Day6：Java方法详解、命令行传参、可变参数、递归、作业计算器

package com.jiao.method;

public class Demo01 {
    //main方法
    public static void main(String[] args) {

        //实际参数：实际调用传递给他的参数
        int sum = add(1, 2);
        System.out.println(sum);
//        test();
    }

    //加法
    //形式参数，用来定义作用的
    

    public static int add(int a, int b) {
        return a + b;
    }

    public static void test() {
        for (int i = 0; i <= 1000; i++) {
            if (i % 5 == 0) {
                System.out.print(i + "t");
            }
            if (i % (5 * 3) == 0) {
                //System.out.println(); 也可以实现
                System.out.println("n");
            }
        }
    }
}

注：Java是值传递

//方法调用
package com.jiao.method;

public class Demo02 {
    public static void main(String[] args) {
        int max = max(10, 10);
        System.out.println(max);

    }

    //比大小
    //方法
    public static int max(int num1,int num2){

        int result = -1;
        if (num1 == num2){
            System.out.println("num1 == num2");
            return 0; //终止方法
        }
        if (num1 > num2){
            result = num1;
        }else {
            result = num2;
        }
        return result;
    }
}

package com.jiao.method;

public class Demo02 {
    public static void main(String[] args) {
        int max = max(10, 20);
        System.out.println(max);

    }

    //比大小
    public static int max(int num1,int num2){

        int result = -1;
        if (num1 == num2){
            System.out.println("num1 == num2");
            return 0; //终止方法
        }
        if (num1 > num2){
            result = num1;
        }else {
            result = num2;
        }
        return result;
    }
    public static double max(double num1,double num2){

        double result = -1;
        if (num1 == num2){
            System.out.println("num1 == num2");
            return 0; //终止方法
        }
        if (num1 > num2){
            result = num1;
        }else {
            result = num2;
        }
        return result;
    }
}

package com.jiao.method;

public class Demo03 {
    public static void main(String[] args) {
        //args.length 数组长度
        for (int i = 0; i < args.length; i++) {
            System.out.println("args[" + i + "]: " + args[i]);
        }
    }
}
命令行操作如下：
Microsoft Windows [版本 10.0.22000.493]
(c) Microsoft Corporation。保留所有权利。

D:IDEAideaPrejectjavaSE基础语法srccomjiaomethod>javac Demo03.java

D:IDEAideaPrejectjavaSE基础语法srccomjiaomethod>java Demo03
错误: 找不到或无法加载主类 Demo03

D:IDEAideaPrejectjavaSE基础语法srccomjiaomethod>cd ../

D:IDEAideaPrejectjavaSE基础语法srccomjiao>cd ../

D:IDEAideaPrejectjavaSE基础语法srccom>cd ../

D:IDEAideaPrejectjavaSE基础语法src>java com.jiao.method.Demo03

D:IDEAideaPrejectjavaSE基础语法src>java com.jiao.method.Demo03 this is liming
args[0]: this
args[1]: is
args[2]: liming

D:IDEAideaPrejectjavaSE基础语法src>
**注**：cd ../  返回上一级

package com.jiao.method;

public class Demo04 {
    public static void main(String[] args) {
        Demo04 demo04 = new Demo04(); // new一个类
        demo04.test(1); // 调用它


    }
    public void test(int... i){
        System.out.println(i[0]);
    }
}

package com.jiao.method;
//递归思想 求阶乘
public class Demo06 {
    public static void main(String[] args) {
        System.out.println(f(3));

    }
    public static int f(int n){

        if (n == 1){
            return 1;
        }else{
            return n*f(n - 1);
        }
    }
}

递归思想分析（引出“栈”概念）

注：能不用就别用，会压好多“栈”，会占用过多内存，影响机器性能。

package com.jiao.method;


import java.util.Scanner;

public class Test01 {
    public static void main(String[] args) {
        System.out.println("请输入第一个数");
        Scanner scanner = new Scanner(System.in);

        while (scanner.hasNextDouble()){

            double a = scanner.nextDouble();
            System.out.println("请输入操作符");
            String str = scanner.next();
            System.out.println("请输入第二个数");
            double b = scanner.nextDouble();
            switch (str){
                case "+":
                    add(a,b);
                    break;
                case "-":
                    minus(a,b);
                    break;
                case "*":
                    multiply(a,b);
                    break;
                case "/":
                    except(a,b);
                    break;
                default:
                    System.out.println("输入运算错误");
                    break;

            }



        }


        scanner.close();

    }

    public static void add(double num1,double num2) {
        System.out.println(num1 + num2);

    }
    public static void minus(double num1,double num2) {
        System.out.println(num1 - num2);

    }
    public static void multiply(double num1,double num2) {
        System.out.println(num1 * num2);

    }
    public static void except(double num1,double num2) {
        if (num2 == 0){
            System.out.println("分母不为0");
        }else {
            System.out.println(num1 / num2);
        }

    }

}