020.8.26

例4.6 编写一个程序，用来求两个整数或3个整数中的最大数。如果输入两个整数，程序就输出这两个整数中的最大数，如果输入3个整数，程序就输出这3个整数中的最大数。

public class Demo4_6 {
    public static void main(String[] args) {
        int a=8, b=-12, c=27;
        System.out.println("max(a, b, c) = "+max(a,b,c));
        System.out.println("max(a, b) = "+max(a,b));
    }

    public static int max(int a, int b, int c) {
        if(b>a)
            a = b;
        if (c>a)
            a = c;
        return a;
    }
    
    public static int max(int a, int b) {
        return a > b ? a : b;
    }
}

 

 

例4.7 将例4.6程序改为通过函数模板来实现

 

例4.8 求2个或3个正整数中的最大数，用带有默认参数的函数实现

Java不能设置默认参数，只能通过重载来实现。

 

 

例4.9 用弦截法求方程f(x)=x³-5x²+16x-80=0的根

 

 

import java.util.Scanner;

public class Demo4_9 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double x1, x2, f1, f2, x;
        do {
            System.out.print("Input x1, x2:");
            x1 = sc.nextDouble();
            x2 = sc.nextDouble();
            f1 = f(x1);
            f2 = f(x2);
        } while (f1*f2>=0);
        x = root(x1, x2);

        System.out.println("A root of equation is "+x);
    }

    private static double f(double x) {
        double y;
        y = x*x*x-5*x*x+16*x-80;
        return y;
    }

    private static double xpoint(double x1,double x2) {
        double y;
        y = (x1*f(x2)-x2*f(x1))/(f(x2)-f(x1));
        return y;
    }

    private static double root(double x1, double x2) {
        double x,y,y1;
        y1=f(x1);
        do {
            x = xpoint(x1,x2);
            y = f(x);
            if (y*y1>0){
                y1 = y;
                x1 = x;
            } else
                x2 = x;
        } while (Math.abs(y)>=0.00001);
        return x;
    }
}