方法

package function;

public class Demo1 {
    public static void main(String[] args) {
        int a = add(1,2);
        System.out.println(a);
        System.out.println(add(1,2,3,1.0));
        System.out.println(add(1.0,5.2));
    }
    public static int add(int a,int b){
        int sum = 0;
        sum = a + b;
        return sum;
    }

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

    public static int add(int a,int b,int c){
        return add(a,b) + c;
    }
    public static double add(int a,int b,int c,double d){
        double sum = add(a,b,c);
        return sum+d;
    }
}

命令行传参

package function;

public class Demo2 {
    public static void main(String[] args) {
        for (int i = 0; i < args.length; i++) {
            System.out.println("args[" + i + "]" + args[i]);
        }
    }
}

可以通过命令行进行参数传递，javac 类名 编译

然后因为类里面有包名，所以进行回退，回退至包名的上一级文件夹中进行java执行语句java function.Demo2 【传递的参数String类型】

可变参数

package function;

public class Demo3 {
    public static void main(String[] args) {
        method("this a test","fssd","fdfsdfsd");//传入的那一串参数必须是相同的类型
    }

    public static void method(String ...a){//可变长参数必须在最后面，
        for (int i = 0; i < a.length; i++) {
            System.out.println(a[i]);
        }
    }
}

递归

package function;
//递归实现阶层
public class Demo5 {
  public static void main(String[] args) {
      Demo5 demo5 = new Demo5();
      long test = demo5.test(2);
      System.out.println(test);
  }
  public long test(long n){
      if (n == 1) {
          return 1;
      }else {
          return test(n-1)*n;
      }

  }
}

package function;

import java.util.Scanner;
//实现计算器交互
public class Demo4 {
    public static void main(String[] args) {
        Demo4 demo4 = new Demo4();
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入运算数：");
        while (scanner.hasNextDouble()){
            double a = scanner.nextDouble();
            String s = scanner.next();
            double b = scanner.nextDouble();
            switch (s){
                case "+" :
                    System.out.println(demo4.add(a,b));;
                    break;
                case "-" :
                    System.out.println(demo4.minus(a,b));
                    break;
                case "*" :
                    System.out.println(demo4.multiply(a,b));
                    break;
                case "/" :
                    System.out.println(demo4.except(a,b));
                    break;
                default:
                    System.out.println("请输入合适字符");
            }
            System.out.println("请输入任意字符退出！");
        }

        scanner.close();
    }
    public double add(double a,double b){
        return a+b;
    }
    public double minus(double a,double b){
        return a-b;
    }
    public double multiply(double a,double b){
        return a*b;
    }
    public double except(double a,double b){
        return a/b;
    }
}