方法使用小练

方法的重载

public class Demo02 {
    public static void main(String[] args) {
        int max = max(10,10);
        System.out.println(max);
    }
    //方法的重载：方法可以重名，但是要参数类型不同
    public static double max(double num1,double num2){

        double result = 0;

        if(num1 == num2){
            System.out.println("num1==num2");
            return 0;
        }

        if(num1 > num2){
            result = num1;
        }else{
            result = num2;
        }

        return result;
    }
    //比大小
    public static int max(int num1,int num2){

        int result = 0;

        if(num1 == num2){
            System.out.println("num1==num2");
            return 0;//终止方法
        }

        if(num1 > num2){
            result = num1;
        }else{
            result = num2;
        }

        return result;
    }
}

可变参数的使用

public class Demo04 {
    public static void main(String[] args) {
        Demo04 demo04 = new Demo04();
        demo04.test(1,2,3,4,5);

    }

    //这样比比较麻烦，可以用可变参数
    public void method(){}
    public void method(int i){}
    public void method(int i,int i2){}
    public void method(int i,int i2,int i3){}
    //可变参数
    public void test(int... i){
        System.out.println(i[0]);
        System.out.println(i[1]);
    }
}

输出几个数的最大值

public class maxDemo {
    //输出几个数中的最大值
    public static void main(String[] args) {
        printMax(1,2,5,41,35.5);
        printMax(new double[]{1,2,5,64,84});//此处不能写为new double[1,2,3,4,5],会报错
    }
    public static void printMax(double...x){
        if(x.length == 0){
            System.out.println("没有输入数据");
            return ;
        }
        double result =x[0];
        for(int i = 1;i<x.length;i++){//将大的值赋值给result用来返回
            if(x[i]>result){
                result = x[i];
            }
        }
        System.out.println("最大值为：" + result);

    }
}

递归计算阶乘

• 尽量避免使用递归

public class Demo06 {
    //计算阶乘
    public static void main(String[] args) {
        System.out.println(f(5));
    }

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

一个有问题的计算程序

• scanner.close()后，运行到scanner.nextDouble处时出现异常NoSuchElementException
• 解决办法是删除scanner.close（）语句，或者不循环

import java.util.Scanner;

public class calculatorTest {
    public static void main(String[] args) {

        while(true) {
            Scanner scanner = new Scanner(System.in);

            System.out.println("请输入第一个数");
            double a1 = scanner.nextDouble();

            System.out.println("请输入第二个数");
            double a2 = scanner.nextDouble();

            System.out.println("请输入运算符");

            String str = scanner.next();//此处用scanner.nextLine()会直接赋值为空并进入switch

                switch (str) {
                    case "+":
                        System.out.println(add(a1, a2));
                        break;
                    case "-":
                        System.out.println(subtraction(a1, a2));
                        break;
                    case "*":
                        System.out.println(multiplication(a1, a2));
                        break;
                    case "/":
                        System.out.println(division(a1, a2));
                        break;
                    default:
                        System.out.println("符号输入错误，请重新输入");
                }
            scanner.close();
        }

    }
    public static double add(double x,double y){//定义加法
        return x+y;
    }
    public static double subtraction(double x,double y){//定义减法
        return x-y;
    }
    public static double multiplication(double x,double y){//定义乘法
        return x*y;
    }
    public static double division(double x,double y){//定义除法
        return x/y;
    }
}